THE BATHOMETER. 133 



have also taken the instrument up a certain height to the 

 clock-tower of Westminster for instance and have ob- 

 served an influence which was nearly equal to what calcu- 

 lation implied, although in taking such an instrument up 

 the clock-tower it is impossible to avoid some disturbing 

 influences which render the result of a few observations 

 less reliable than might be wished. 



I will now refer to the results of actual observations 

 taken several times across from this country to America, 

 on board the steam-ship Faraday. The instrument was 

 suspended near midships, and observed from time to time 

 while the sounding-line was let down to obtain the correspond- 

 ing actual measurement of the depth. The results by the 

 bathometer and by Sir William Thomson's sounding-wire 

 are placed in parallel columns, and the differences are not 

 great. There is enough to show that the instrument gives 

 indications which in all cases approach very nearly to the 

 actual results of measurement. We find in all these cases 

 that the instrument and the sounding-line agreed within 

 something like 5 per cent., and I thought that a very 

 satisfactory result considering the instrument is a new one 

 and defective in many respects, and as we are all new in 

 the use of the instrument. There is also another set of 

 observations which have been sent me from Nova Scotia, 

 lately taken by my nephew Mr. Alexander Siemens, and 

 they show the same close agreement between the two modes 

 of measuring in smaller depths. I should here observe 

 that it would be impossible to obtain exactly similar results 

 in reading this instrument, and in measuring by means 

 of a sounding-line, because you really measure different 

 quantities. The sounding-line gives the depth immediately 

 below the ship, whereas this instrument gives the average 

 depth over a certain area. Now this average depth over a 

 certain area will coincide with the actual depth below the 

 instrument if the sea-bottom is on a general slope. The 

 greater attraction at the rise of the slope will be balanced 

 by the lesser attraction where it descends, but if the sea- 

 bottom is irregular if there are rocks projecting from the 

 bottom the sounding-line may accidentally come upon a rock 

 and give a small depth, or may accidentally fall beside the 

 rock and give a greater depth ; whereas this instrument 

 would give the same depth, whether it was exactly over the 



