J, Lovering— Measuring the Velocity of Electricity. 213 



to traverse this short distance (amounting to only -rrshnTsrs of one 

 second) hecame distinctly measurable by the relative displace- 

 ment which it produced in the images of two sparks, formed in a 

 rapidly revolving mirror. Hence the hasty conclusion was 

 adopted that the velocity of electricity was 288,000 miles per 

 second. The immense discrepancy between this result and those 

 afterwards reached by experiments on land and ocean lines of tele- 

 graph could not be overlooked, and an explanation was sought in 

 the different tensions of friction and voltaic electricity. This ex- 

 planation was unsatisfactory because direct experiments on tele- 

 graph wires appeai-ed to indicate that the velocity of electricity 



was independent of the strength of the battery, 

 itself vanishes, or changes its character, when s 

 to the law that the transmission time of electricity is proportional 

 to the square of the distance. Wheatstone's experiment simply 

 proved that electricity will go through one-quarter of a mile of 

 wire at the rate of 288,000 miles per second, and that it would 

 pass over only 268 miles of similar wire in one second. Now this 

 is a much smaller velocity than is found by experiments on either 

 land or ocean lines of telegraph ; the reason being, probably, that 

 in the inferences from Wheatstone's experiment no account has 

 been taken of the intervals of air which separated the different 

 branches of the conducting ware. 



The theoretical law, already stated, viz. : that the transmission 

 time increases with the square of the velocity, has been verified 

 experimentally by Gaugain. He used two threads of cotton, each 

 of which was 1-65 meters in length. When tried separately, the 

 transmission time on each was eleven seconds. When they w^ere 

 placed end to end, so as to double the length, the time was forty- 

 four seconds. 



x\s Wheatstone's experiment on the velocity of electricity has 

 never been repeated, and as direct experiments upon telegraph 

 Imes are not numerous and are not likely to be rapidly multipled, 

 and have not been hitherto very harmonious in their results, some 

 other indirect method of conducting the investigation may be 

 found of scientific value. For this purpose, I have availed mj^self 

 of Lissajous' method of compounding the rectangular vibrations 

 of two tuning forks, and amplifying the resultant motion, by the 

 twice reflected beam of light, which afterwards enters a telescope. 



The tuning forks and telescope are permanently fixed to a base- 

 board, so as to preserve their adjustment. Each tuning fork is 

 provided with an electro-magnet, in order to maintain its vibra- 

 tion for a long time. The tuning forks, when vibrating independ- 

 ently, are nearly in unison, each making about 128 vibrations in 

 one second. When the electro-magnets are brought into action, 

 by a voltaic current circulating continuously through them and a 

 standard tuning fork, furnished with an electro-magnet and a 

 break-circuit attachment, the first two forks are forced into exact 

 unison with the standard, and, therefore, with each other. Under 

 these circumstances, the resultant orbit seen in the telescope is in- 



