Review of Bering s First Hxpedition, 1725-30. 118 
indebted for numerous favors and courteous assistance, and to 
all of these gentlemen I desire to express my thanks. 
In conclusion I desire to state that I am well aware this paper 
cannot be regarded as a finality, but as a contribution to the geo- 
graphical history of North America it will not be without its 
value, while the fact that I have myself spent parts of three 
summers in scientific exploration of the coast visited by Bering 
and first charted by him, has greatly helped me in my discussion 
of minor details of his work. 
INSTRUMENTS AND MeEruops. 
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 naviga- 
tors 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 astro- 
labe 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 varia- 
tion 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* that at that date it was 
still impossible to find the longitude correctly by the moon, the 
* Phil. Trans. 1781, No. 421, 
‘ 
