686 
DE. C. W. SIEMENS ON DETERMINING THE DEPTH OP THE SEA 
care peculiar to the observer ; but no such cause could possibly have operated regarding 
the observations of the instrument recorded in the series of observations given in the 
second Table, when the vessel passed through seas Avhich had not been before sounded, 
but which were sounded after each observation of the instrument had been made. 
In this Table columns 1 and 2 contain the dates and hours observations were made ; 
3 and 4, the latitude and longitude of the locality when ascertained; 
5, the indications of the thermometer ; 
6, the indications of the barometer; 
7, the indications of the bathometer ; 
8, the corrections for variations in temperature and atmospheric density ; 
9, the readings of the bathometer so corrected. 
10, the soundings taken. 
11, the difference of these and the bathometer indications. 
The soundings were made by means of Sir William Thomson’s steel-wire sounding- 
apparatus, by which admirable improvement over the old sounding-line it is now 
possible to take soundings exceeding 2000 fathoms in an hour, when 5 or 6 hours 
Avere formerly required, and by the application of mechanical power to recover the 
steel wire itself in from 15 to 20 minutes when a detaching-weight is employed. 
The reading of the bathometer was in each case reported to Captain Teot, of the 
steam-ship ‘ Faraday,’ before the sounding-line had reached the bottom ; and the fair 
accordance between the results obtained by sounding and those given by the instru- 
ment furnishes ample proof of the reliable nature of the bathometer indications. The 
series of observations was unfortunately interrupted during the homeward voyage by a 
heavy gale, whereby the instrument was exposed to splashes of sea-water from the 
deck ; it had to be taken down, and was only remounted when the vessel had arrived 
at Victoria Docks. It will be observed that the readings taken in the Victoria Docks, 
before and after the voyage, agree, after allowing for difference of temperature and 
atmospheric density, within 5 divisions on the scale of the instrument, representing 
5 fathoms of depth, an accordance which must be considered highly satisfactory. 
Influence of Elevation above the Eartlis surface. — The bathometer is applicable also 
to the measurement of height, for which purpose it possesses the advantage over the 
aneroid barometer that its indications are not affected by changes of atmospheric 
pressure, excepting the small correction for change of atmospheric density before 
referred to, and which could be avoided in excluding the atmosphere from the extre- 
mities of the mercury column. 
The total attraction of the earth varies in the inverse ratio of the square of the 
distance from the centre of the earth ; and the ratio of the attraction on the surface of 
the earth, and at a height h above the surface (supposing the earth to be a sphere), will 
be expressed by 
w (R + Aj 2 
w’~ R 2 ’ 
