455 
the velocity of sound , made in Holland. 
Mean atmospheric pressure at Zevenboompjes o'", 7493. 
Mean atmospheric pressure at Kooltjesberg o m ,75i2. 
Mean pressure of atmosphere 0,75025 = p. 
Mean tension of aqueous vapour at Zeven-1 
. . v 0,00892922 
boompjes ) 
at Kooltjesberg 0,01011376 
Mean tension of aqueous vapour . 0,00952149 = F 
Calculating by this datum we shall have the observed 
velocity of sound in T reduced to dry air and o° tempera- 
ture V= 338™, 20 = 1109,927 feet; but the experiments of 
the 25th gave V' = 331, “85 = 1089,087 feet. Difference 
6 m ,35 = 20,840 feet per 1" between the experiments of the 
25th and 26th of June, in which the shots were not recipro- 
cal. This difference is about of the mean of both obser- 
vations. But the 27th and 28th of June, when the shots were 
reciprocal, the difference between the results of both days 
were only o m ,66=: 2,166 feet, that is about of the mean 
result of the observations. 
From the comparison of these results we may safely infer, 
that only such shots will answer the purpose for which these 
experiments are made, which are exactly fired at the same 
instant on both stations. 
It is in this respect, I imagine, that our experiment 
may claim some attention, as the very great care and ability 
of our artillery men enabled us have the guns fired within 
the interval of one second. 
