+---------------+-------------------------------+-------------+
| | | Probable |
| Groups. | Formations. | European |
| | | Equivalent. |
+---------------+-------------------------------+-------------+
/ | Chautauquan. | Chemung beds with Catskill | Famennien. |
U | | | as a local facies. | |
P | | | | |
P < | ( | Portage beds (Naples, Ithaca | Frasnien. |
E | | ( | and Oneonta shales as local | |
R | | Senecan. < | facies). | |
. | | ( | Genesee shales. | |
\ | ( | Tully limestone. | |
+---------------+-------------------------------+-------------+
M / | Erian. ( | Hamilton shale. | Givétien. |
I | | ( | Marcellus shale. | |
D | | | | |
D < | ( | Onondaga (Corniferous) | Eifélien. |
L | | Ulsterian. ( | limestone. | |
E | | < | Schoharie grit. | |
. \ | ( | Esopus grit (Caudagalli grit).| |
+---------------+-------------------------------+-------------+
L / | Oriskanian. | Oriskany sandstone. | Coblentzien.|
O | | | | |
W | | ( | Kingston beds. | Gédinnien. |
E < |Helderbe- ( | Becraft limestone. | |
R | | rgian. < | New Scotland beds. | |
. | | ( | Coeymans limestone. | |
\ +---------------+-------------------------------+-------------+
Although the correlation of the strata has only advanced a short
distance, there is no doubt as to the presence of undifferentiated
Devonian rocks in many parts of the continent. In the Great Plains
this system appears to be absent, but it is represented in Colorado,
Utah, Nevada, Wyoming, Montana, California and Arizona; Devonian rocks
occur between the Sierras and the Rocky Mountains, in the Arbuckle
Mountains of Oklahoma and in Texas. In the western interior limestones
predominate; 6000 ft. of limestone are found at Eureka, Nevada,
beneath 2000 ft. of shale. On the Pacific coast metamorphism of the
rocks is common, and lava-flows and tuffs occur in them.
In Canada, besides the occurrences previously mentioned in the eastern
region, Devonian strata are found in considerable force along the
course of the Mackenzie river and the Canadian Rockies, whence they
stretch out into Alaska. It is probable, however, that much that is
now classed as Devonian in Canada will prove on fossil evidence to be
Carboniferous.
_South America, Africa, Australia, &c._--In South America the Devonian
is well developed; in Argentina, Bolivia, Brazil, Peru and the
Falkland Islands, the palaeontological horizon is about the junction
of the Lower and Middle divisions, and the fauna has affinities with
the Hamilton shales of North America. Nearly allied to the South
American Devonian is that of South Africa, where they are represented
by the Bokkeveld beds in the Cape system. In Australia we find Lower
Devonian consisting of coarse littoral deposits with volcanic rocks;
and a Middle division with coral limestones in Victoria, New South
Wales and Queensland; an Upper division has also been observed. In New
Zealand the Devonian is well exposed in the Reefton mining field; and
it has been suggested that much of the highly metamorphosed rock may
belong to this system.
_Stratigraphy of the Old Red Sandstone Facies._
The Old Red Sandstone of Britain, according to Sir Archibald Geikie,
"consists of two subdivisions, the lower of which passes down
conformably into the Upper Silurian deposits, the upper shading off
in the same manner into the base of the Carboniferous system, while
they are separated from each other by an unconformability." The Old
Red strata appear to have been deposited in a number of elongated
lakes or lagoons, approximately parallel to one another, with a
general alignment in a N.E.-S.W. direction. To these areas of deposit
Sir A. Geikie has assigned convenient distinctive names.
In Scotland the two divisions of the system are sharply separated by a
pronounced unconformability which is probably indicative of a
prolonged interval of erosion. In the central valley between the base
of the Highlands and the southern uplands lay "Lake Caledonia." Here
the lower division is made up of some 20,000 ft. of shallow-water
deposits, reddish-brown, yellow and grey sandstones and conglomerates,
with occasional "cornstones," and thin limestones. The grey flagstones
with shales are almost confined to Forfarshire, and are known as the
"Arbroath flags." Interbedded volcanic rocks, andesites, dacites,
diabases, with agglomerates and tuffs constitute an important feature,
and attain a thickness of 6000 ft. in the Pentland and Ochil hills. A
line of old volcanic vents may be traced in a direction roughly
parallel to the trend of the great central valley. On the northern
side of the Highlands was "Lake Orcadie," presumably much larger than
the foregoing lake, though its boundaries are not determinable. It lay
over Moray Firth and the east of Ross and Sutherland, and extended
from Caithness to the Orkney Islands and S. Shetlands. It may even
have stretched across to Norway, where similar rocks are found in
Sognefjord and Dalsfjord, and may have had communications with some
parts of northern Russia. Very characteristic of this area are the
Caithness flags, dark grey and bituminous, which, with the red
sandstones and conglomerates at their base, probably attain a
thickness of 16,000 ft. The somewhat peculiar fauna of this series led
Murchison to class the flags as Middle Devonian. In the Shetland
Islands contemporaneous volcanic rocks have been observed. Over the
west of Argyllshire lay "Lake Lorne"; here the volcanic rocks
predominate, they are intercalated with shallow-water deposits. A
similar set of rocks occupy the Cheviot district.
The upper division of the Old Red Sandstone is represented in
Shropshire and South Wales by a great series of red rocks, shales,
sandstones and marls, some 10,000 ft. thick. They contain few fossils,
and no break has yet been found in the series. In Scotland this series
was deposited in basins which correspond only partially with those of
the earlier period. They are well developed in central Scotland over
the lowlands bordering the Moray Firth. Interbedded lavas and tuffs
are found in the island of Hoy. An interesting feature of this series
is the occurrence of great crowds of fossil fishes in some localities,
notably at Dura Den in Fife. In the north of England this series rests
unconformably upon the Lower Old Red and the Silurian.
Flanking the Silurian high ground of Cumberland and Westmorland, and
also in the Lammermuir hills and in Flint and Anglesey, a brecciated
conglomerate, presenting many of the characters of a glacial deposit
in places, has often been classed with the Old Red Sandstone, but in
parts, at least, it is more likely to belong to the base of the
Carboniferous system. In Ireland the lower division appears to be
represented by the Dingle beds and Glengariff grits, while the Kerry
rocks and the Kiltorcan beds of Cork are the equivalents of the upper
division. Rocks of Old Red type, both lower and upper, are found in
Spitzbergen and in Bear Island. In New Brunswick and Nova Scotia the
Old Red facies is extensively developed. The Gaspé sandstones have
been estimated at 7036 ft. thick. In parts of western Russia Old Red
Sandstone fossils are found in beds intercalated with others
containing marine fauna of the Devonian facies.
_Devonian and Old Red Sandstone Faunas._
The two types of sediment formed during this period--the _marine_
Devonian and the _lagoonal_ Old Red Sandstone--representing as they do
two different but essentially contemporaneous phases of physical
condition, are occupied by two strikingly dissimilar faunas. Doubtless
at all times there were regions of the earth that were marked off no
less clearly from the normal marine conditions of which we have
records; but this period is the earliest in which these variations of
environment are made obvious. In some respects the faunal break
between the older Silurian below and the younger Carboniferous above
is not strongly marked; and in certain areas a very close relationship
can be shown to exist between the older Devonian and the former, and
the younger Devonian and the latter. Nevertheless, taken as a whole,
the life of this period bears a distinct stamp of individuality.
The two most prominent features of the Devonian seas are presented by
corals and brachiopods. The corals were abundant individually and
varied in form; and they are so distinctive of the period that no
Devonian species has yet been found either in the Silurian or in the
Carboniferous. They built reefs, as in the present day, and
contributed to the formation of limestone masses in Devonshire, on the
continent of Europe and in North America. Rugose and tabulate forms
prevailed; among the former the cyathophyllids (_Cyathophyllum_) were
important, _Phillipsastraea_, _Zaphrentis_, _Acervularia_ and the
curious _Calceola_ (_sandalina_), an operculate genus which has given
palaeontologists much trouble in its diagnosis, for it has been
regarded as a pelecypod (hippurite) and a brachiopod. The tabulate
corals were represented by _Favosites_, _Michelinia_, _Pleurodictyum_,
_Fistulipora_, _Pachypora_ and others. _Heliolites_ and _Plasmopora_
represent the alcyonarians. Stromatoporoids were important reef
builders. A well-known fossil is _Receptaculites_, a genus to which it
has been difficult to assign a definite place; it has been thought to
be a sponge, it may be a calcareous alga, or a curious representative
of the foraminifera.
In the Devonian period the brachiopods reached the climax of their
development: they compose three-quarters of the known fauna, and more
than 1100 species have been described. Changes were taking place from
the beginning of the period in the relative importance of genera;
several Silurian forms dropped out, and new types were coming in. A
noticeable feature was the development of broad-winged shells in the
genus _Spirifer_, other spiriferids were _Ambocoelia_, _Uncites_,
_Verneuilia_. Orthids and pentamerids were waning in importance, while
the productids (_Productella_, _Chonetes_, _Strophalosia_) were
increasing. The strophomenids were still flourishing, represented by
the genera _Leptaena_, _Stropheodonta_, _Kayserella_, and others. The
ancient _Lingula_, along with _Crania_ and _Orbiculoidea_, occur among
the inarticulate forms. Another long-lived and wide-ranging species is
_Atrypa reticularis_. The athyrids were very numerous (_Athyris_,
_Retzia_, _Merista_, _Meristella_, _Kayserina_, &c.); and the
rhynchonellids were well represented by _Pugnax_, _Hypothyris_, and
several other genera. The important group of terebratulids appears in
this system; amongst them _Stringocephalus_ is an eminently
characteristic Devonian brachiopod; others are _Dielasma_,
_Cryptonella_, _Rensselaeria_ and _Oriskania_.
The pelecypod molluscs were represented by _Pterinea_, abundant in the
lower members along with other large-winged forms, and by
_Cucullella_, _Buchiola_ and _Curtonotus_ in the upper members of the
system. Other genera are _Actinodesma_, _Cardiola_, _Nucula_,
_Megalodon_, _Aviculopecten_, &c. Gasteropods were becoming more
important, but the simple capulid forms prevailed: _Platyceras_
(_Capulus_), _Straparollus_, _Pleurotomaria_, _Murchisonia_,
_Macrocheilina_, _Euomphalus_. Among the pteropods, _Tentaculites_ was
very abundant in some quarters; others were _Conularia_ and
_Styliolina_. In the Devonian period the cephalopods began to make a
distinct advance in numbers, and in development. The goniatites appear
with the genera _Anarcestes_, _Agoniatites_, _Tornoceras_, _Bactrites_
and others; and in the upper strata the clymenoids, forerunners of the
later ammonoids, began to take definite shape. While several new
nautiloids (_Homaloceras_, _Ryticeras_, &c.) made their appearance
several of the older genera still lived on (_Orthoceras_,
_Poterioceras_, _Actinoceras_).
Crinoids were very abundant in some parts of the Devonian sea, though
they were relatively scarce in others; they include the genera
_Melocrinus_, _Haplocrinus_, _Cupressocrinus_, _Calceocrinus_ and
_Eleuthrocrinus_. The cystideans were falling off (_Proteocystis_,
_Tiaracrinus_), but blastoids were in the ascendant (_Nucleocrinus_,
_Codaster_, &c.). Both brittle-stars, _Ophiura_, _Palaeophiura_,
_Eugaster_, and true starfishes, _Palaeaster_, _Aspidosoma_, were
present, as well as urchins (_Lepidocentrus_).
When we turn to the crustaceans we have to deal with two distinct
assemblages, one purely marine, trilobitic, the other mainly
lacustrine or lagoonal with a eurypteridian facies. The trilobites had
already begun to decline in importance, and as happens not
infrequently with degenerating races of beasts and men, they began to
develop strange eccentricities of ornamentation in some of their
genera. A number of Silurian genera lived on into the Devonian period,
and some gradually developed into new and distinctive forms; such were
_Proëtus_, _Harpes_, _Cheirurus_, _Bronteus_ and others. Distinct
species of _Phacops_ mark the Lower and Upper Devonian respectively,
while the genus _Dalmania_ (_Odontochile_) was represented by species
with an almost world-wide range. The Ostracod _Entomis_ (_Cypridina_)
was extremely abundant in places--_Cypridinen-Schiefer_--while the
true _Cypridina_ was also present along with _Beyrichia_,
_Leperditia_, &c. The Phyllocarids, _Echinocaris_, _Eleuthrocaris_,
_Tropidocaris_, are common in the United States. It is in the Old Red
Sandstone that the eurypterids are best preserved; foremost among
these was _Pterygotus_; _P. anglicus_ has been found in Scotland with
a length of nearly 6 ft.; _Eurypterus_, _Slimonia_, _Stylonurus_ were
other genera.
Insects appear well developed, including both orthopterous and
neuropterous forms, in the New Brunswick rocks. Mr Scudder believed he
had obtained a specimen of Orthoptera in which a stridulating organ
was present. A species of _Ephemera_, allied to the modern may-fly,
had a spread of wing extending to 5 in. In the Scottish Old Red
Sandstone myriapods, _Kampecaris_ and _Archidesmus_, have been
described; they are somewhat simpler than more recent forms, each
segment being separate, and supplied with only one pair of walking
legs. Spiders and scorpions also lived upon the land.
The great number of fish remains in the Devonian and Old Red strata,
coupled with the truly remarkable characters possessed by some of the
forms, has caused the period to be described as the "age of fishes."
As in the case of the crustaceans, referred to above, we find one
assemblage more or less peculiar to the freshwater or brackish
conditions of the Old Red, and another characteristic of the marine
Devonian; on the whole the former is the richer in variety, but there
seems little doubt that quite a number of genera were capable of
living in either environment, whatever may have been the real
condition of the Old Red waters. Foremost in interest are the curious
ostracoderms, a remarkable group of creatures possessing many of the
characteristics of fishes, but more probably belonging to a distinct
class of organisms, which appears to link the vertebrates with the
arthropods. They had come into existence late in Silurian times; but
it is in the Old Red strata that their remains are most fully
preserved. They were abundant in the fresh or brackish waters of
Scotland, England, Wales, Russia and Canada, and are represented by
such forms as _Pteraspis_, _Cephalaspis_, _Cyathaspis_, _Tremataspis_,
_Bothriolepis_ and _Pterichthys_.
In the lower members of the Old Red series _Dipterus_, and in the
upper members _Phaneropleuron_, represented the dipnoid lung-fishes;
and it is of extreme interest to note that a few of these curious
forms still survive in the African _Protopterus_, the Australian
_Ceratodus_ and the South American _Lepidosiren_,--all freshwater
fishes. Distantly related to the lung-fishes were the singular
arthrodirans, a group possessing the unusual faculty of moving the
head in a vertical plane. These comprise the wide-ranging _Coccosteus_
with _Homosteus_ and _Dinichthys_, the largest fish of the period. The
latter probably reached 20 ft. in length; it was armed with
exceedingly powerful jaws provided with turtle-like beaks. Sharks were
fairly prominent denizens of the sea; some were armed with cutting
teeth, others with crushing dental plates; and although they were on
the whole marine fishes, they were evidently able to live in fresher
waters, like some of their modern representatives, for their remains,
mostly teeth and large dermal spines, are found both in the Devonian
and Old Red rocks. _Mesacanthus_, _Diplacanthus_, _Climatius_,
_Cheiracanthus_ are characteristic genera. The crossopterygians,
ganoids with a scaly lobe in the centre of the fins, were represented
by _Holoptychius_ and _Glyptopomus_ in the Upper Old Red, and by such
genera as _Diplopterus_, _Osteolepis_, _Gyroptychius_ in the lower
division. The _Polypterus_ of the Nile and _Calamoichthys_ of South
Africa are the modern exemplars of this group. _Cheirolepis_, found in
the Old Red of Scotland and Canada, is the only Devonian
representative of the actinopterygian fishes. The cyclostome fishes
have, so far, been discovered only in Scotland, in the tiny
_Palaeospondylus_. Amphibian remains have been found in the Devonian
of Belgium; and footprints supposed to belong to a creature of the
same class (_Thinopus antiquus_) have been described by Professor
Marsh from the Chemung formation of Pennsylvania.
_Plant Life._--In the lacustrine deposits of the Old Red Sandstone we
find the earliest well-defined assemblage of terrestrial plants. In
some regions so abundant are the vegetable remains that in places they
form thin seams of veritable coal. These plants evidently flourished
around the shores of the lakes and lagoons in which their remains were
buried along with the other forms of life. Lycopods and ferns were the
predominant types; and it is important to notice that both groups were
already highly developed. The ferns include the genera _Sphenopteris_,
_Megalopteris_, _Archaeopteris_, _Neuropteris_. Among the Lycopods are
_Lycopodites_, _Psilophyton_, _Lepidodendron_. Modern horsetails are
represented by _Calamocladus_, _Asterocalamites_, _Annularia_. Of
great interest are the genera _Cordaites_, _Araucarioxylon_, &c.,
which were synthetic types, uniting in some degree the Coniferae and
the Cycadofilicales. With the exception of obscure markings, aquatic
plants are not so well represented as might have been expected;
_Parka_, a common fossil, has been regarded as a water plant with a
creeping stem and two kinds of sporangia in sessile sporocarps.
_Physical Conditions, &c._--Perhaps the most striking fact that is
brought out by a study of the Devonian rocks and their fossils is the
gradual transgression of the sea over the land, which took place quietly
in every quarter of the globe shortly after the beginning of the period.
While in most places the Lower Devonian sediments succeed the Silurian
formations in a perfectly conformable manner, the Middle and Upper
divisions, on account of this encroachment of the sea, rest
unconformably upon the older rocks, the Lower division being
unrepresented. This is true over the greater part of South America, so
far as our limited knowledge goes, in much of the western side of North
America, in western Russia, in Thuringia and other parts of central
Europe. Of the distribution of land and sea and the position of the
coast lines in Devonian times we can state nothing with precision. The
known deposits all point to shallow waters of epicontinental seas; no
abyssal formations have been recognized. E. Kayser has pointed out the
probability of a Eurasian sea province extending through Europe towards
the east, across north and central Asia towards Manitoba in Canada, and
an American sea province embracing the United States, South America and
South Africa. At the same time there existed a great North Atlantic land
area caused partly by the uplift of the Caledonian range just before the
beginning of the period, which stretched across north Europe to eastern
Canada; on the fringe of this land the Old Red Sandstone was formed.
In the European area C. Barrois has indicated the existence of three
zones of deposition: (1) A northern, Old Red, region, including Great
Britain, Scandinavia, European Russia and Spitzbergen; here the land was
close at hand; great brackish lagoons prevailed, which communicated more
or less directly with the open sea. In European Russia, during its
general advance, the sea occasionally gained access to wide areas, only
to be driven off again, during pauses in the relative subsidence of the
land, when the continued terrigenous sedimentation once more established
the lagoonal conditions. These alternating phases were frequently
repeated. (2) A middle region, covering Devonshire and Cornwall, the
Ardennes, the northern part of the lower Rhenish mountains, and the
upper Harz to the Polish Mittelgebirge; here we find evidence of a
shallow sea, clastic deposits and a sublittoral fauna. (3) A southern
region reaching from Brittany to the south of the Rhenish mountains,
lower Harz, Thuringia and Bohemia; here was a deeper sea with a more
pelagic fauna. It must be borne in mind that the above-mentioned regions
are intended to refer to the time when the extension of the Devonian sea
was near its maximum. In the case of North America it has been shown
that in early and middle Devonian time more or less distinct faunas
invaded the continent from five different centres, viz. the Helderberg,
the Oriskany, the Onondaga, the southern Hamilton and the north-western
Hamilton; these reached the interior approximately in the order given.
Towards the close of the period, when the various local faunas had
mingled one with another and a more generalized life assemblage had been
evolved, we find many forms with a very wide range, indicating great
uniformity of conditions. Thus we find identical species of brachiopods
inhabiting the Devonian seas of England, France, Belgium, Germany,
Russia, southern Asia and China; such are, _Hypothyris_ (_Rhynchonella_)
_cuboides_, _Spirifer disjunctus_ and others. The fauna of the
_Calceola_ shales can be traced from western Europe to Armenia and
Siberia; the _Stringocephalus_ limestones are represented in Belgium,
England, the Urals and Canada; and the (_Gephyroceras_) _intumescens_
shales are found in western Europe and in Manitoba.
The Devonian period was one of comparative quietude; no violent crustal
movements seem to have taken place, and while some changes of level
occurred towards its close in Great Britain, Bohemia and Russia,
generally the passage from Devonian to Carboniferous conditions was
quite gradual. In later periods these rocks have suffered considerable
movement and metamorphism, as in the Harz, Devonshire and Cornwall, and
in the Belgian coalfields, where they have frequently been thrust over
the younger Carboniferous rocks. Volcanic activity was fairly
widespread, particularly during the middle portion of the period. In the
Old Red rocks of Scotland there is a great thickness (6000 ft.) of
igneous rocks, including diabases and andesitic lavas with agglomerates
and tuffs. In Devonshire diabases and tuffs are found in the middle
division. In west central Europe volcanic rocks are found at many
horizons, the most common rocks are diabases and diabase tuffs,
_schalstein_. Felsitic lavas and tuffs occur in the Middle Devonian of
Australia. Contemporaneous igneous rocks are generally absent in the
American Devonian, but in Nova Scotia and New Brunswick there appear to
be some.
There is little evidence as to the climate of this period, but it is
interesting to observe that local glacial conditions _may_ have existed
in places, as is suggested by the coarse conglomerate with striated
boulders in the upper Old Red of Scotland. On the other hand, the
prevalence of reef-building corals points to moderately warm
temperatures in the Middle Devonian seas.
The economic products of Devonian rocks are of some importance: in many
of the metamorphosed regions veins of tin, lead, copper, iron are
exploited, as in Cornwall, Devon, the Harz; in New Zealand, gold veins
occur. Anthracite of Devonian age is found in China and a little coal in
Germany, while the Upper Devonian is the chief source of oil and gas of
western Pennsylvania and south-western New York. In Ontario the middle
division is oil-bearing. Black phosphates are worked in central
Tennessee, and in England the marls of the "Old Red" are employed for
brick-making.
REFERENCES.--The literature of the Devonian rocks and fossils is very
extensive; important papers have been contributed by the following
geologists: J. Barrande, C. Barrois, F. Béclard, E. W. Benecke, L.
Beushausen, A. Champernowne, J. M. Clarke, Sir J. W. Dawson, A.
Denckmann, J. S. Diller, E. Dupont, F. Frech, J. Fournet, Sir A.
Geikie, G. Gürich, R. Hoernes, E. Kayser, C. and M. Koch, A. von
Koenen, Hugh Miller, D. P. Oehlert, C. S. Prosser, P. de Rouville, C.
Schuchert, T. Tschernyschew, E. O. Ulrich, W. A. E. Ussher, P. N.
Wenjukoff, G. F. Whidborne, J. F. Whiteaves and H. S. Williams.
Sedgwick and Murchison's original description appeared in the _Trans.
Geol. Soc._ (2nd series, vol. v., 1839). Good general accounts will be
found in Sir A. Geikie's _Text-Book of Geology_ (vol. ii., 4th ed.,
1903), in E. Kayser's _Lehrbuch der Geologie_ (vol. ii., 2nd ed.,
1902), and, for North America, in Chamberlin and Salisbury's _Geology_
(vol. ii., 1906). See the _Index to the Geological Magazine_
(1864-1903), and in subsequent annual volumes; _Geological Literature
added to the Geological Society's Library_ (London), annually since
1893; and the _Neues Jahrbuch für Min., Geologie und Paläontologie_
(Stuttgart, 2 annual volumes). The U.S. Geological Survey publishes at
intervals a _Bibliography and Index of North American Geology, &c._,
and this (e.g. Bulletin 301,--the _Bibliog. and Index_ for 1901-1905)
contains numerous references for the Devonian system in North America.
(J. A. H.)
DEVONPORT, a municipal, county and parliamentary borough of Devonshire,
England, contiguous to East Stonehouse and Plymouth, the seat of one of
the royal dockyards, and an important naval and military station. Pop.
(1901) 70,437. It is situated immediately above the N.W. angle of
Plymouth Sound, occupying a triangular peninsula formed by Stonehouse
Pool on the E. and the Hamoaze on the W. It is served by the Great
Western and the London & South Western railways. The town proper was
formerly enclosed by a line of ramparts and a ditch excavated out of the
limestone, but these are in great part demolished. Adjoining Devonport
are East Stonehouse (an urban district, pop. 15,111), Stoke and Morice
Town, the two last being suburbs of Devonport. The town hall, erected in
1821-1822 partly after the design of the Parthenon, is distinguished by
a Doric portico; while near it are the public library, in Egyptian
style, and a conspicuous Doric column built of Devonshire granite. This
monument, which is 100 ft. high, was raised in commemoration of the
naming of the town in 1824. Other institutions are the Naval Engineering
College, Keyham (1880); the municipal technical schools, opened in 1899,
the majority of the students being connected with the dockyard; the
naval barracks, Keyham (1885); the Raglan barracks and the naval and
military hospitals. On Mount Wise, which was formerly defended by a
battery (now a naval signalling station), stands the military residence,
or Government House, occupied by the commander of the Plymouth Coast
Defences; and near at hand is the principal naval residence, the naval
commander-in-chief's house. The prospect from Mount Wise over the
Hamoaze to Mount Edgecumbe on the opposite shore is one of the finest in
the south of England. The most noteworthy feature of Devonport, however,
is the royal dockyard, originally established by William III. in 1689
and until 1824 known as Plymouth Dock. It is situated within the old
town boundary and contains four docks. To this in 1853 was added Keyham
steamyard, situated higher up the Hamoaze beyond the old boundary and
connected with the Devonport yard by a tunnel. In 1896 further
extensions were begun at the Keyham yard, which became known as
Devonport North yard. Before these were begun the yard comprised two
basins, the northern one being 9 acres and the southern 7 acres in area,
and three docks, having floor-lengths of 295, 347 and 413 ft., together
with iron and brass foundries, machinery shops, engineer students' shop,
&c. The new extensions, opened by the Prince of Wales on the 21st of
February 1907, cover a total area of 118 acres lying to the northward in
front of the Naval Barracks, and involved the reclamation of 77 acres of
mudflats lying below high-water mark. The scheme presented three leading
features--a tidal basin, a group of three graving docks with entrance
lock, and a large enclosed basin with a coaling depôt at the north end.
The tidal basin, close to the old Keyham north basin, is 740 ft. long
with a mean width of 590 ft., and has an area of 10 acres, the depth
being 32 ft. at low water of spring tides. It affords access to two
graving docks, one with a floor-length of 745 ft. and 20½ ft. of water
over the sill, and the other with a length of 741 ft. and 32 ft. of
water over the sill. Each of these can be subdivided by means of an
intermediate caisson, and (when unoccupied) may serve as an entrance to
the closed basin. The lock which leads from the tidal to the closed
basin is 730 ft. long, and if necessary can be used as a dock. The
closed basin, out of which opens a third graving dock, 660 ft. long,
measures 1550 ft. by 1000 ft. and has an area of 35½ acres, with a depth
of 32 ft. at low-water springs; it has a direct entrance from the
Hamoaze, closed by a caisson. The foundations of the walls are carried
down to the rock, which in some places lies covered with mud 100 ft. or
more below coping level. Compressed air is used to work the sliding
caissons which close the entrances of the docks and closed basin. A
ropery at Devonport produces half the hempen ropes used in the navy.
By the Reform Act of 1832 Devonport was erected into a parliamentary
borough including East Stonehouse and returning two members. The ground
on which it stands is for the most part the property of the St Aubyn
family (Barons St Levan), whose steward holds a court leet and a court
baron annually. The town is governed by a mayor, sixteen aldermen and
forty-eight councillors. Area, 3044 acres.
DEVONPORT, EAST and WEST, a town of Devon county, Tasmania, situated on
both sides of the mouth of the river Mersey, 193 m. by rail N.W. of
Hobart. Pop. (1901), East Devonport, 673, West Devonport, 2101. There is
regular communication from this port to Melbourne and Sydney, and it
ranks as the third port in Tasmania. A celebrated regatta is held on the
Mersey annually on New Year's day.
DEVONSHIRE, EARLS AND DUKES OF. The Devonshire title, now in the
Cavendish family, had previously been held by Charles Blount
(1563-1606), 8th Lord Mountjoy, great-grandson of the 4th Lord Mountjoy
(d. 1534), the pupil of Erasmus; he was created earl of Devonshire in
1603 for his services in Ireland, where he became famous in subduing the
rebellion between 1600 and 1603; but the title became extinct at his
death. In the Cavendish line the 1st earl of Devonshire was William (d.
1626), second son of Sir William Cavendish (q.v.), and of Elizabeth
Hardwick, who afterwards married the 6th earl of Shrewsbury. He was
created earl of Devonshire in 1618 by James I., and was succeeded by
William, 2nd earl (1591-1628), and the latter by his son William
(1617-1684), a prominent royalist, and one of the original members of
the Royal Society, who married a daughter of the 2nd earl of Salisbury.
WILLIAM CAVENDISH, 1st duke of Devonshire (1640-1707), English
statesman, eldest son of the earl of Devonshire last mentioned, was born
on the 25th of January 1640. After completing his education he made the
tour of Europe according to the custom of young men of his rank, being
accompanied on his travels by Dr Killigrew. On his return he obtained,
in 1661, a seat in parliament for Derbyshire, and soon became
conspicuous as one of the most determined and daring opponents of the
general policy of the court. In 1678 he was one of the committee
appointed to draw up articles of impeachment against the lord treasurer
Danby. In 1679 he was re-elected for Derby, and made a privy councillor
by Charles II.; but he soon withdrew from the board with his friend Lord
Russell, when he found that the Roman Catholic interest uniformly
prevailed. He carried up to the House of Lords the articles of
impeachment against Lord Chief-Justice Scroggs, for his arbitrary and
illegal proceedings in the court of King's bench; and when the king
declared his resolution not to sign the bill for excluding the duke of
York, afterwards James II., he moved in the House of Commons that a bill
might be brought in for the association of all his majesty's Protestant
subjects. He also openly denounced the king's counsellors, and voted for
an address to remove them. He appeared in defence of Lord Russell at his
trial, at a time when it was scarcely more criminal to be an accomplice
than a witness. After the condemnation he gave the utmost possible proof
of his attachment by offering to exchange clothes with Lord Russell in
the prison, remain in his place, and so allow him to effect his escape.
In November 1684 he succeeded to the earldom on the death of his father.
He opposed arbitrary government under James II. with the same
consistency and high spirit as during the previous reign. He was
withdrawn from public life for a time, however, in consequence of a
hasty and imprudent act of which his enemies knew how to avail
themselves. Fancying that he had received an insulting look in the
presence chamber from Colonel Colepepper, a swaggerer whose attendance
at court the king encouraged, he immediately avenged the affront by
challenging the colonel, and, on the challenge being refused, striking
him with his cane. This offence was punished by a fine of £30,000, which
was an enormous sum even to one of the earl's princely fortune. Not
being able to pay he was imprisoned in the king's bench, from which he
was released only on signing a bond for the whole amount. This was
afterwards cancelled by King William. After his discharge the earl went
for a time to Chatsworth, where he occupied himself with the erection of
a new mansion, designed by William Talman, with decorations by Verrio,
Thornhill and Grinling Gibbons. The Revolution again brought him into
prominence. He was one of the seven who signed the original paper
inviting the prince of Orange from Holland, and was the first nobleman
who appeared in arms to receive him at his landing. He received the
order of the Garter on the occasion of the coronation, and was made lord
high steward of the new court. In 1690 he accompanied King William on
his visit to Holland. He was created marquis of Hartington and duke of
Devonshire in 1694 by William and Mary, on the same day on which the
head of the house of Russell was created duke of Bedford. Thus, to quote
Macaulay, "the two great houses of Russell and Cavendish, which had long
been closely connected by friendship and by marriage, by common
opinions, common sufferings and common triumphs, received on the same
day the highest honour which it is in the power of the crown to confer."
His last public service was assisting to conclude the union with
Scotland, for negotiating which he and his eldest son, the marquis of
Hartington, had been appointed among the commissioners by Queen Anne. He
died on the 18th of August 1707, and ordered the following inscription
to be put on his monument:-
Willielmus Dux Devon,
Bonorum Principum Fidelis Subditus,
Inimicus et Invisus Tyrannis.
He had married in 1661 the daughter of James, duke of Ormonde, and he
was succeeded by his eldest son William as 2nd duke, and by the latter's
son William as 3rd duke (viceroy of Ireland, 1737-1744). The latter's
son William (1720-1764) succeeded in 1755 as 4th duke; he married the
daughter and heiress of Richard Boyle, earl of Burlington and Cork, who
brought Lismore Castle and the Irish estates into the family; and from
November 1756 to May 1757 he was prime minister, mainly in order that
Pitt, who would not then serve under the duke of Newcastle, should be in
power. His son William (1748-1811), 5th duke, is memorable as the
husband of the beautiful Georgiana Spencer, duchess of Devonshire
(1757-1806), and of the intellectual Elizabeth Foster, duchess of
Devonshire (1758-1824), both of whom Gainsborough painted. His son
William, 6th duke (1790-1858), who died unmarried, was sent on a special
mission to the coronation of the tsar Nicholas at Moscow in 1826, and
became famous for his expenditure on that occasion; and it was he who
employed Sir Joseph Paxton at Chatsworth. The title passed in 1858 to
his cousin William (1808-1891), 2nd earl of Burlington, as 7th duke, a
man who, without playing a prominent part in public affairs, exercised
great influence, not only by his position but by his distinguished
abilities. At Cambridge in 1829 he was second wrangler, first Smith's
prizeman, and eighth classic, and subsequently he became chancellor of
the university.
SPENCER COMPTON CAVENDISH, 8th duke (1833-1908), born on the 23rd of
July 1833, was the son of the 7th duke (then earl of Burlington) and his
wife Lady Blanche Howard (sister of the earl of Carlisle). In 1854 Lord
Cavendish, as he then was, took his degree at Trinity College,
Cambridge; in 1856 he was attached to the special mission to Russia for
the new tsar's accession; and in 1857 he was returned to parliament as
Liberal member for North Lancashire. At the opening of the new
parliament of 1859 the marquis of Hartington (as he had now become)
moved the amendment to the address which overthrew the government of
Lord Derby. In 1863 he became first a lord of the admiralty, and then
under-secretary for war, and on the formation of the Russell-Gladstone
administration at the death of Lord Palmerston he entered it as war
secretary. He retired with his colleagues in July 1866; but upon Mr
Gladstone's return to power in 1868 he became postmaster-general, an
office which he exchanged in 1871 for that of secretary for Ireland.
When Mr Gladstone, after his defeat and resignation in 1874, temporarily
withdrew from the leadership of the Liberal party in January 1875, Lord
Hartington was chosen Liberal leader in the House of Commons, Lord
Granville being leader in the Lords. Mr W. E. Forster, who had taken a
much more prominent part in public life, was the only other possible
nominee, but he declined to stand. Lord Hartington's rank no doubt told
in his favour, and Mr Forster's education bill had offended the
Nonconformist members, who would probably have withheld their support.
Lord Hartington's prudent management in difficult circumstances laid his
followers under great obligations, since not only was the opposite party
in the ascendant, but his own former chief was indulging in the freedom
of independence. After the complete defeat of the Conservatives in the
general election of 1880, a large proportion of the party would have
rejoiced if Lord Hartington could have taken the Premiership instead of
Mr Gladstone, and the queen, in strict conformity with constitutional
usage (though Gladstone himself thought Lord Granville should have had
the preference), sent for him as leader of the Opposition. Mr Gladstone,
however, was clearly master of the situation: no cabinet could be formed
without him, nor could he reasonably be expected to accept a subordinate
post. Lord Hartington, therefore, gracefully abdicated the leadership,
and became secretary of state for India, from which office, in December
1882, he passed to the war office. His administration was memorable for
the expeditions of General Gordon and Lord Wolseley to Khartum, and a
considerable number of the Conservative party long held him chiefly
responsible for the "betrayal of Gordon." His lethargic manner, apart
from his position as war minister, helped to associate him in their
minds with a disaster which emphasized the fact that the government
acted "too late"; but Gladstone and Lord Granville were no less
responsible than he. In June 1885 he resigned along with his colleagues,
and in December was elected for the Rossendale Division of Lancashire,
created by the new reform bill. Immediately afterwards the great
political opportunity of Lord Hartington's life came to him in Mr
Gladstone's conversion to home rule for Ireland. Lord Hartington's
refusal to follow his leader in this course inevitably made him the
chief of the new Liberal Unionist party, composed of a large and
influential section of the old Liberals. In this capacity he moved the
first resolution at the famous public meeting at the opera house, and
also, in the House of Commons, moved the rejection of Mr Gladstone's
Bill on the second reading. During the memorable electoral contest which
followed, no election excited more interest than Lord Hartington's for
the Rossendale division, where he was returned by a majority of nearly
1500 votes. In the new parliament he held a position much resembling
that which Sir Robert Peel had occupied after his fall from power, the
leader of a small, compact party, the standing and ability of whose
members were out of all proportion to their numbers, generally esteemed
and trusted beyond any other man in the country, yet in his own opinion
forbidden to think of office. Lord Salisbury's offers to serve under him
as prime minister (both after the general election, and again when Lord
Randolph Churchill resigned) were declined, and Lord Hartington
continued to discharge the delicate duties of the leader of a middle
party with no less judgment than he had shown when leading the Liberals
during the interregnum of 1875-1880. It was not until 1895, when the
differences between Conservatives and Liberal Unionists had become
almost obliterated by changed circumstances, and the habit of acting
together, that the duke of Devonshire, as he had become by the death of
his father in 1891, consented to enter Lord Salisbury's third ministry
as president of the council. The duke thus was the nominal
representative of education in the cabinet at a time when educational
questions were rapidly becoming of great importance; and his own
technical knowledge of this difficult and intricate question being
admittedly superficial, a good deal of criticism from time to time
resulted. He had however by this time an established position in public
life, and a reputation for weight of character, which procured for him
universal respect and confidence, and exempted him from bitter attack,
even from his most determined political opponents. Wealth and rank
combined with character to place him in a measure above party; and his
succession to his father as chancellor of the university of Cambridge in
1892 indicated his eminence in the life of the country. In the same year
he had married the widow of the 7th duke of Manchester.
He continued to hold the office of lord president of the council till
the 3rd of October 1903, when he resigned on account of differences with
Mr BALFOUR (q.v.) over the latter's attitude towards free trade. As Mr
Chamberlain had retired from the cabinet, and the duke had not thought
it necessary to join Lord George Hamilton and Mr Ritchie in resigning a
fortnight earlier, the defection was unanticipated and was sharply
criticized by Mr Balfour, who, in the rearrangement of his ministry, had
only just appointed the duke's nephew and heir, Mr Victor Cavendish, to
be secretary to the treasury. But the duke had come to the conclusion
that while he himself was substantially a free-trader,[1] Mr Balfour did
not mean the same thing by the term. He necessarily became the leader of
the Free Trade Unionists who were neither Balfourites nor
Chamberlainites, and his weight was thrown into the scale against any
association of Unionism with the constructive policy of tariff reform,
which he identified with sheer Protection. A struggle at once began
within the Liberal Unionist organization between those who followed the
duke and those who followed Mr CHAMBERLAIN (q.v.); but the latter were
in the majority and a reorganization in the Liberal Unionist Association
took place, the Unionist free-traders seceding and becoming a separate
body. The duke then became president of the new organizations, the
Unionist Free Food League and the Unionist Free Trade Club. In the
subsequent developments the duke played a dignified but somewhat silent
part, and the Unionist rout in 1906 was not unaffected by his open
hostility to any taint of compromise with the tariff reform movement.
But in the autumn of 1907 his health gave way, and grave symptoms of
cardiac weakness necessitated his abstaining from public effort and
spending the winter abroad. He died, rather suddenly, at Cannes on the
24th of March 1908.
The head of an old and powerful family, a wealthy territorial magnate,
and an Englishman with thoroughly national tastes for sport, his weighty
and disinterested character made him a statesman of the first rank in
his time, in spite of the absence of showy or brilliant qualities. He
had no self-seeking ambitions, and on three occasions preferred not to
become prime minister. Though his speeches were direct and forcible, he
was not an orator, nor "clever"; and he lacked all subtlety of
intellect; but he was conspicuous for solidity of mind and
straightforwardness of action, and for conscientious application as an
administrator, whether in his public or private life. The fact that he
once yawned in the middle of a speech of his own was commonly quoted as
characteristic; but he combined a great fund of common sense and
knowledge of the average opinion with a patriotic sense of duty towards
the state. Throughout his career he remained an old-fashioned Liberal,
or rather Whig, of a type which in his later years was becoming
gradually more and more rare.
There was no issue of his marriage, and he was succeeded as 9th duke by
his nephew VICTOR CHRISTIAN CAVENDISH (b. 1868), who had been Liberal
Unionist member for West Derbyshire since 1891, and was treasurer of the
household (1900 to 1903) and financial secretary to the treasury (1903
to 1905); in 1892 he married a daughter of the marquess of Lansdowne, by
whom he had two sons. (H. CH.)
[1] His own words to Mr Balfour at the time were: "I believe that
our present system of free imports is on the whole the most advantageous
to the country, though I do not contend that the principles on
which it rests possess any such authority or sanctity as to forbid any
departure from it, for sufficient reasons."
DEVONSHIRE (DEVON), a south-western county of England, bounded N.W. and
N. by the Bristol Channel, N.E. by Somerset and Dorset, S.E. and S. by
the English Channel, and W. by Cornwall. The area, 2604.9 sq. m., is
exceeded only by those of Yorkshire and Lincolnshire among the English
counties. Nearly the whole of the surface is uneven and hilly. The
county contains the highest land in England south of Derbyshire
(excepting points on the south Welsh border); and the scenery, much
varied, is in most parts striking and picturesque. The heather-clad
uplands of Exmoor, though chiefly within the borders of Somerset, extend
into North Devon, and are still the haunt of red deer, and of the small
hardy ponies called after the district. Here, as on Dartmoor, the
streams are rich in trout. Dartmoor, the principal physical feature of
the county, is a broad and lofty expanse of moorland which rises in the
southern part. Its highest point, 2039 ft., is found in the
north-western portion. Its rough wastes contrast finely with the wild
but wooded region which immediately surrounds the granite of which it is
composed, and with the rich cultivated country lying beyond. Especially
noteworthy in this fertile tract are the South Hams, a fruitful district
of apple orchards, lying between the Erme and the Dart; the rich
meadow-land around Crediton, in the vale of Exeter; and the red rocks
near Sidmouth. Two features which lend a characteristic charm to the
Devonshire landscape are the number of picturesque old cottages roofed
with thatch; and the deep lanes, sunk below the common level of the
ground, bordered by tall hedges, and overshadowed by an arch of boughs.
The north and south coasts of the county differ much in character, but
both have grand cliff and rock scenery, not surpassed by any in England
or Wales, resembling the Mediterranean seaboard in its range of colour.
As a rule the long combes or glens down which the rivers flow seaward
are densely wooded, and the country immediately inland is of great
beauty. Apart from the Tamar, which constitutes the boundary between
Devon and Cornwall, and flows into the English Channel, after forming in
its estuary the harbours of Devonport and Plymouth, the principal rivers
rise on Dartmoor. These include the Teign, Dart, Plym and Tavy, falling
into the English Channel, and the Taw flowing north towards Bideford
Bay. The river Torridge, also discharging northward, receives part of
its waters from Dartmoor through the Okement, but itself rises in the
angle of high land near Hartland point on the north coast, and makes a
wide sweep southward. The lesser Dartmoor streams are the Avon, the Erme
and the Vealm, all running south. The Exe rises on Exmoor in
Somersetshire; but the main part of its course is through Devonshire
(where it gives name to Exeter), and it is joined on its way to the
English Channel by the lesser streams of the Culm, the Creedy and the
Clyst. The Otter, rising on the Blackdown Hills, also runs south, and
the Axe, for part of its course, divides the counties of Devon and
Dorset. These eastern streams are comparatively slow; while the rivers
of Dartmoor have a shorter and more rapid course.
_Geology._--The greatest area occupied by any one group of rocks in
Devonshire is that covered by the Culm, a series of slates, grits and
greywackes, with some impure limestones and occasional radiolarian
cherts as at Codden Hill; beds of "culm," an impure variety of coal,
are found at Bideford and elsewhere. This series of rocks occurs at
Bampton, Exeter and Chudleigh and extends thence to the western
boundary. North and south of the Culm an older series of slates, grits
and limestones appears; it was considered so characteristic of the
county that it was called the DEVONIAN SYSTEM (q.v.), the marine
equivalent of the Old Red Sandstone of Hereford and Scotland. It lies
in the form of a trough with its axis running east and west. In the
central hollow the Culm reposes, while the northern and southern rims
rise to the surface respectively north of the latitude of Barnstaple
and South Molton and south of the latitude of Tavistock. These
Devonian rocks have been subdivided into upper, middle and lower
divisions, but the stratigraphy is difficult to follow as the beds
have suffered much crumpling; fine examples of contorted strata may be
seen almost anywhere on the north coast, and in the south, at Bolt
Head and Start Point they have undergone severe metamorphism.
Limestones are only poorly developed in the north, but in the south
important masses occur, in the middle and at the base of the upper
subdivisions, about Plymouth, Torquay, Brixham and between Newton
Abbot and Totnes. Fossil corals abound in these limestones, which are
largely quarried and when polished are known as Devonshire marbles.
On the eastern side of the county is found an entirely different set
of rocks which cover the older series and dip away from them gently
towards the east. The lower and most westerly situated members of the
younger rocks is a series of breccias, conglomerates, sandstones and
marls which are probably of lower Bunter age, but by some geologists
have been classed as Permian. These red rocks are beautifully exposed
on the coast by Dawlish and Teignmouth, and they extend inland,
producing a red soil, past Exeter and Tiverton. A long narrow strip of
the same formation reaches out westward on the top of the Culm as far
as Jacobstow. Farther east, the Bunter pebble beds are represented by
the well-known pebble deposit of Budleigh Salterton, whence they are
traceable inland towards Rockbeare. These are succeeded by the Keuper
marls and sandstones, well exposed at Sidmouth, where the upper
Greensand plateau is clearly seen to overlie them. The Greensand
covers all the high ground northward from Sidmouth as far as the
Blackdown Hills. At Beer Head and Axmouth the Chalk is seen, and at
the latter place is a famous landslip on the coast, caused by the
springs which issue from the Greensand below the Chalk. The Lower
Chalk at Beer has been mined for building stone and was formerly in
considerable demand. At the extreme east of the county, Rhaetic and
Lias beds make their appearance, the former with a "bone" bed bearing
the remains of saurians and fish.
Dartmoor is a mass of granite that was intruded into the Culm and
Devonian strata in post-Carboniferous times and subsequently exposed
by denudation. Evidences of Devonian volcanic activity are abundant in
the masses of diabase, dolerite, &c., at Bradford and Trusham, south
of Exeter, around Plymouth and at Ashprington. Perhaps the most
interesting is the Carboniferous volcano of Brent Tor near Tavistock.
An Eocene deposit, the product of the denudation of the Dartmoor
Hills, lies in a small basin at Bovey Tracey (see BOVEY BEDS); it
yields beds of lignite and valuable clays.
Raised beaches occur at Hope's Nose and the Thatcher Stone near
Torquay and at other points, and a submerged forest lies in the bay
south of the same place. The caves and fissures in the Devonian
limestone at Kent's Hole near Torquay, Brixham and Oreston are famous
for the remains of extinct mammals; bones of the elephant, rhinoceros,
bear and hyaena have been found as well as flint implements of early
man.
_Minerals._--Silver-lead was formerly worked at Combe Martin near the
north coast, and elsewhere. Tin has been worked on Dartmoor (in stream
works) from an unknown period. Copper was not much worked before the
end of the 18th century. Tin occurs in the granite of Dartmoor, and
along its borders, but rather where the Devonian than where the
Carboniferous rocks border the granite. It is found most plentifully
in the district which surrounds Tavistock, which, for tin and other
ores, is in effect the great mining district of the county. Here,
about 4 m. from Tavistock, are the Devon Great Consols mines, which
from 1843 to 1871 were among the richest copper mines in the world,
and by far the largest and most profitable in the kingdom. The divided
profits during this period amounted to £1,192,960. But the mining
interests of Devonshire are affected by the same causes, and in the
same way, as those of Cornwall. The quantity of ore has greatly
diminished, and the cost of raising it from the deep mines prevents
competition with foreign markets. In many mines tin underlies the
general depth of the copper, and is worked when the latter has been
exhausted. The mineral products of the Tavistock district are various,
and besides tin and copper, ores of zinc and iron are largely
distributed. Great quantities of refined arsenic have been produced at
the Devon Great Consols mine, by elimination from the iron pyrites
contained in the various lodes. Manganese occurs in the neighbourhood
of Exeter, in the valley of the Teign and in N. Devon; but the most
profitable mines, which are shallow, are, like those of tin and
copper, in the Tavistock district.
The other mineral productions of the county consist of marbles,
building stones, slates and potters' clay. Among building stones, the
granite of Dartmoor holds the foremost place. It is much quarried near
Princetown, near Moreton Hampstead on the N.E. of Dartmoor and
elsewhere. The annual export is considerable. Hard traps, which occur
in many places, are also much used, as are the limestones of
Buckfastleigh and of Plymouth. The Roborough stone, used from an early
period in Devonshire churches, is found near Tavistock, and is a hard,
porphyritic elvan, taking a fine polish. Excellent roofing slates
occur in the Devonian series round the southern part of Dartmoor. The
chief quarries are near Ashburton and Plymouth (Cann quarry). Potters'
clay is worked at King's Teignton, whence it is largely exported; at
Bovey Tracey; and at Watcombe near Torquay. The Watcombe clay is of
the finest quality. China clay or kaolin is found on the southern side
of Dartmoor, at Lee Moor, and near Trowlesworthy. There is a large
deposit of umber close to Ashburton.
_Climate and Agriculture._--The climate varies greatly in different
parts of the county, but everywhere it is more humid than that of the
eastern or south-eastern parts of England. The mean annual temperature
somewhat exceeds that of the midlands, but the average summer heat is
rather less than that of the southern counties to the east. The air of
the Dartmoor highlands is sharp and bracing. Mists are frequent, and
snow often lies long. On the south coast frost is little known, and many
half hardy plants, such as hydrangeas, myrtles, geraniums and
heliotropes, live through the winter without protection. The climate of
Sidmouth, Teignmouth, Torquay and other watering places on this coast is
very equable, the mean temperature in January being 43.6° at Plymouth.
The north coast, exposed to the storms and swell of the Atlantic, is
more bracing; although there also, in the more sheltered nooks (as at
Combe Martin), myrtles of great size and age flower freely, and produce
their annual crop of berries.
Rather less than three-quarters of the total area of the county is under
cultivation; the cultivated area falling a little below the average of
the English counties. There are, however, about 160,000 acres of hill
pasture in addition to the area in permanent pasture, which is more than
one-half that of the cultivated area. The Devon breed of cattle is well
adapted both for fattening and for dairy purposes; while sheep are kept
in great numbers on the hill pastures. Devonshire is one of the chief
cattle-farming and sheep-farming counties. It is specially famous for
two products of the dairy--the clotted cream to which it gives its name,
and junket. Of the area under grain crops, oats occupy about three times
the acreage under wheat or barley. The bulk of the acreage under green
crops is occupied by turnips, swedes and mangold. Orchards occupy a
large acreage, and consist chiefly of apple-trees, nearly every farm
maintaining one for the manufacture of cider.
_Fisheries._--Though the fisheries of Devon are less valuable than those
of Cornwall, large quantities of the pilchard and herrings caught in
Cornish waters are landed at Plymouth. Much of the fishing is carried on
within the three-mile limit; and it may be asserted that trawling is the
main feature of the Devonshire industry, whereas seining and driving
characterize that of Cornwall. Pilchard, cod, sprats, brill, plaice,
soles, turbot, shrimps, lobsters, oysters and mussels are met with,
besides herring and mackerel, which are fairly plentiful. After
Plymouth, the principal fishing station is at Brixham, but there are
lesser stations in every bay and estuary.
_Other Industries._--The principal industrial works in the county are
the various Government establishments at Plymouth and Devonport. Among
other industries may be noted the lace-works at Tiverton; the
manufacture of pillow-lace for which Honiton and its neighbourhood has
long been famous; and the potteries and terra-cotta works of Bovey
Tracey and Watcombe. Woollen goods and serges are made at Buckfastleigh
and Ashburton, and boots and shoes at Crediton. Convict labour is
employed in the direction of agriculture, quarrying, &c., in the great
prison of Dartmoor.
_Communications._--The main line of the Great Western railway, entering
the county in the east from Taunton, runs to Exeter, skirts the coast as
far as Teignmouth, and continues a short distance inland by Newton Abbot
to Plymouth, after which it crosses the estuary of the Tamar by a great
bridge to Saltash in Cornwall. Branches serve Torquay and other seaside
resorts of the south coast; and among other branches are those from
Taunton to Barnstaple and from Plymouth northward to Tavistock and
Launceston. The main line of the London & South-Western railway between
Exeter and Plymouth skirts the north and west of Dartmoor by Okehampton
and Tavistock. A branch from Yeoford serves Barnstaple, Ilfracombe,
Bideford and Torrington, while the Lynton & Barnstaple and the Bideford,
Westward Ho & Appledore lines serve the districts indicated by their
names. The branch line to Princetown from the Plymouth-Tavistock line of
the Great Western company in part follows the line of a very early
railway--that constructed to connect Plymouth with the Dartmoor prison
in 1819-1825, which was worked with horse cars. The only waterways of
any importance are the Tamar, which is navigable up to Gunnislake (3 m.
S.W. of Tavistock), and the Exeter ship canal, noteworthy as one of the
oldest in England, for it was originally cut in the reign of Elizabeth.
_Population and Administration._--The area of the ancient county is
1,667,154 acres, with a population in 1891 of 631,808, and 1901 of
661,314. The area of the administrative county is 1,671,168 acres. The
county contains 33 hundreds. The municipal boroughs are Barnstaple (pop.
14,137), Bideford (8754), Dartmouth (6579), Devonport, a county borough
(70,437), Exeter, a city and county borough (47,185), Torrington,
officially Great Torrington (3241), Honiton (3271), Okehampton (2569),
Plymouth, a county borough (107,636), South Molton (2848), Tiverton
(10,382), Torquay (33,625), Totnes (4035). The other urban districts are
Ashburton (2628), Bampton (1657), Brixham (8092), Buckfastleigh (2520),
Budleigh Salterton (1883), Crediton (3974), Dawlish (4003), East
Stonehouse (15,111), Exmouth (10,485), Heavitree (7529), Holsworthy
(1371), Ilfracombe (8557), Ivybridge (1575), Kingsbridge (3025), Lynton
(1641), Newton Abbot (12,517), Northam (5355), Ottery St Mary (3495),
Paignton (8385), Salcombe (1710), Seaton (1325), Sidmouth (4201),
Tavistock (4728), Teignmouth (8636). The county is in the western
circuit, and assizes are held at Exeter. It has one court of quarter
sessions, and is divided into twenty-four petty sessional divisions. The
boroughs of Barnstaple, Bideford, Devonport, Exeter, Plymouth, South
Molton, and Tiverton have separate commissions of the peace and courts
of quarter sessions, and those of Dartmouth, Great Torrington, Torquay
and Totnes have commissions of the peace only. There are 461 civil
parishes. Devonshire is in the diocese of Exeter, with the exception of
small parts in those of Salisbury and Truro; and there are 516
ecclesiastical parishes or districts wholly or in part within the
county. The parliamentary divisions are the Eastern or Honiton,
North-eastern or Tiverton, Northern or South Molton, North-western or
Barnstaple, Western or Tavistock, Southern or Totnes, Torquay, and Mid
or Ashburton, each returning one member; and the county also contains
the parliamentary boroughs of Devonport and Plymouth, each returning two
members, and that of Exeter, returning one member.
_History._--The Saxon conquest of Devonshire must have begun some time
before the 8th century, for in 700 there existed at Exeter a famous
Saxon school. By this time, however, the Saxons had become Christians,
and established their supremacy, not by destructive inroads, but by a
gradual process of colonization, settling among the native Welsh and
allowing them to hold lands under equal laws. The final incorporation of
the district which is now Devonshire with the kingdom of Wessex must
have taken place about 766, but the county, and even Exeter, remained
partly Welsh until the time of Æthelstan. At the beginning of the 9th
century Wessex was divided into definite _pagi_, probably corresponding
to the later shires, and the Saxon Chronicle mentions Devonshire by name
in 823, when a battle was fought between the Welsh in Cornwall and the
people of Devonshire at Camelford. During the Danish invasions of the
9th century aldermen of Devon are frequently mentioned. In 851 the
invaders were defeated by the fyrd and aldermen of Devon, and in 878,
when the Danes under Hubba were harrying the coast with a squadron of
twenty-three ships, they were again defeated with great slaughter by the
fyrd. The modern hundreds of Devonshire correspond in position very
nearly with those given in the Domesday Survey, though the names have in
many cases been changed, owing generally to alterations in their places
of meeting. The hundred of Bampton formerly included estates west of the
Exe, now transferred to the hundred of Witheridge. Ten of the modern
hundreds have been formed by the union of two or more Domesday hundreds,
while the Domesday hundred of Liston has had the new hundred of
Tavistock severed from it since 1114. Many of the hundreds were
separated by tracts of waste and forest land, of which Devonshire
contained a vast extent, until in 1204 the inhabitants paid 5000 marks
to have the county disafforested, with the exception only of Dartmoor
and Exmoor.
Devonshire in the 7th century formed part of the vast bishopric of
Dorchester-on-Thames. In 705 it was attached to the newly created
diocese of Sherborne, and in 910 Archbishop Plegmund constituted
Devonshire a separate diocese, and placed the see at Crediton. About
1030 the dioceses of Devonshire and Cornwall were united, and in 1049
the see was fixed at Exeter. The archdeaconries of Exeter, Barnstaple
and Totnes are all mentioned in the 12th century and formerly comprised
twenty-four deaneries. The deaneries of Three Towns, Collumpton and
Ottery have been created since the 16th century, while those of
Tamerton, Dunkeswell, Dunsford and Plymptre have been abolished,
bringing the present number to twenty-three.
At the time of the Norman invasion Devonshire showed an active hostility
to Harold, and the easy submission which it rendered to the Conqueror
accounts for the exceptionally large number of Englishmen who are found
retaining lands after the Conquest. The many vast fiefs held by Norman
barons were known as honours, chief among them being Plympton,
Okehampton, Barnstaple, Harberton and Totnes. The honour of Plympton was
bestowed in the 12th century on the Redvers family, together with the
earldom of Devon; in the 13th century it passed to the Courtenay family,
who had already become possessed of the honour of Okehampton, and who in
1335 obtained the earldom. The dukedom of Exeter was bestowed in the
14th century on the Holland family, which became extinct in the reign of
Edward IV. The ancestors of Sir Walter Raleigh, who was born at
Budleigh, had long held considerable estates in the county.
Devonshire had an independent sheriff, the appointment being at first
hereditary, but afterwards held for one year only. In 1320 complaint was
made that all the hundreds of Devonshire were in the hands of the great
lords, who did not appoint a sufficiency of bailiffs for their proper
government. The miners of Devon had independent courts, known as
stannary courts, for the regulation of mining affairs, the four stannary
towns being Tavistock, Ashburton, Chagford, and Plympton. The ancient
miners' parliament was held in the open air at Crockern's Tor.
The castles of Exeter and Plympton were held against Stephen by Baldwin
de Redvers, and in the 14th and 15th centuries the French made frequent
attacks on the Devonshire coast, being repulsed in 1404 by the people of
Dartmouth. In the Wars of the Roses the county was much divided, and
frequent skirmishes took place between the earl of Devon and Lord
Bonville, the respective champions of the Lancastrian and Yorkist
parties. Great disturbances in the county followed the Reformation of
the 16th century and in 1549 a priest was compelled to say mass at
Sampford Courtney. On the outbreak of the Civil War the county as a
whole favoured the parliament, but the prevailing desire was for peace,
and in 1643 a treaty for the cessation of hostilities in Devonshire and
Cornwall was agreed upon. Skirmishes, however, continued until the
capture of Dartmouth and Exeter in 1646 put an end to the struggle. In
1688 the prince of Orange landed at Torbay and was entertained for
several days at Ford and at Exeter.
The tin mines of Devon have been worked from time immemorial, and in the
14th century mines of tin, copper, lead, gold and silver are mentioned.
Agriculturally the county was always poor, and before the
disafforestation rendered especially so through the ravages committed by
the herds of wild deer. At the time of the Domesday Survey the salt
industry was important, and there were ninety-nine mills in the county
and thirteen fisheries. From an early period the chief manufacture was
that of woollen cloth, and a statute 4 Ed. IV. permitted the manufacture
of cloths of a distinct make in certain parts of Devonshire. About 1505
Anthony Bonvis, an Italian, introduced an improved method of spinning
into the county, and cider-making is mentioned in the 16th century. In
1680 the lace industry was already flourishing at Colyton and Ottery St
Mary, and flax, hemp and malt were largely produced in the 17th and 18th
centuries.
Devonshire returned two members to parliament in 1290, and in 1295
Barnstaple, Exeter, Plympton, Tavistock, Torrington and Totnes were also
represented. In 1831 the county with its boroughs returned a total of
twenty-six members, but under the Reform Act of 1832 it returned four
members in two divisions, and with ten boroughs was represented by a
total of eighteen members. Under the act of 1868 the county returned six
members in three divisions, and four of the boroughs were disfranchised,
making a total of seventeen members.
_Antiquities._--In primeval antiquities Devonshire is not so rich as
Cornwall; but Dartmoor abounds in remains of the highest interest, the
most peculiar of which are the long parallel alignments of upright
stones, which, on a small scale, resemble those of Carnac in Brittany.
On Dartmoor the lines are invariably straight, and are found in direct
connexion with cairns, and with circles which are probably sepulchral.
These stone avenues are very numerous. Of the so-called sacred circles
the best examples are the "Longstones" on Scorhill Down, and the "Grey
Wethers" under Sittaford Tor. By far the finest cromlech is the
"Spinster's Rock" at Drewsteignton, a three-pillared cromlech which may
well be compared with those of Cornwall. There are numerous menhirs or
single upright stones; a large dolmen or holed stone lies in the bed of
the Teign, near the Scorhill circle; and rock basins occur on the summit
of nearly every tor on Dartmoor (the largest are on Kestor, and on
Heltor, above the Teign). It is, however, tolerably evident that these
have been produced by the gradual disintegration of the granite, and
that the dolmen in the Teign is due to the action of the river. Clusters
of hut foundations, circular, and formed of rude granite blocks, are
frequent; the best example of such a primitive village is at Batworthy,
near Chagford; the type resembles that of East Cornwall. Walled
enclosures, or pounds, occur in many places; Grimspound is the most
remarkable. Boundary lines, also called trackways, run across Dartmoor
in many directions; and the rude bridges, formed of great slabs of
granite, deserve notice. All these remains are on Dartmoor. Scattered
over the county are numerous large hill castles and camps,--all
earthworks, and all apparently of the British period. Roman relics have
been found from time to time at Exeter (_Isca Damnoniorum_), the only
large Roman station in the county.
The churches are for the most part of the Perpendicular period, dating
from the middle of the 14th to the end of the 15th century. Exeter
cathedral is of course an exception, the whole (except the Norman
towers) being very beautiful Decorated work. The special features of
Devonshire churches, however, are the richly carved pulpits and chancel
screens of wood, in which this county exceeded every other in England,
with the exception of Norfolk and Suffolk. The designs are rich and
varied, and the skill displayed often very great. Granite crosses are
frequent, the finest and earliest being that of Coplestone, near
Crediton. Monastic remains are scanty; the principal are those at Tor,
Buckfast, Tavistock and Buckland Abbeys. Among domestic buildings the
houses of Wear Gilford, Bradley and Dartington of the 15th century;
Bradfield and Holcombe Rogus (Elizabethan), and Forde (Jacobean),
deserve notice. The ruined castles of Okehampton (Edward I.), Exeter,
with its vast British earthworks, Berry Pomeroy (Henry III., with ruins
of a large Tudor mansion), Totnes (Henry III.) and Compton (early 15th
century), are all interesting and picturesque.
AUTHORITIES.--T. Westcote, _Survey of Devon_, written about 1630, and
first printed in 1845; J. Prince, _Worthies of Devon_ (Exeter, 1701);
Sir W. Pole, _Collections towards a History of the County of Devon_
(London, 1791); R. Polwhele, _History of Devonshire_ (3 vols. Exeter,
1797, 1798-1800); T. Moore, _History of Devon from the Earliest Period
to the Present Time_ (vols, i., ii., London, 1829-1831); G. Oliver,
_Historic Collections relating to the Monasteries in Devon_ (Exeter,
1820); D. and S. Lysons, _Magna Britannia_ (vol. vi., London, 1822);
_Ecclesiastical Antiquities in Devon_ (Exeter, 1844); Mrs Bray,
_Traditions of Devonshire_, in a series of letters to Robert Southey
(London, 1838); G. C. Boase, _Devonshire Bibliography_ (London, 1883);
Sir W. R. Drake, _Devonshire Notes and Notelets_ (London, 1888); S.
Hewett, _Peasant Speech of Devon_ (London, 1892); R. N. Worth,
_History of Devonshire_ (London, 1886, new edition, 1895); C. Worthy,
_Devonshire Parishes_ (Exeter, 1887); _Devonshire Wills_ (London,
1896); _Victoria County History, Devonshire_.
DEVRIENT, the name of a family of German actors.
LUDWIG DEVRIENT (1784-1832), born in Berlin on the 15th of December
1784, was the son of a silk merchant. He was apprenticed to an
upholsterer, but, suddenly leaving his employment, joined a travelling
theatrical company, and made his first appearance on the stage at Gera
in 1804 as the messenger in Schiller's _Braut von Messina_. By the
interest of Count Brühl, he appeared at Rudolstadt as Franz Moor in
Schiller's _Räuber_, so successfully that he obtained a permanent
engagement at the ducal theatre in Dessau, where he played until 1809.
He then received a call to Breslau, where he remained for six years. So
brilliant was his success in the title-parts of several of Shakespeare's
plays, that Iffland began to fear for his own reputation; yet that great
artist was generous enough to recommend the young actor as his only
possible successor. On Iffland's death Devrient was summoned to Berlin,
where he was for fifteen years the popular idol. He died there on the
30th of December 1832. Ludwig Devrient was equally great in comedy and
tragedy. Falstaff, Franz Moor, Shylock, King Lear and Richard II. were
among his best parts. Karl von Holtei in his _Reminiscences_ has given a
graphic picture of him and the "demoniac fascination" of his acting.
See Z. Funck, _Aus dem Leben zweier Schauspieler, Ifflands und
Devrients_ (Leipzig, 1838); H. Smidt in _Devrient-Novellen_ (3rd ed.,
Berlin, 1882); R. Springer in the novel _Devrient und Hoffmann_
(Berlin, 1873), and Eduard Devrient's _Geschichte der deutschen
Schauspielkunst_ (Leipzig, 1861).
Three of the nephews of Ludwig Devrient, sons of his brother, a
merchant, were also connected with the stage. KARL AUGUST DEVRIENT
(1797-1872) was born at Berlin on the 5th of April 1797. After being for
a short time in business, he entered a cavalry regiment as volunteer and
fought at Waterloo. He then joined the stage, making his first
appearance on the stage in 1819 at Brunswick. In 1821 he received an
engagement at the court theatre in Dresden, where, in 1823, he married
Wilhelmine Schröder (see SCHRÖDER-DEVRIENT). In 1835 he joined the
company at Karlsruhe, and in 1839 that at Hanover. His best parts were
Wallenstein and King Lear. He died on the 5th of April 1872. His brother
PHILIPP EDUARD DEVRIENT (1801-1877), born at Berlin on the 11th of
August 1801, was for a time an opera singer. Turning his attention to
theatrical management, he was from 1844 to 1846 director of the court
theatre in Dresden. Appointed to Karlsruhe in 1852, he began a thorough
reorganization of the theatre, and in the course of seventeen years of
assiduous labour, not only raised it to a high position, but enriched
its repertory by many noteworthy librettos, among which _Die Gunst des
Augenblicks_ and _Verirrungen_ are the best known. But his chief work is
his history of the German stage--_Geschichte der deutschen
Schauspielkunst_ (Leipzig, 1848-1874). He died on the 4th of October
1877. A complete edition of his works--_Dramatische und dramaturgische
Schriften_--was published in ten volumes (Leipzig, 1846-1873).
The youngest and the most famous of the three nephews of Ludwig Devrient
was GUSTAV EMIL DEVRIENT (1803-1872), born in Berlin on the 4th of
September 1803. He made his first appearance on the stage in 1821, at
Brunswick, as Raoul in Schiller's _Jungfrau von Orleans_. After a short
engagement in Leipzig, he received in 1829 a call to Hamburg, but after
two years accepted a permanent appointment at the court theatre in
Dresden, to which he belonged until his retirement in 1868. His chief
characters were Hamlet, Uriel Acosta (in Karl Gutzkow's play), Marquis
Posa (in Schiller's _Don Carlos_), and Goethe's Torquato Tasso. He acted
several times in London, where his Hamlet was considered finer than
Kemble's or Edmund Kean's. He died on the 7th of August 1872.
OTTO DEVRIENT (1838-1894), another actor, born in Berlin on the 3rd of
October 1838, was the son of Philipp Eduard Devrient. He joined the
stage in 1856 at Karlsruhe, and acted successively in Stuttgart, Berlin
and Leipzig, until he received a fixed appointment at Karlsruhe, in
1863. In 1873 he became stage manager at Weimar, where he gained great
praise for his _mise en scène_ of Goethe's _Faust_. After being manager
of the theatres in Mannheim and Frankfort he retired to Jena, where in
1883 he was given the honorary degree of doctor of philosophy. In 1884
he was appointed director of the court theatre in Oldenburg, and in
1889 director of dramatic plays in Berlin. He died at Stettin on the
23rd of June 1894.
DEW. The word "dew" (O.E. _deaw_; cf. Ger. _Tau_) is a very ancient one
and its meaning must therefore be defined on historical principles.
According to the _New English Dictionary_, it means "the moisture
deposited in minute drops upon any cool surface by condensation of the
vapour of the atmosphere; formed after a hot day, during or towards
night and plentiful in the early morning." Huxley in his _Physiography_
makes the addition "without production of mist." The formation of mist
is not necessary for the formation of dew, nor does it necessarily
prevent it. If the deposit of moisture is in the form of ice instead of
water it is called hoarfrost. The researches of Aitken suggest that the
words "by condensation of the vapour in the atmosphere" might be omitted
from the definition. He has given reasons for believing that the large
dewdrops on the leaves of plants, the most characteristic of all the
phenomena of dew, are to be accounted for, in large measure at least, by
the exuding of drops of water from the plant through the pores of the
leaves themselves. The formation of dewdrops in such cases is the
continuation of the irrigation process of the plant for supplying the
leaves with water from the soil. The process is set up in full vigour in
the daytime to maintain tolerable thermal conditions at the surface of
the leaf in the hot sun, and continued after the sun has gone.
On the other hand, the most typical physical experiment illustrating the
formation of dew is the production of a deposit of moisture, in minute
drops, upon the exterior surface of a glass or polished metal vessel by
the cooling of a liquid contained in the vessel. If the liquid is water,
it can be cooled by pieces of ice; if volatile like ether, by bubbling
air through it. No deposit is formed by this process until the
temperature is reduced to a point which, from that circumstance, has
received a special name, although it depends upon the state of the air
round the vessel. So generally accepted is the physical analogy between
the natural formation of dew and its artificial production in the manner
described, that the point below which the temperature of a surface must
be reduced in order to obtain the deposit is known as the "dew-point."
In the view of physicists the dew-point is the temperature at which, _by
being cooled without change of pressure_, the air becomes saturated with
water vapour, not on account of any increase of supply of that compound,
but by the diminution of the capacity of the air for holding it in the
gaseous condition. Thus, when the dew-point temperature has been
determined, the pressure of water vapour in the atmosphere at the time
of the deposit is given by reference to a table of saturation pressures
of water vapour at different temperatures. As it is a well-established
proposition that the pressure of the water vapour in the air does not
vary while the air is being cooled without change of its total external
pressure, the saturation pressure at the dew-point gives the pressure of
water vapour in the air when the cooling commenced. Thus the artificial
formation of dew and consequent determination of the dew-point is a
recognized method of measuring the pressure, and thence the amount of
water vapour in the atmosphere. The dew-point method is indeed in some
ways a fundamental method of hygrometry.
The dew-point is a matter of really vital consequence in the question of
the oppressiveness of the atmosphere or its reverse. So long as the
dew-point is low, high temperature does not matter, but when the
dew-point begins to approach the normal temperature of the human body
the atmosphere becomes insupportable.
The physical explanation of the formation of dew consists practically in
determining the process or processes by which leaves, blades of grass,
stones, and other objects in the open air upon which dew may be
observed, become cooled "below the dew-point."
Formerly, from the time of Aristotle at least, dew was supposed to
"fall." That view of the process was not extinct at the time of
Wordsworth and poets might even now use the figure without reproach. To
Dr Charles Wells of London belongs the credit of bringing to a focus the
ideas which originated with the study of radiation at the beginning of
the 19th century, and which are expressed by saying that the cooling
necessary to produce dew on exposed surfaces is to be attributed to the
radiation from the surfaces to a clear sky. He gave an account of the
theory of automatic cooling by radiation, which has found a place in all
text-books of physics, in his first _Essay on Dew_ published in 1818.
The theory is supported in that and in a second essay by a number of
well-planned observations, and the essays are indeed models of
scientific method. The process of the formation of dew as represented by
Wells is a simple one. It starts from the point of view that all bodies
are constantly radiating heat, and cool automatically unless they
receive a corresponding amount of heat from other bodies by radiation or
conduction. Good radiators, which are at the same time bad conductors of
heat, such as blades of grass, lose heat rapidly on a clear night by
radiation to the sky and become cooled below the dew-point of the
atmosphere.
The question was very fully studied by Melloni and others, but little
more was added to the explanation given by Wells until 1885, when John
Aitken of Falkirk called attention to the question whether the water of
dewdrops on plants or stones came from the air or the earth, and
described a number of experiments to show that under the conditions of
observation in Scotland, it was the earth from which the moisture was
probably obtained, either by the operation of the vascular system of
plants in the formation of exuded dewdrops, or by evaporation and
subsequent condensation in the lowest layer of the atmosphere. Some
controversy was excited by the publication of Aitken's views, and it is
interesting to revert to it because it illustrates a proposition which
is of general application in meteorological questions, namely, that the
physical processes operative in the evolution of meteorological
phenomena are generally complex. It is not radiation alone that is
necessary to produce dew, nor even radiation from a body which does not
conduct heat. The body must be surrounded by an atmosphere so fully
supplied with moisture that the dew-point can be passed by the cooling
due to radiation. Thus the conditions favourable for the formation of
dew are (1) a good radiating surface, (2) a still atmosphere, (3) a
clear sky, (4) thermal insulation of the radiating surface, (5) warm
moist ground or some other provision to produce a supply of moisture in
the surface layers of air.
Aitken's contribution to the theory of dew shows that in considering the
supply of moisture we must take into consideration the ground as well as
the air and concern ourselves with the temperature of both. Of the five
conditions mentioned, the first four may be considered necessary, but
the fifth is very important for securing a copious deposit. It can
hardly be maintained that no dew could form unless there were a supply
of water by evaporation from warm ground, but, when such a supply is
forthcoming, it is evident that in place of the limited process of
condensation which deprives the air of its moisture and is therefore
soon terminable, we have the process of distillation which goes on as
long as conditions are maintained. This distinction is of some practical
importance for it indicates the protecting power of wet soil in favour
of young plants as against night frost. If distillation between the
ground and the leaves is set up, the temperature of the leaves cannot
fall much below the original dew-point because the supply of water for
condensation is kept up; but if the compensation for loss of heat by
radiation is dependent simply on the condensation of water from the
atmosphere, without renewal of the supply, the dew-point will gradually
get lower as the moisture is deposited and the process of cooling will
go on.
In these questions we have to deal with comparatively large changes
taking place within a small range of level. It is with the layer a few
inches thick on either side of the surface that we are principally
concerned, and for an adequate comprehension of the conditions close
consideration is required. To illustrate this point reference may be
made to figs. 1 and 2, which represent the condition of affairs at 10.40
P.M. on about the 20th of October 1885, according to observations by
Aitken. Vertical distances represent heights in feet, while the
temperatures of the air and the dew-point are represented by horizontal
distances and their variations with height by the curved lines of the
diagram. The line marked 0 is the ground level itself, a rather
indefinite quantity when the surface is grass. The whole vertical
distance represented is from 4 ft. above ground to 1 ft. below ground,
and the special phenomena which we are considering take place in the
layer which represents the rapid transition between the temperature of
the ground 3 in. below the surface and that of the air a few inches
above ground.
[Illustration: FIG. 1.]
[Illustration: FIG. 2.]
The point of interest is to determine where the dew-point curve and
dry-bulb curve will cut. If they cut above the surface, mist will
result; if they cut at the surface, dew will be formed. Below the
surface, it may be assumed that the air is saturated with moisture and
any difference in temperature of the dew-point is accompanied by
distillation. It may be remarked, by the way, that such distillation
between soil layers of different temperatures must be productive of the
transference of large quantities of water between different levels in
the soil either upward or downward according to the time of year.
These diagrams illustrate the importance of the warmth and moisture of
the ground in the phenomena which have been considered. From the surface
there is a continual loss of heat going on by radiation and a continual
supply of warmth and moisture from below. But while the heat can escape,
the moisture cannot. Thus the dry-bulb line is deflected to the left as
it approaches the surface, the dew-point line to the right. Thus the
effect of the moisture of the ground is to cause the lines to approach.
In the case of grass, fig. 2, the deviation of the dry-bulb line to the
left to form a sharp minimum of temperature at the surface is well
shown. The dew-point line is also shown diverted to the left to the same
point as the dry-bulb; but that could only happen if there were so
copious a condensation from the atmosphere as actually to make the air
drier at the surface than up above. In diagram 1, for soil, the effect
on air temperature and moisture is shown; the two lines converge to cut
at the surface where a dew deposit will be formed. Along the underground
line there must be a gradual creeping of heat and moisture towards the
surface by distillation, the more rapid the greater the temperature
gradient.
The amount of dew deposited is considerable, and, in tropical countries,
is sometimes sufficiently heavy to be collected by gutters and spouts,
but it is not generally regarded as a large percentage of the total
rainfall. Loesche estimates the amount of dew for a single night on the
Loango coast at 3 mm., but the estimate seems a high one. Measurements
go to show that the depth of water corresponding with the aggregate
annual deposit of dew is 1 in. to 1.5 in. near London (G. Dines), 1.2
in. at Munich (Wollny), 0.3 in. at Montpellier (Crova), 1.6 in. at
Tenbury, Worcestershire (Badgley).
With the question of the amount of water collected as dew, that of the
maintenance of "dew ponds" is intimately associated. The name is given
to certain isolated ponds on the upper levels of the chalk downs of the
south of England and elsewhere. Some of these ponds are very ancient, as
the title of a work on _Neolithic Dewponds_ by A. J. and G. Hubbard
indicates. Their name seems to imply the hypothesis that they depend
upon dew and not entirely upon rain for their maintenance as a source of
water supply for cattle, for which they are used. The question has been
discussed a good deal, but not settled; the balance of evidence seems to
be against the view that dew deposits make any important contribution to
the supply of water. The construction of dew ponds is, however, still
practised on traditional lines, and it is said that a new dew pond has
first to be filled artificially. It does not come into existence by the
gradual accumulation of water in an impervious basin.