1876.] determining the Depth of the Sea. 319 



the extremities of the column. The only necessary correction is that for 

 latitude, which it is asserted in the paper must be less variable on the sea 

 than on land, owing to the absence of masses elevated above the surface, 

 and owing to the comparative greater distance of the irregular solid con- 

 stituents of the earth and the very uniform density of sea-water. 



The paper contains tables of the result of actual observations of the 

 instrument in twice crossing the Atlantic on board the steamship ' Fara- 

 day,' while she was engaged upon laying submarine cables. The readings 

 of the instrument were checked by actual soundings taken by means of 

 Sir "William Thomson's steel-wire sounding-apparatus ; and the compa- 

 rable results agree in all cases as closely as could have been expected, 

 considering that the sounding-line gives the depth immediately below the 

 vessel, whereas the bathometer gives the mean depth taken over a certain 

 area, depending for extent upon the depth itself ; it is also shown that 

 upon an even slope the two instruments may be expected to agree in their 

 indications. 



It is thought that the bathometer may render useful service to the 

 mariner in warning him of changes of depth long before reaching dan- 

 gerous ground. An example is recorded where the position of the end of 

 a submarine cable in deep water was found simply from a knowledge of 

 the depth in which the end had been lost ; and it is shown how the posi- 

 tion of a vessel, when no astronomical observations can be taken, may be 

 ascertained by the aid of a bathometer, provided the contour-lines of equal 

 depths of oceanic basins were accurately laid down. 



The instrument is applicable also for measuring elevations above sea- 

 level ; and it is shown that for height the total attraction of the earth 

 varies in the ratio of 



h : jB, 



and that therefore approximately the fathom-readings at sea may be taken 

 for yard -readings in measuring height ; but that in this last application 

 allowance will have to be made, in addition to corrections for latitude, for 

 the local attraction of the elevated land itself, varying with its breadth, 

 and rendering the indications of the instrument for height less reliable 

 than for depth of sea. 



Addendum. — On an Attraction-meter. Received February 23, 



1876. 



At the reading of the foregoing paper, the author exhibited an 

 instrument for measuring horizontal attractions, which, at the same 

 time, illustrates the action of the bathometer. This instrument con- 

 sists of a horizontal tube of wrought iron 400 millims. long, termi- 

 nating at each end in a horizontal transverse tube of cast iron of 60 

 millims. diameter and 300 millims. long. The first-named horizontal 

 tube is partially closed at its ends, and communicates with the transverse 



