of the whole; while the author has made it the depository of a
variety of remarks and recommendations on this [p106] subject, very
particularly as it relates to the army. If he is correct,—and we
see no reason to doubt it, from the nature of the statements,—the
ignorance of this subject, even among the medical department of the
army, has been most extraordinary and most unaccountable; while if
Walcheren is proof enough of this, the writer before us has pointed
out facts enough to show that it was not a solitary case, while
evidently restrained by fear of some sort—we are almost inclined to
call it cowardice—from telling all that he might have told. And we do
think it wrong to retain or suppress that which is important to the
public safety, under a fear that the feelings of individuals may be
hurt; since the business of a writer is with justice and utility, and
the security or welfare of thousands is of infinitely greater moment
than the comforts of a few, and those also culpable.
Under this head, propagation, the author describes how this poison
is conveyed by the winds, while the facts add much to the number
and variety of the precautionary measures. And here also we find
a speculation of no small curiosity, respecting the East wind,
attempting to prove that wherever this is insalubrious or pernicious,
it arises from its being the vehicle of malaria; while attempting
also to prove that this substance can be conveyed from Holland to
the coasts of England in that wind. We shall not pretend to give an
opinion on this subject; and since the author himself has noticed
it in the paper printed in our present number, we shall suffer our
readers to form their own judgments respecting it.
One also of the most curious facts mentioned in this chapter, is the
singular limitation of malaria; and we must admit that the instance
quoted as to the Chatham road is so remarkable as to be almost
incredible; though, as we find that all the people agree in it, we
cannot pretend to say it is not a fact. Indeed the facts of this
nature, so familiar at Rome, are fully as inexplicable; so that all
we can conclude is, that we are ignorant of the philosophy of this
subject: no very great cause of surprise, unless it were proved that
we could explain every thing else which belongs to meteorology.
In the eighth chapter we have an explanation of the effects of
climate and seasons in the production of malaria; and while we
need not analyse the facts which it contains, we may introduce in
lieu of this, the explanations which its statements afford as to
that recent increase of the diseases of malaria which we noticed
at the commencement of this article. The last few years have been
distinguished for an [p107] uncommon prevalence of East winds, and
to such a degree indeed, that we can find no meteorological records
at all to be compared with the history of these years. And while the
history of the intermittent and remittent, in London at least, from
the time of Morton and Sydenham downwards, shows that all its periods
of such diseases have been periods of East winds, it is not difficult
to see how it acts as to both classes of marsh fever. To London,
in particular, it is the best conductor, propagating the malaria
from all the moist lands to the eastward. To the East coast, if our
author’s theory is valid, it brings the malaria from Holland; and,
moreover, as it forms our hottest summers, it causes our own climate
to approximate more to the southern ones, and thus enables our lands
to produce a greater quantity of malaria than in ordinary summers.
To pass from the eighth chapter, the ninth is a partial sketch of
the geography of malaria; a chapter for which the author apologises,
but which is nevertheless a very interesting collection of facts
on a subject where a volume is, doubtless, a desideratum. And it
would require a volume; while, in spite of our author’s fears, we
can really see no reason why such a statistical account of health
should not be drawn up for England, when the utility of it is
unquestionable. It is true that people cannot abandon their homes
or change their residences, because their lots happen to be cast in
an insalubrious country. But it is not less important to know what
and where these dangers are; because, though the inhabitants may be
compelled to abide, they can still correct much of the evil by the
various modes pointed out, or avoid much of the hazard by resorting
to the obvious precautions. To be ignorant, is to be exposed to the
full evil: to know where it lies, is to know how and where to avoid
it in numerous ways; since it will be found that by far the greater
number of diseases occurring, were not necessary or unavoidable, but
have been the result of ignorance as to the precise fact or spot
which did produce the effect in question. And this we conceive to
be the great use of the book before us; and that if ever it, or a
code of rules founded on it, shall become popular, or form a _vade
mecum_, particularly in the country, the effect will be to reduce
most materially the quantity of disease, and very particularly that
which is by far the most serious, the summer and autumnal fevers.
On this around, we should be glad to see a geography of malaria for
England; and we do hope that it will be undertaken by some person
of sufficient industry, and of more [p108] courage than our author;
while we cannot doubt that whoever attempts it would at least find it
a profitable speculation. With these remarks we must pass over this
chapter, as we could take no statement from it which would serve any
useful purpose; though, as far as it goes, it will form a very useful
guide to travellers on the continent of Europe, or to those who, as
emigrants, are in search of a residence abroad.
The tenth chapter examines the inquiries which have been instituted
into the chemical nature of malaria, leaving the question just where
it was. In fact we, as chemists, do not believe that this science is
yet in possession of the means required for analyses of this delicate
nature; but we see no reason whatever why it should be despaired of,
when chemistry has already, within a very few years, effected things
which seemed far more impracticable and hopeless.
The eleventh and last chapter contains an enumeration of the
diseases produced by malaria, presenting a most formidable list, and
absolutely making us shudder in some of the details which relate to
the worst parts of France and Italy. The representation here given
of the average of life in these districts is particularly striking;
while of the truth of all the facts, we can speak from personal
knowledge. Our author has also noticed the effect of this poison
on animals; showing that it is the cause of the noted epidemics in
cattle, and also of the rot in sheep. If he will look into Livy, he
will find a confirmation, which he appears to have passed by when
quoting that author for epidemic seasons: this being, that in the
same years in which epidemic “pestilences” appeared among the people,
there was also a great mortality among the cattle.
We do not know what his own profession will say of his attempt,
or rather proposal, to prove that the celebrated disease of the
nerves called Tic Douleureux is the produce of malaria and a mode of
intermittent fever; nor how they will receive his proposal to arrange
Sciatica and Rheumatic pains, with many other local diseases, under
this head. But this is not our affair: and as he has promised us two
other volumes, on all the diseases which are produced by malaria,
including these, we must wait with patience; knowing at least that he
is a dealer in facts and not in hypotheses, and expecting, that even
if he should fail to establish his point, he will try to do it, as
he has been used to do in the other sciences which he has attempted,
through the road of facts and evidence. [p109]
_An Account of a new Genus of Plants called_ REEVESIA. By John
Lindley, Esq., F.L.S., &c. &c.
In a collection of dried specimens of plants sent to the
Horticultural Society from China, by Mr. Reeves, are a few branches,
with flowers, of a remarkable genus which is at present undescribed,
but which is of so curious a nature, and of such importance with
reference to the determination of some natural affinities, that I
have thought it deserving immediate record; especially as drawings
of the fruit, which have been subsequently obtained from the same
indefatigable correspondent of the Society, render its history
tolerably complete.
The _branches_ appear to be fragments of an evergreen tree; they are
slender, rounded, and smooth. The _nascent gemmæ_ are covered with
a dense rufous pubescence. The _leaves_ are alternate, becoming,
towards the extremities of the branches, opposite by approximation;
their form is ovate-lanceolate acuminate, and in size they vary
from three inches to nearly six in length; the surface, even of
the youngest, is perfectly smooth on each side; their veins are
inconspicuous, the lowest pair of venæ primariæ being divergent at
an angle of about 40°, while the others spread outwards at an angle
of 55° or 60°; the venæ arcuatæ and externæ are obscurely seen,
but form together a number of rhomboidal spaces, equal in diameter
to nearly one third of each side of the leaf; the proportion borne
by the petiole to the lamina is variable, sometimes equalling
one-fourth of the length of the latter, and not unfrequently being
less than one-sixth of its length: this proportion not depending
upon the station of the leaves; the petiole is smooth, half-round,
and thickened at the extremity, where it unites with the lamina.
_Stipulæ_ are none. The _flowers_ are greenish-white, in terminal
thyrsoid compound racemes; the upper part of the _rachis_, and of
its branches, is slightly protected by stellate pubescence; the
_pedicles_ are closely covered with pubescence of the same nature,
and have one subulate downy deciduous bracteola at the base, and
another towards the apex. The _calyx_ is inferior, campanulate,
tapering a little towards the base, densely clothed with stellate
pubescence, bursting irregularly at the apex into [p110] four or
five ovate teeth, which are somewhat imbricated during æstivation,
but which are separated by the growth of the petals long before
the expansion of the flower; the veins of the calyx are remarkably
reticulated, and when cut, a considerable quantity of mucilaginous
viscid fluid is exuded. The _petals_ are whitish-green, hypogynous,
with a convolute æstivation; their _ungues_ are spatulate, and as
long as the calyx; their _laminæ_ oblong, spreading flat, and then
overlapping each other at the base; at the point of separation of
the unguis and lamina is a small callus, and on each side a notch
upon the margin. The _stamens_ are seated upon a long, filiform,
subclavate, smooth torus; the _filaments_ are consolidated into a
capitate five-toothed cup, nearly closed at the orifice, and on
the outside of this cup are placed the _antheræ_, three to each
tooth; the latter are two-celled, with divaricating cells, which
open longitudinally, and are so entangled with each other that the
whole surface of the cup appears, when the antheræ have burst, to
consist of a single many-celled anthera. The _pollen_ is spherical
and smooth. he _ovarium_ is seated within the cup of stamens, and is
so entirely concealed that it cannot be discovered till some part of
the cup is removed by violence; it is ovate, smooth, and formed of
five inseparable cells, each of which has two ovula placed one above
the other, and attached to their placenta by their inner margin; the
_stigma_ is sessile, with five radiating lobes. From the Chinese
drawing, the half-ripe fruit appears to be fleshy, with five deep
angles, and five cells, without any remains of calyx, and with a
slight appearance of separation between the lobes. The ripe fruit
is an obovate, five-angled, five-celled, five-valved, retuse, woody
capsule, with a loculicidal dehiscence, and no separable axis. The
seeds are attached one to each side of the valves, and are expanded
at their lower end into a wing.
From this description it is obvious that, with the single exception
of the contents of the seed, we are in possession of all that it is
essential to know of the structure of this plant. The next subject of
consideration is its affinity.
The stellate pubescence, the thickening of the petiole at the point
where it expands into the lamina, the station of the stamens upon a
long, filiform torus, the external position of the [p111] antheræ,
and the union of the filaments by threes into a cup surrounding
the ovarium, are all characters that forcibly call to recollection
the genus Sterculia. The calyx, indeed, in that genus is generally
divided much more deeply than in the plant now under consideration,
and the antheræ are usually seated at the base of the ovarium;
but, on the other hand, in Sterculia colorata of Roxburgh, which,
if a distinct genus, (ERYTHROPSIS) as I am inclined to believe; is
nevertheless next of kin to Sterculia, the calyx is of the same
figure and divided in the same degree, and the antheræ are also
combined in a capitate cup inclosing the ovarium. If, however, we
pursue this comparison further we find that, with the characters now
adverted to, the similarity ceases; in Sterculia there are no petals,
the calyx has a valvular not imbricate æstivation, the cells of the
fruit separate into distinct folliculi, and do not combine into a
solid woody capsule, and the seeds are destitute of wings.
The fruit suggests so obviously some affinity with Pterospermum,
that it is next necessary to institute a comparison with that
genus. Stellate pubescence, a calyx divided into five portions,
five hypogynous unguiculate petals, and fifteen fertile stamens
united into a cup, seated on a stipitiform torus, and surrounding
the ovarium, a five-celled ovarium, a woody five-celled capsule,
with a loculicidal dehiscence, no axis, and winged seeds; all these
characters are common to Pterospermum and our plant; but on the
other hand the points in which they differ are of much importance.
The æstivation of Pterospermum is valvate recurved not imbricate;
its calyx is five-parted, not four—five-toothed; its anthers have
parallel not divaricating cells, and are seated upon long distinct
filaments, not sessile, upon the outside of a capituliform cup; and
finally the petioles of the leaves are not connected with the lamina
by a thickened space. The seeds are also winged at the apex, not at
the base, but upon this point it is not my wish to insist.
If the comparison thus instituted with Pterospermum and Sterculia be
attentively considered, we cannot fail to remark that the subject of
these observations is nearly equally related to both; to Pterospermum
in its petals and fruit, to Sterculia in its calyx and stamens.
It must, therefore, be stationed between those two genera, thus
confirming the propriety of M. [p112] Kunth’s combination of the
Sterculiaceæ of Ventenat with the Byttneriaceæ of Mr. Brown; and, in
fact, breaking down every barrier between them.
There are many other points that will suggest themselves to the
Botanist, in which this plant is highly worthy of consideration, but
for the present it will be enough to give the botanical characters
with which it may stand recorded. It is named in honour of John
Reeves, Esq., now resident at Canton, to whom we are indebted for
our knowledge of it, from whose unwearied exertions in the cause of
science the botany of China has received material assistance, and to
whom our gardens are indebted for many of the fairest ornaments they
contain.
REEVESIA.
_Ord. Nat._ BYTTNERIACEÆ; _Sterculiam_ (_Erythropsin_) _inter et
terospermum_.
Calyx campanulatus, 5-dentatus, æstivatione imbricatâ, pube
stellatâ tomentosus, bracteolatus. Petala 5, hypogyna, unguiculata,
æstivatione convoluta, callo inter unguem et laminam. Stamina
in toro longo filiformi insidentia. Antheræ 15, sessiles, in
cyatho capituliformi, apice tantum pervio, obsoletè 5-dentato
connatæ, extrorsæ, biloculares, loculis divaricatis intricatis,
longitudinaliter dehiscentibus. Pollen sphæricum glabrum. Ovarium
sessile, intrà cyathum antheriferum, ovatum, glabrum, 5-angulare,
5-loculare, loculis dispermis. Ovula margini loculorum unum super
alterum affixa, superiore basi concavo in inferiorem incumbente.
Stigma 5-lobum, simplicissimum, sessile. Capsula stipitata, lignosa,
obovata, 5-angularis, 5-locularis, loculicidò 5-valvis, axi nullo.
Semina cuique loculo duo basi alata.——Arbor (Chinæ) foliis alternis
exstipulatis, racemis terminalibus compositis, floribus albis.
1. Reevesia thyrsoidea.
_Habitat_ in China (v. s. sp. in Herb. et iconem in Bibliotheca Soc.
Hort.)
[p113]
ASTRONOMICAL AND NAUTICAL COLLECTIONS.
i. _Elementary View of the_ UNDULATORY _Theory of_ LIGHT. _By_ Mr.
FRESNEL.
[Continued from the last Number.]
I shall not undertake to explain here in detail the reasons and the
calculations which lead to the general formulas that I have employed
to determine the position of the fringes and the intensity of the
inflected rays: but I think it right to give at least a distinct idea
of the principles on which this theory rests, and particularly of the
principle of _interference_, which explains the mutual action of the
rays of light on each other. The name of interference was given by
Dr. YOUNG to the law which he discovered, and of which he has made so
many ingenious applications.
This singular phenomenon, so difficult to be satisfactorily
explained in the system of emanation, is on the contrary so natural
a consequence of the theory of undulation, that it might have been
predicted from a general consideration of the principles of that
theory. Every body must have observed, in throwing stones into a
pond, that, when two groups of waves cross each other on its surface,
there are points at which the water remains immoveable, when the
two systems are nearly of the same magnitude, while there are
other places in which the force of the waves is augmented by their
concurrence. The reason of this is easily understood. The undulatory
motion of the surface of the water consists of vertical motions,
which alternately raise and depress the particles of the fluid. Now,
in consequence of the intersection of the waves, it happens, that
at certain points of their meeting, one of the two waves has an
ascending motion belonging to it, while the other tends at the same
instant to depress the surface of the liquid: consequently, when
the two opposite impulses are equal, it can neither be actuated by
one nor the other, but must remain at rest. On the contrary, at the
points in which the motions agree in their direction, and conspire
with each other, the liquid, urged in the same direction [p114] by
each of the forces, is raised or depressed with a velocity equal
to the sum of the effects of the two separate impulses, or to the
double of either of them taken singly, since they are now supposed
to be equal. Between these points of perfect agreement and complete
opposition, which exhibit, one the total absence of motion, the other
the maximum of oscillation, there are an infinity of intermediate
points, at which the alternate motion takes place with more or less
of energy, accordingly as they approach more or less to the places of
perfect agreement, or of complete opposition of the two systems of
motion which are thus combined, or superinduced on each other.
The waves which are propagated in the interior of an elastic fluid,
though very different in their nature from those of a liquid like
water, produce mechanical effects by their interference, which are
exactly of the same kind, since they consist in alternate oscillatory
motions of the particles of the fluid. In fact, it is sufficient that
these motions should be oscillatory, that is, that the particles
should be carried by them alternately in opposite directions, in
order that the effects of one series of waves may be destroyed by
those of another series of equal intensity; for, provided that the
difference of the route of the two groups of waves [derived from the
same origin] be such, that for each point of the fluid the motions
in one direction, belonging to the first series, correspond to the
motions, belonging to the second, in the opposite direction, they
must perfectly neutralise each other, if their intensity is equal:
and the particles of the fluid must remain in repose. This result
will always hold good, whatever may happen to be the direction of the
oscillatory motion, with regard to that in which the undulations are
propagated; provided that the direction of the oscillatory motion be
the same in the two series to be combined. In the waves which are
formed on the surface of a liquid, for example, the direction of the
oscillation is [principally] vertical, while the waves are propagated
horizontally, and consequently in a direction perpendicular to the
former; in the undulations of sound, on the contrary, the oscillatory
motion is parallel to the direction of the propagation of the sound,
[or rather is [p115] identical with it]; and these undulations, as
well as the waves of water, are subject to the laws of interference.
The undulations formed in the interior of a fluid have here been
mentioned in a general manner: in order to form a distinct idea of
this mode of propagation, it must be remarked, that when the fluid
has the same density and the same elasticity in every direction,
the agitation produced in any point must be propagated on all sides
with the same velocity: for this velocity of propagation, which
must not be confounded with the absolute velocity of the particles,
depends only on the density and elasticity of the fluid. It follows
thence that all the points, agitated at the same instant in a
similar manner, must be found in a spherical surface, having for its
centre the point which is the origin of the agitation: so that these
undulations are spherical, while the waves, which are seen on the
surface of a liquid, are simply circular.
We give the name of _rays_ to the right lines drawn from the centre
of agitation to the different points of this spherical surface; and
these rays are the directions in which the motion is propagated.
This is the meaning of the term _sonorous rays_ in acustics, and of
_luminous rays_ or _rays of light_ in the system which attributes the
phenomena of light to the vibrations of a universal fluid, to which
the name of ether has been given.
The nature of the different elementary motions, of which each
wave is composed, depends on the nature of the different motions
which constitute the primitive agitation. The simplest hypothesis
that can be entertained concerning the formation of the luminous
undulations, is, that the small oscillations of the particles of the
bodies, which produce them, are analogous to those of a pendulum
removed but little from its point of rest; for we must conceive the
particles of bodies, not as immoveably fixed in the positions which
they occupy, but as suspended by forces which form an equilibrium
in all directions. Now, whatever the nature of such forces may
be, as long as the displacement of the particles is but small in
proportion to the extent of their sphere of action, the accelerating
force which tends to restore them to their natural position, and
which thus causes them to oscillate on each side of it, may always,
without sensible error, be considered as proportional [p116] to the
magnitude of that displacement: so that the law of their motion must
be the same as that of the motion of the pendulum, and of all small
oscillations in general. This hypothesis, which is suggested by the
analogy with other natural phenomena, and which is the simplest that
can be formed respecting the vibrations of the luminous particles,
may be considered as experimentally confirmed by the observation,
that the optical properties of light are all independent of any
circumstances which cause the greatest difference in the intensity of
the vibrations: so that the law of their motion must be presumed to
be the same for the greatest as for the smallest.