278 Dr, Moll on the [Oct. 



u 



^11^0,00375.} X y^i.o,3765l)i'. 



The 27th of June, 1823, we had 



U = 340'",06 = 1116,032 English feet 

 t = W, 16 cent, 

 F = 0,00925307 

 p = 0,74475 metres. 



Substituting these quantities in the formula, we have 



U'= 332'",38 = 1090,827 English feet. 



The 28th June, 1823, we had 



U = 339™,34 = 1113,669 feet 

 t = 1P,215 

 F = 0,00840465; 



which being substituted in the formula, we have 



V'=z 331V2 = 1088,661 English feet. 

 Thus the difference between the observations of both days, 

 when reduced to dry air, and 0° cent, is 0'",66 = 2,166 feet ; 

 or y^ of the mean of the observations of both days. It 

 appears also, that by our experiments of the 27th and 28th 

 of June, 1823, the mean velocity of sound in air perfectly 

 dry, and at 0° temperature, was 332^^,05 = 1089,744 feet in a 

 second. 



Experiments on the 25th of June, when the Shots were not reci- 

 procal. 



The following experiments will I trust prove, that in experi- 

 ments on the velocity of sound, such observations can only be 

 relied on in which the shots on both stations were reciprocal, that 

 is fell within the same second in both places, and were equally 

 heard and seen on both stations. The 25th of June, the cannon 

 fired at Zevenboompjes was not heard at Kooltjesberg, but at 

 Zevenboompjes the report of the guns fired at the other place 

 was distinctly perceived. The following table shows the time 



reterlapsed between the light and report, as observed at 



evenboompjes. 



I' 



