18250 Velocity of Sound. Stl 



in 10,000,000 parts, and one of the indexes gives .^ part of a 

 decimal second. This index or second hand remains quiet, 

 jyjiilst the watch work continues moving as long as a certain 

 nring is not pressed down with the finger; and on removing 

 'io finger, the index is reduced to rest in the identical moment, 

 hus the index being at 0, the spring is pressed down by the 

 observer at the very instant the light of the opposite station is 

 observed ; the index continues moving till the report of the shot 

 is heard, when the finger is withdrawn, and the index stopped 

 instantaneously. The number of turns and fractions of a turn 

 g.f the index shows the time elapsed between the fire and the 

 report. There was a conical or centrifugal clock on each sta- 

 tion ; besides these, each station was furnished with a good 

 barometer, carefully compared with a standard barometer of Mr. 

 Pollond, several good thermometers made by Messrs. Dollond 

 and Newman, besides a sufficientnumber of excellent telescopes 

 of DoUond's, and so placed on stands adapted for the object as 

 to bring the opposite station without trouble in the field of the 

 telescope. The moisture of the air was determined for the first 

 tii)me in such experiments by Mr. Daniell's hygrometer, one of 

 yi^hich was placed at each station. The direction of the wind 

 was determined by very good vanes contrived by the Artillery 

 ofiicers. At each station a twelve pounder and a six pounder 

 was planted, and the instruments were disposed in, or in the 

 vicinity of tents erected for the purpose. Professor Moll^ with 

 Lieutenants Renault and Dilg, was stationed at the KooUjesherg, 

 Dr. Van Beek, with Lieutenants Sommerton, Van Den Bylaardt 

 and Seelig were on the other station, which is commonly called 

 ZevenLoompjeSj or seven trees, from the circumstance of seven 

 tr^es being planted on this lonely elevation. Several gentlemen 

 cadets of the Artillery, and several students of the University, 

 were at both stations employed in observing the different 

 instruments* ; 



The barometers and thermometers were of course observed m 

 the open air ; Mr. Daniell's hygrometers were also placed in the 

 open air ; and the light of a candle reflected from the surface of 

 the ball of the hygrometer, gave the means of observing the 

 deposition of dew with great accuracy. .^ot>-, {)m 



; It was deemed of the utmost importance that the i^hpji9f,<^ 

 both stations should be fired at as nearly the same moment as 

 pg|ssible. To obtain this, the following plan was adopted. At 

 7^55' P.M. by the chronometer of Zevenboompjes, a rocket 

 wap fired at Zevenboompjes, which being observed at the other 

 sta,tion of Kooltjeshergj was immediately answered by another 

 rocket from the latter place. This was the signal that on both 

 stations every thing was ready for observation. At 8'^ 0' 0'^ by 

 the chronometer of ^ei;e«^oom/9;e5, a cannon shot was fii'ed on 

 that station, whilst the observers at Kooltjesberg took as exactly 



