676 
DE. C. W. SIEMENS ON DETEEMINING THE DEPTH OE THE SEA 
view to the establishment of a submarine cable : it proved successful to the extent that 
I was able to predict, approximately, the depth that would be found on the use of the 
sounding-line. The difficulty, however, of observing the instrument was great, owing 
to the excessive pumping-action, the consequence of the oscillations of the ship, as well 
as to the difficulty of obtaining perfect uniformity of temperature. The method of 
observation pursued was to take series of ten observations of alternate maxima and 
minima positions of the film, or boundary line between the liquids, of which the mean 
was taken to be its true position upon the instrument ; but occasionally oscillations of 
extraordinary amount occurred, tending to vitiate the value of even these means. The 
instrument was both bulky and delicate, and it was found impracticable at the time to 
provide the ship with a sufficient store of ice (to be used in maintaining the instru- 
ment at a uniform temperature) to last during a lengthy voyage. In consequence of 
these drawbacks, I relinquished for a time the idea of constructing a reliable bathometer. 
Present construction of Bathometer . — Last year the practical difficulties encountered 
in laying submarine cables in water the depth of which had not been accurately ascer- 
tained beforehand, revived in me the conviction that an accurate instrument would be 
of considerable value, not only to the cable-layer but to the navigator generally, when 
unable to determine his position astronomically. In the instrument about to be 
described, the mercury column is retained as the representative of the force of gravi- 
tation, but the balancing force is obtained through two spiral steel springs, which are 
so adjusted to the force of the mercury column that changes of temperature are entirely 
eliminated from the result. 
The instrument, which is represented on Plate 64, consists of a tube of steel, with 
cup-like extensions at the two extremities, which is suspended in a vertical position 
from a universal joint, at some little distance above the centre of gravity of the system, 
with a view of preventing pendulous action. 
The upper cup-like extension of the tube is closed with a lid, provided with a closed 
stopper, which is screwed down when the instrument is not in use, and released for the 
access of atmospheric pressure shortly before observations are about to be taken. The 
lower portion is closed by means of a thin diaphragm of corrugated plate of steel, 
similar to the corrugated plates used in the construction of aneroid barometers. The 
centre of the diaphragm rests upon a crosshead, to which two carefully tempered steel 
springs are attached, which pass upwards on opposite sides of the mercury column, and 
are held at their upper extremities by adjusting-screws in the sides of the upper cup. 
The neck of the vertical pipe where it opens out into the upper cup is nearly closed by 
means of a disk or stopper of steel, perforated by a hole of only -2 millim. diameter, 
the object being to reduce the pumping-action on board ship to a minimum. Before 
screwing-in this stopper the tube is filled with boiled mercury up to about the middle 
of the upper cup. 
Available Force . — The mercury column represents the potential of force resulting from 
the area of the lower cup, multiplied into the height of column and the density of mercury. 
