PNEUMATICS. 289 



Princip. Math. lib. ii. prop. 47. & 49- The sound- 

 ness of this reasoning, however, was questioned by 

 EULER ; and it was afterwards shewn by CRAMER, 

 that the same argument might be used to prove 

 conclusions very different from that at which NEW- 

 TON had actually arrived. Commentary on the Prin- 

 cipia, lib. ii. vol. ii. p. 364. LA GRANGE after- 

 wards gave an accurate solution of the problem, by 

 which, though he pointed out the error of NEW- 

 TON'S reasoning, he confirmed the truth of his 

 conclusion. 



389. The velocity of the pulses propagated in 

 an elastic fluid, are as the square root of the elasti- 

 city divided by the density of the fluid. 



Prin. Math. ibid. prop. 48. 



The velocity of sound, computed as in the last ar- 

 ticle, comes out less than by actual experiment. 

 LA PLACE has suggested a very probable explana- 

 tion of this, viz. that the condensation of the undu- 

 Ice, which must take place in these vibrations, pro- 

 duces a degree of sensible heat, by which the elas- 

 ticity is increased, or, to speak more correctly, the 

 density diminished, while the elasticity remains the 

 same. The heat required for that effect has 

 been shewn by BIOT to be within the probable li- 

 mits which analogy, in the absence of direct expe- 

 riment, would lead us to assign. HAUY, Lemons de 

 Phys. 478. 



VOL. I. T 390. There 



