34 



Mr. E. J. Stone on the Velocity of Sound. [Nov. 23, 



since n is very large, we may disregard — - — h^-^ ^ Cm ^ e ^us nave 



E=S?i— log e ?z, or $?z = log e w+E ; but log e «=log e 10x1 followed by 

 100 ciphers, therefore 



S ;i =2'30258 50929 94045 68401 79914 54684 36420 76011 01488 62877 



29760 33327 90096 75726 09677 35248 02359 97 2 °5 °8959 82983 



99889 35053 24395 34694 06073 44733 2 3°49 86088 22209 63091 



14157 00596 30696 81232 73586 10266 98852 09395 27703 06845 



6 3633 



August 28th, 1871. 



III. "An Experimental Determination of the Velocity of Sound." 

 By E. J. Stone, M.A., F.R.S., Astronomer Royal at the Cape 

 of Good Hope. Received August 21, 18.71. 



(Abstract.) . . - . 



A galvanic current passes from the batteries at the Royal Observatory, 

 Cape Town, at 1 o'clock, and discharges a gun at the Castle, and through 

 relays drops a time-ball at Port Elizabeth. It appeared to the author that 

 a valuable determination of the velocity of sound might be obtained by 

 measuring upon the chronograph of the Observatory the interval between 

 the time of the sound reaching some point near the gun and that of its arrival 

 at the Observatory. As there is only a single wire between the Observatory 

 and Cape Town, some little difficulty was experienced in making the neces- 

 sary arrangements, without any interference with the 1 o'clock current to 

 Port Elizabeth ; but thi's difficulty was overcome by a plan which the author 

 describes, and which was brought into successful operation on Feb. 27, 

 1871. The experiments could not have been carried out, on account of 

 the encroachment they would have made on the time of the Observatory 

 staff, had it not been for the assistance of J. Den, Esq., the acting manager 

 of the Cape Telegraph Company, to whom the author is indebted for the 

 preparation of a good earth-connexion near the gun, for permission to 

 Mr. Kirby, a gentleman attached to the telegraph office, to assist in the 

 experiments, and for a general superintendence of the arrangements" at 

 Cape Town. .-. 



The observed times of hearing the sound were recorded on the 

 chronograph by two observers, situated one (Mr. Kirby) at a distance of 

 641 feet from the gun, the other (Mr. Mann) at the Observatory, at a 

 distance of 15,449 feet from the gun. The former distance was sufficient 

 to allow the connexion of the main wire to be broken at the telegraph 

 office after the gun had been fired, but before the sound reached the first 

 observer. . .. 



As there were no reciprocal signals, a correction was made by calculation 

 for the effect of the wind, its velocity being measured by a set of Robin- 



