682 
DR. C. W. SIEMENS ON DETERMINING THE DEPTH OF THE SEA 
to Professor Stokes’s explanation of the matter. The working zero of the bathometer 
may be taken as a maximum or island indication ; and the diminution due to the depth 
of water is therefore not influenced by the irregularities met with on solid land, in 
consequence of the matter raised above the natural surface of the sea. It has, however, 
been shown by Archdeacon Pratt and others that continents exercise an influence 
upon the level of the sea, that level being raised up towards the masses piled above the 
surface ; and such disturbance of the natural water-level must necessarily exercise an 
influence upon the readings of the instrument. But this influence would be percep- 
tible only in estuaries or upon the sea-shore of a mountainous continent, and may be 
neglected in dealing with the surface of the sea under all ordinary circumstances. 
The more important disturbing cause affecting the instrument under this head is that 
of the ellipsoidal form of the earth and the varying centrifugal tendency on its surface, 
to which reference has already been made. 
Effects of Latitude . — The determinations of the effect of latitude upon gravitation as 
made by Newton, Clairaut, M‘Laurin, and others have already been alluded to, and it 
is important that the influence of this disturbing cause upon the instrument should be 
accurately ascertained in order that allowance may be made for latitude in its ordinary 
use. In order to test separately the effect of latitude upon the instrument, its indi- 
cations were taken on the 8th of December at Westminster, lat. 51° 31' N., long. 0° 7' W ., 
and afterwards at Brighton, lat. 50° 50' N., long. 0° 10' W., which is nearly due south 
of Westminster 41 nautical miles. At Westminster the indications were 
Bathometer. 
2 turns 432 
431 
430 
Barometer. 
30-425 
30-425 
30-425 
Thermometer. 
° Fahr. 
43-4 
43-6 • 
43-4 
The instrument was then 
carefully packed and removed to Brighton, where it was again set up. The first 
