Dr. R. Hare on the Explosiveness of Nitre, 525 



1 inch per second on velocities varying from 1 foot 9 inches 

 to 4- feet 6 inches per second ; and in the case of the large 

 waves, the error is 1| inch per second. This discrepancy, 

 moreover, is on the right side; as viscidity and friction have 

 undoubtedly some influence, although slight, and will make 

 the actual velocity less than a theory which does not recognize 

 them can assign. 



In order to determine whether anything was due to vis- 

 cidity, the author tried the following experiment : — In a 

 trough 2 feet 2 inches long by 1^ inch wide, a wave was 

 generated, by pushing down at one end a block of wood, 



2 inches long and of a width equal to that of the trough, first 



in water, then in linseed oil. The distance, then, for the wave 



to travel was 2 feet exactly. The quantities of water and oil 



were measured in the same vessel, and therefore the depths 



were the same, and all circumstances alike except the nature 



of the fluid. In the water the undulation could be distinctly 



perceived after the wave had travelled 128 feet, but in the oil 



it was only just perceptible when it had travelled but 12 feet. 



The time occupied by the wave in the water in passing over 



the above distance was 1 minute ; by the wave in the oil in 



passing over 12 feet, fully 6 seconds. Taking it at 6 seconds, 



12 1 28 



-— = 2 feet per second. Water wave — — =2*13 feet per 

 6 60 



second. 



The height was, as nearly as could be ascertained, 1*65 inch, 

 which would give a velocity of 2*104 feet per second: much 

 dependence, however, could not be placed on this measure- 

 ment. 



The accompanying diagram (Plate III.) is half of the wave, 

 No. 7 of the large waves, laid down full size from calculation 

 by the formula (10.), assuming the length to be 7r(a-{-#). 



LX XII. On the Explosiveness of Nitre, with a view to elucidate 

 its agency in the tremendous explosion of July 1845, in New 

 York. By Robert Hare, M.D., Emeritus Professor of 

 Chemistry in the University of Pennsylvania, and Associate 

 of the Smithsonian Institution*. 



1. 4 MONG the conflagrations by which cities have been 



-^- more or less devastated, there has been none, it is 



believed, of which the phaenomena were more awful and 



* This memoir forms one of the Smithsonian Contributions to Knowledge, 

 and was accepted for publication by the Institution, October 1849. For its 

 communication we are indebted to the kindness of the Author. 



