272 Dr. Moll on the [Oct. 



as possible the lime on their chronometer when the light was 

 observed. A second shot was fired atZevenboompjes atH" 5' 0'' 

 P. M. by the chronometer of that station, and the time at which 

 the light was seen was carefully taken down by tlie chronometer 

 of Kooltjesberg. By these means the difference of the two 

 chronometers at both stations, in a distance of about nine miles, 

 was ascertained with great accuracy ; and in order to show that 

 this preparatory investigation was made with due care, a cannon 

 shot was fired on both places at the moment when the chrono- 

 meter of Zevenboompjes marked 8'' 10' 00'^ If the lights of 

 both shots were seen exactly at the same time, it was a proof 

 that the difference of both time-keepers was known, and that 

 experiments might be safely made. 



We own that we did not suppose before hand, that it could 

 be possible to fire continually guns at a distance of nine miles 

 exactly at the same second ; but the very great attention and 

 ability of our artillery men overcame this difficulty. Between 

 our shots at the two stations there was never a greater difference 

 than V^ or 2'', whilst this difference in the experiments of the 

 French philosophers of 1822, went to five minutes. This exact 

 correspondence in the firing of the guns was obtained in the 

 followmg manner. At each station an officer had the chrono- 

 meter placed before him on a small table very near the gun ; a 

 non-commissioned officer or gentleman cadet stood ready with 

 the port fire near the touch-hole ; and at the instant required 

 the officer holding the chronometer pressed the arm of the per- 

 son who was to fire the gun, which went off at the very moment. 

 With a little practice they were certain to fire the gun at any 

 given second. 



The first night of our experiments, the 23d, 24th, and 25th of 

 January, 1823, we experienced the same annoyance of which 

 the French philosophers had to complain the first night of 

 theirs. The report of the shots of Zevenboompjes was not 

 heard at all at the station of Kooltjesberg. But at Zeven- 

 boompjes all the shots of Kooltjesberg were distinctly heard. 

 After the first night we constantly used the metal twelve poun- 

 ders loaded with Gibs of gunpowder. The 26th of January all 

 the shots were heard at Kooltjesberg, but none were perceived 

 at the opposite place. But the wind shifting the following 

 night, a good number of corresponding or simultaneous shots 

 were distmctly heard on both stations. The particulars of the 

 experiments made in these different days will be found in the 

 tables annexed to this paper. The disappointment we met 

 with on the first days was however not entirely fruitless ; we 

 were convinced by it, that none but exactly corresponding shots 

 can be of use in determining the velocity of sound. The result 

 of the observations of 26th and 26th of January, when the 

 reports were heard at one station only, and reduced to 0° tem- 



