of Wires of different Qualities and Dimensions. 7 



The lengths of the several parts were P G = \5± feet. 



Gc= U£ 

 37 \ turns on frame E =. 375 

 ba = 28 



37| turns on F ... =375 



DH = 144 



NH = 15£ 



Total = 838 feet. 



The three compasses on which the observations were made 

 were situated as shown at A, C, D ; the standard compass for 

 measuring the power of the battery was placed at A, and its 

 deflection taken prior to each experiment, as described in the 

 former case, and two separate observations were made on each 

 length of wire by three observers, one at each compass *. 

 These observations and those on the standard compass being 

 made, the battery was raised out of the acid, and the wire short- 

 ened 40 feet by unwinding two turns from each frame: it was 

 then again lowered, and similar observations repeated, and 

 so on, till the length had been reduced from 838 feet to 98 feet. 

 The compasses and wire were continued at the same distance 

 at each station, till the wire had been shortened to 398 ; its 

 action was then so strong that I was enabled after every ob- 

 servation at the usual distance, to obtain another double ob- 

 servation with the compass at ]i inch distance; so that from 

 398 feet to 98 feet I obtained two distinct series, answering 

 to two different distances. The comparative results were very 

 nearly the same in both, but for the present comparison I shall 

 only use the longer series, and state the mean of every two 

 corresponding observations. Each individual observation may 

 be seen in the work already quoted. 



These mean results and comparisons are given in the fol- 

 lowing table. The 1st column contains the length of the con- 

 ductor; the 2nd, the deflection of the standard compass; the 

 3rd, the mean deflection of the three other compasses; the 

 4th, these deflections reduced to a constant standard deflec- 

 tion of 21°; the 5th, the computed deflections assuming the 

 law to be inversely as the square root of the length ; the 6th, 

 the errors arising from this assumption; the 7th, the com- 

 puted deflections, assuming the law to be inversely as the 

 length ; and the 8th, the errors arising from that assumption. 



* It is proper to observe, that at the time I made these experiments, 

 June 1824, I had attending me for instruction relative to my correcting 

 plate several of the junior civil officers of the Dockyards, formerly stu- 

 dents in the Royal Naval College, Portsmouth, to whose assistance I was 

 much indebted not only in the experiments, but in all the previous ar- 

 rangements. 



