374 THE SCIENTIFIC PAPERS OF 



several readings (the first observed Westminster indications being 

 taken as the standard), the above indications may be reduced to 

 the following : 



Bathometer. 

 Before leaving Westminster .... 431 



At Brighton 452 



On return to Westminster .... 439'25 



Taking the mean of the Westminster readings, there would be 

 a difference on the scale of 17 divisions, equivalent to a diminu- 

 tion in attraction of '0000046, whereas calculation gives a 

 difference of '000066. 



I have not succeeded in finding a satisfactory explanation of 

 this apparent anomaly, which can hardly be attributable to defects 

 of the instrument or to errors in observation, because on taking 

 the instrument on board the steamship " Faraday " from the 

 Thames down the Channel, the variations observed (as recorded in 

 the Table, p. 375) accord very fairly with the increasing depth of 

 water, but give no evidence of the great variations in total gravita- 

 tion due to differences in latitude. In order to test the influence 

 of latitude further, I caused the instrument to be taken to Scar- 

 borough, which is 207 miles north of Westminster ; and the 

 observations there taken confirmed generally those of Brighton, 

 in showing insufficient variation, although their absolute value 

 was rendered unreliable by an accidental disturbance of the instru- 

 ment in transit. 



It must be borne in mind that both Brighton and Scarborough 

 are on the sea-shore, and that Westminster is upon an inland 

 estuary, which circumstance would exercise an influence in the 

 direction of equalizing the total gravitation at Brighton and 

 Westminster. 



ACTUAL TRIAL OP THE INSTRUMENT ON BOARD SHIP. The 

 foregoing may suffice to show what are the disturbing influences 

 to be met with in the use of the instrument which forms the 

 subject of this paper ; but it was important to ascertain what 

 would be the actual indications of the instrument in taking it on 

 board ship over seas of varying and known depth, in order to 

 compare the indications of the instrument with those of the 

 sounding-line. For this purpose two instruments, the smaller of 



