162 Prof. Faraday on associated cases, in Electric Induction, 



paper showing the results. 1 was unable to equalize the deflec- 

 tions of a galvanometer by currents of intensity with small plates 

 as compared with currents from a few large plates, for no size 

 of plate would make up for the deficiency in intensity. I allude 

 to the form of experiment suggested by Melloni ; — but I believe 

 they will be of interest to him. 



" The experiments were made through 768 miles of gutta 

 percha wire, viz. from London to Manchester and back again 

 twice, with our ordinary sulphate of copper batteries, plates 

 3 inches square, and with intensities varying from 31 cells to 

 sixteen times 31 cells, or 500 cells. 



" In the accompanying strips the upper line indicates the 

 time during which the current was sent, being made by a local 

 arrangement. 



"The second line (of dots) indicates time by seconds, being 

 made by a pendulum vibrating seconds, and striking a light 

 spring at the centre of its arc of vibration. 



"The third line indicates the time at which the current 

 appeared at (what we may call) the distant end of the line, 768 

 miles off. 



" The fourth line merely shows the residual discharge from 

 the near end of the wire, which was allowed to communicate with 

 the earth as soon as the batteries were disconnected ; this has no 

 reference to the subject of our inquiries. 



" It will be seen by the third line, that about two-thirds of a 

 second elapsed in every case before the current became apparent 

 at the distance of 768 miles, indicating a velocity of about 1000 

 miles a second ; but the most interesting part appears to be, that 

 this velocity is sensibly uniform for all intensities from 31 cells 

 to 500." 



Melloni has then given a copy of the records made when 31 pair 

 and 500 pair of plates were employed ; unfortunately the copy 

 is inaccurate, since it makes the fourth line commence as to time 

 at the termination of the third, whereas it ought to correspond 

 with the termination of the first ; also the third line on each does 

 not thin off as those upon the record do. The following is a copy 

 from other slips obtained at the same time from the Bain's print- 

 ing apparatus. Experiments with 62, 125, and 250 cells, gave 

 like results with those of 31 and 500 cells. 



After certain observations, which are mainly upon the manner 



