1891.] the Discharge of Ley den Jars. 29 



riments do make clear, viz., that the velocity of a pulse along an 

 isolated thin copper wire is practically identical with the speed of 

 light ; in accordance with the theory based on Maxwell, and previously 

 mentioned. Hertz at one time stated, as the result of some of his 

 experiments, that there was considerable discrepancy between the 

 speed of waves along wires and of waves in free space ; and, though 

 my own experiments were (to me at least) conclusive in the opposite 

 direction, yet as they had not been published in detail, they could not 

 be properly taken into account. The supposed discrepancy, however, 

 had the good effect of leading Professor J. J. Thomson to make 

 several interesting experiments. 



QUANTITATIVE RECOIL KICK EXPERIMENTS (May, 1888). 

 Description of Wires used. 



31. In order to make real measurements of wave-length, a circuit 

 was carefully prepared, consisting of two copper wires (about No. 17 

 B.W.G.), 15 cm. diameter, stretched parallel to one another, half a 

 metre apart, by silk suspenders. 



They lay parallel to the theatre table, i.e., north and south; but 

 the room was not big enough for them to be wholly straight, so after 

 travelling the length of the table horizontally they were taken 

 a few feet vertically up, then back over head, and down again to the 

 spark micrometer, according to the plan of fig. 16, nowhere being 

 taken near any wall or other surface. Their total lengths were 



1526 + 28-5 + 16 = 1570-5 cm. 

 1529 + 36-5 + 16 = 1581'5 



so each may be taken as 15f metres long, and the wave length corre- 

 sponding to their fundamental oscillation period as 31 J metres, corre- 

 sponding to about 10,000,000 vibrations per second. 



When used alone, these are spoken of as " the shorter leads," be- 

 cause it was very soon necessary to supplement them by a similar pair 

 of No. 17 copper wires half a metre apart, suspended similarly, but in 

 an east and west direction, and used as extensions. When joined up 

 in series with the former pair of wires the whole is spoken of as " the 

 longer leads." The additional portions measured 2263 and 2247 cm. 

 respectively. Hence the entire length of each of the longer leads 

 may be taken as 38'2 metres, and the wave-length correspond- 

 ing to their recoil as 76^ metres, or say, 4,000,000 vibrations per 

 second. 



The total resistance of the "shorter leads" was 0'78 ohm, and of 

 the " longer leads," 1'95 ohms. 



The static capacity of the longer leads I estimate, by the formula 



