WITHOUT THE USE OF THE SOUNDING-LINE. 
691 
Received December 19, 1876. 
Since presenting my Paper on the Bathometer to the Royal Society in February last, I 
have continued my endeavours to produce an instrument in such a form as to be prac- 
tically independent of the disturbing influences to which reference is made in my paper, 
and of a construction so simplified as to render the instrument available for practical 
uses. 
It is my intention to present before long a supplementary paper to the Royal Society 
describing the improved instrument, and giving an account of the further trials which 
I have had the opportunity of making, for the purpose of verifying the indications of 
the instrument by actual sounding. 
The first set of observations was made by Mr. Alexander Siemens, on board the 
steam-ship £ Faraday,’ in American waters of a depth not exceeding 100 fathoms, when 
the readings were found to accord closely with the results of sounding. Besides this, 
several trials of the instrument have been made : one under my immediate superin- 
tendence in crossing lately from New York to Liverpool, on board the steam-ship 
4 Bothnia,’ Capt. M 4 Mickan (who rendered me every facility) ; another on board H.M. 
steam-ship 4 Fawn,’ between Southampton and Gibraltar ; while another has been 
made, at the instance of Dr. Higgs, with a modified form of apparatus, on board a 
sailing-ship in its passage from Southampton to Rio Janeiro. The results of the obser- 
vations on board the 4 Fawn ’ were unsatisfactory, owing to a mechanical defect in the 
apparatus, whereas the others confirmed generally the results given in my paper, 
confirming also the observation there referred to, that differences of latitude do not 
seem to exercise the full amount of effect upon the instrument which might be expected, 
in consequence of the combined influence of centrifugal force and ellipticity of the 
earth. 
Criticisms have appeared in several papers questioning the applicability of the 
bathometer for determining the depth of the sea, owing to the disturbance of the sea- 
level by continental attraction. This cause of disturbance had not escaped my attention 
in writing my paper*; and it should be borne in mind that the instrument cannot do 
more than indicate comparatively small variations in total terrestrial attraction, which 
the hydrographer or navigator using the bathometer will have to interpret according to 
the circumstances of the case. The zero-point of the instrument must vary no doubt 
with latitude, continental attraction, and also in consequence of special geological 
causes ; but it is important to observe that these causes are of a permanent character, 
and that if an ocean has been once surveyed with the aid of the bathometer, such 
special local conditions would become observed facts, and so far from hindering the 
* See page 682. 
