DEEP-SEA EXPLORATION. 
335 
One can .judge of the (luantity drawn o(f only by the sound and such circuni- 
stanees. A note, however, is always kei)t of the weights of tlie stock llask, giving 
not only liow much has been withdrawn, but its ])resent contents as well. Between 
4 and 5 jtounds of anunonia are sutlicient to lower the temperature to —05° and work 
at various intermediate temperatures for several hours. The temperature can be 
readily lowered to any point down to — 20° F., simply using the rublier tube and 
water vessel. At this point, however, the escape of the ammonia gas is slow, owing 
to its diminished pressure. The pump shown at F is tlien brought into requisition. 
The diameter of the barrel is nearly 3 inches and the construction is somewhat 
peculiar, there being but one valve. Connection with the flask A is made at the top 
of the pump, the communication with the inside being through the small holes near 
tlie top of the cylinder. The piston when in its highest position is above these holes. 
At the bottom of the cylinder is a large, flat valve, closing upward with gentle 
liressure. From the valve way the passages to the outside are seen in the side view 
of this portion of the pump. The valve itself is pierced with a small hole of only 
about oue-sixteentli inch diameter, and the whole punq) is securely fastened inside a 
bucket or similar vessel nearly filled Avith Avater, Avhich makes its way into the immp 
tlirough the small hole in the valve; in some cases of low inside pressure quite a 
fountaindike jet of Avater is formed. With the piston in its highest position the 
ammonia has free communication to the pump cylinder and is rapidly absorbed by 
the Avater which is readily renewed by emptying the cylinder Avith a stroke of the 
l)iston. The absorption of the ammonia by the Avater is very vigorous generally, 
and the number of strokes of the pump necessary to dispose of a comparatively large 
volume of gas is correspondingly small. 
The pump is remai'kably effective, though Avhen not in action the piston must 
be secured in a lowereel position in order to prevent the rise of heated Avater into the 
tube and possibly the tlask A, though the valve of the latter is generally kept closed 
when the gas is not lieing draAvn off. During the escape of the gas the tlask and its 
contents are always noticeably colder than the alcohol, so that it is easy to secure 
very nearly a stationary temperature of the latter for several minutes, shortly after 
the valve is closed. 
Except as otherwise specially mentioned all measurements of the differences in 
level of the mercurial columns Avere made Avith a most excellent and substantial 
cathetometer made some years since by the Societc Genevois. The vertical bar is a 
cylinder supported on sharp cones at both top and bottom. The two telescopes are 
each fitted Avith excellent micrometer eyepieces. Only one of these Avas used, and its 
micrometer screw Avas examined for errors, Avhich Avere found so small as to be quite 
unimportant, and no correction for this Avas necessary. Except in the very first 
work the distance of tlie manometer tubes from the objective Avas 359 mm., and the 
micrometer reticule Avas 349 mm. from the objective. The image, therefore, is about 
the same size as the object. 
Many determinations of the value of one division of the micrometer Avere made 
during the progress of the Avork, Avith only very slightly different results. One 
division corresponded almost exactly to 0.005 nun., and this could be subdivided to 
tenths by estimation. 
The value of one division of the telescope level Avas nearly three seconds. The 
level was at all times carefully watched and sometimes recorded, but corrections for 
