In considering the work done by the expedition it is very necessary to
bear in mind the character of the instrumental outfit, if any, which
they might have possessed, and the state of the science of navigation
at the time.
When Bering and his two cartographers left St. Petersburg in February,
1725, the astronomical instrument in use by navigators was the Davis
quadrant or "backstaff," in which the sun's altitude was measured by
sighting without a telescope or tube on the shadow cast by the sun from
one projection of the instrument upon another, the observer's back of
course, being turned to the luminary. The only alternative to this was
the still older astrolabe with which the observer had to look along the
two lines of his angle at the same time, and which also depended upon
sights or spurs attached to a frame. The reflecting quadrant of Hadley
was not invented until 1731 and telescopes were not used on the
instruments of navigation until somewhat later. There were no
chronometers or reliable watches or clocks for use in dividing
intervals of time. Even after the Hadley quadrant came into use, time
was noted by a pendulum vibrating seconds, which could not be used on
ship-board.
A futile attempt had been made by means of tables of variation of the
compass to determine the longitude by comparison with observed
variation in the field. Results by this method approached the truth
accidentally, if at all. Lunar observations were the only means of
getting an approximation to the longitude except the occultations of
Jupiter's satellites, both methods being impracticable on board ship,
with the instruments then employed.
In 1731 the astronomer Halley proved[2] that at that date it was still
impossible to find the longitude correctly by the moon, the lunar
tables being so inaccurate that an error of several hundred miles was
quite possible and an accurate determination would depend upon the
respective errors of instrument, observation and the lunar tables
happening to balance one another. Halley ventured to express the hope
that the tables may be so amended that an error may scarce ever exceed
three minutes, which would correspond to a degree and a half of
longitude, amounting at the equator to a distance of a little less than
one hundred miles. Messerschmidt, who preceded Bering as an explorer of
Eastern Siberia, was according to Middendorf (Sib. Reise, iv. 1, p. 56)
thirty-two degrees out in his determination of the longitude, and the
eastward extent of Asia in this region was underrated by that amount or
thereabouts, on many maps.
[Footnote 2: Phil. Trans. 1731, No. 421.]
One other means of approximating to the meridian remained, in the
observation of eclipses. This from the comparative rarity of these
occurrences in the case of the sun and moon, could with the imperfect
instruments of those days be available but seldom. Owing to the
difficulty of determining the exact time of the first and last contacts
the longitudes computed by these observations were liable to quite as
great inaccuracy as those computed from the lunar tables. Still an
ordinary spyglass would enable an observer to note the time within a
minute or two, and, if he was possessed of the local time, a simple
comparison with the observed time of the eclipse in some locality where
the longitude was known would give a fairly good determination,
considering the instruments and methods of those days. Of the four
eclipses of the moon occurring in 1728-9 two might have been observed
without difficulty by Bering, one would have been invisible to him, and
one might barely have been noted, but in all probability was not
observed by him. In none of the published reports of the expedition is
any mention made by Bering or his officers of the occurrence or
observation of an eclipse, which seems very singular if by such an
observation he was enabled to correct an error of 30° in the longitude
of northeastern Siberia. However, Middendorf states (Sib. Reise, iv. 1,
p. 56) that "Bering and his lieutenant in the years 1728 and 1729
observed in Kamchatka[3] two eclipses of the moon," by which they
corrected the longitude. He gives no authority for this statement.
[Footnote 3: It is possible that an eclipse observed at Ilimsk in
Middle Siberia by Chirikoff is thus erroneously referred to.]
Euler, who had access to the archives of the Admiralty College, while
engaged on a Geography of Russia, mentions (Philos. Trans., No. 482, p.
421) that he was informed that Bering observed an eclipse "at
Kamchatka." This letter of Euler's is copied by Campbell in Harris'
Voyages (vol. II, Book III, p. 1024) and the expression "at Kamchatka"
has led to the statement that these observations were made at the fort
or village of Lower Kamchatka. This is an error since Bering gives no
longitude for the fort in his table of geographical positions. It must
be remembered that the name Kamchatka at that period was applied not
merely to the peninsula as at present, but also to the whole region of
northeastern Siberia, the governor of Kamchatka being located at
Okhotsk. So to come within the probable meaning of the phrases used by
Middendorf and Euler it is only necessary to suppose that the
observations were made somewhere in that region. Lauridsen (Danish
edition, note 34, p. 186) refers to a paper of Struve (Bull.
phys.-math. Acad. St. Petersb., I, 1842, p. 290) containing a table of
geographical positions in Russia, in connection with these alleged
observations of Bering. An examination of Struve's paper does not bear
out the implication of Lauridsen's reference, as Struve not only makes
no mention whatever of Bering's observations there but specifically
states that the first observations of precision made in this part of
Siberia were those of Krassilnikoff who accompanied Bering's second
expedition in 1741. It would seem extraordinary that a determination so
important for geography as that of Bering and his companion should be
unknown to so distinguished an astronomer as Struve who must have had
access to all the archives of the early explorations by Russia. But it
may be perhaps accounted for by the facts that Bering's observations
were necessarily of a very rough and primitive character--as it is
certain he had no instruments of precision; and that, for that reason,
they were not received with entire confidence; so that Struve may have
considered them insufficiently exact to be included with those of
Krassilnikoff and others made with more modern appliances.
From the note in regard to the eclipses which is kindly contributed by
Mr. Marcus Baker and from the other circumstances, it is evident that
if Bering and his party made the observations alluded to, the eclipses
noted were the partial eclipse of Feb. 25 (local calendar), 1728, of
which he might have observed the last contact, or the total eclipse of
Feb. 14, 1729, of which he might have observed the first contact and
the totality. At the time of the last eclipse he was at Lower Kamchatka
post, and as, in the list of positions handed in with his Report in
1730, no longitude is entered for this locality, it would seem that
choice is reduced to the first of the two mentioned; which occurred
when Bering was either at Bolsheretsk or on his way from that place to
Lower Kamchatka, which he reached about a month later. Campbell's table
of positions is credited by him to the year 1728, but my own opinion is
that it was really derived (with various errors, interpolations, etc.)
from Bering's table of 1730.
The ordinary method of getting the longitude of a place, and that upon
which Bering originally depended, as his itinerary table shows, was by
a continuous record of the distances and directions traveled from a
point of known longitude. This record would afford the data from which
the distance on a mean parallel, by means of a traverse table, could be
computed. Laborious, imperfect, and slow as it was, it was the only
sure reliance of the traveler in those days. Whether Bering observed an
eclipse or not, it is certain that his original dependence was upon his
itinerary, that his report was based upon that and that this part of
his work was done as well as the nature of the method would permit. His
silence about the eclipse may be due to the fact that he depended not
upon astronomical but upon pedometric observations, to which the
eclipse may have afforded some corrections. At any rate the pedometric
determination of the distance between Tobolsk and Okhotsk or the
peninsula of Kamchatka was in itself a tremendous undertaking.
I find by a rough calculation from Bering's data that the longitude
resulting from his itinerary from Tobolsk to Okhotsk is 77° 36' E. The
distance in a straight line is about 2,390 miles, but by the route
Bering traveled the distance is a little more than 3,746 miles. The
longitude in Bering's List of Positions is 76° 07', which differs from
the pedometric measurement by 1° 29' (or about 45 miles). On Bering's
map, Okhotsk is located in longitude 74° 30' E. of Tobolsk, while the
most modern observations for Okhotsk put it in 142° 40' E. of Greenwich
or 75° 40' E. of Tobolsk. So that Bering's pedometric measurement was
nearly 60 miles in excess; his revised table (as corrected by the
eclipse?) 27 miles in excess; and his map about 30 miles in error in
the opposite direction. These discrepancies show the inexactness of the
methods then in vogue and also that the pedometric method was not very
much worse than the others in its results. Although there are several
typographic or other errors in his table of itinerary which render
exact comparisons impossible, it may be said that the error of the
pedometric method, including the passage by sea from Okhotsk to
Kamchatka, averages about two degrees or sixty geographical miles. In
the cases of Okhotsk and Bolsheretsk the error is one of excess; in the
case of the cape at the mouth of the Kamchatka river and of the turning
point of the expedition north of Bering Strait, the result is too small
by about the same amount.
That his chart and his revised list of positions should differ as they
do, is quite as likely the result of the careless way in which the
minutiæ of such work were generally regarded at that day, as to any
difference of date, or of intentional modification.
To conclude our review of the instrumental means and methods then in
use, it may be said that the compasses in use at that day were
comparatively roughly made and more or less inaccurate. The variation
was determined in a given latitude by the azimuth of the Polestar or
the sun at setting observed by means of sights attached to the rim of
the compass, which was a method accurate enough for the general
purposes of navigation. The distance run was measured on shipboard by
the log which was in about the same form and perfection as at present,
being a very ancient invention.
The survey of a general coast-line was made by compass bearings on
prominent points, repeated from successive stations, the distances of
the ship's course being determined by the log and the courses by
compass, with corrections for current and the variation. The lines thus
obtained were checked by latitude observations made with Davis'
backstaff when the weather permitted.
Apart from any of the methods mentioned it seems to have been
overlooked that Bering might have corrected the longitudes of the N.E.
Siberian coast by the ordinary dead reckoning kept on board his vessel,
provided he started by adopting the longitude for the southern part of
Kamchatka peninsula which was in common use on many of the charts of
his day. Though it is true that the maps of that part of Siberia north
and northeast from the Okhotsk sea were many degrees in error in the
longitude, this observation does not hold good in regard to the
southern end of Kamchatka. The work of the Jesuit fathers in China had
already determined fairly well the position of China and Korea, while
rude outlines of the northern islands of Japan, Sakhalin, the Kuriles
and the south end of Kamchatka, were added to these on maps of Asia.
The outlines are often very incorrect but it is quite evident what is
intended. In nearly all early maps of this region which I have been
able to consult, as for instance those of N. de Witt, I have found the
south end of Kamchatka in approximately correct longitude. For
instance, in the Novissimae Ephemerides of Manfredio, published at Bonn
the same year that Bering left St. Petersburg, and which might well
have been sent to him before he sailed, we find two charts of the paths
of solar eclipses (Plates ii and iii). On these charts the meridian of
180° from Ferro passes across what is unmistakably the south end of
Kamchatka, though northeastern Siberia remains a blank. This would be a
sufficient starting point and is quite as correct as Bering's
determinations; in fact is within a few miles of the modern longitudes
for the same part of the peninsula. Dead reckoning along the shores of
the peninsula, corrected by latitude observations, would have done all
that was necessary to correct the meridian without observing any lunar
eclipse, provided the surveyor started with such an assumption as
Manfredio's or De Witt's charts supply.