138 Remarks on Dr. Enfield's Institutes 



which is effective to the ratio of the cube of the sine, instead 

 of the square.* But as the variation of the force deter- 

 mined from experiment differs totally both from the square 

 and the cube, it would hav^e been better to erase the propo- 

 sition, than to attempt to amend it. 



Prop. 53. Schol. The mode in which the constant ve- 

 locity of sound is attempted to be explained, (which, like 

 the rest of the scholium, is copied from Rowning,) is whol- 

 ly erroneous : nor do we think it easy to substitute an un- 

 exceptionable theory of the mechanism of aerial pulsations, 

 without involving mathematical principles of a higher order 

 than the student is supposed to be acquainted with. 



Prop. 56. Schol. 3. "It is found by experiment, that 

 air is necessary to the existence of sound, of animal life, of 

 lire, and of explosion." This, like several other statements 

 scattered up and down the work in which chemical princi- 

 ples are alluded to, needed correction to render it accord- 

 ant with the present state of our knowledge on these sub- 

 jects. The experiments of Biot and Chladni shew that 

 gound is transmitted by solid bodies as well as gaseous ones, 

 and that it may be conveyed to the organs of hearing with- 

 out the intervention of air, by forming a communication 

 between the sounding body and the head by means of a 

 solid conductor. — That fire and explosion require air for 

 their existence, is true only in the most loose and popular 

 sense of the terms. In particular, that the explosion of 

 gunpowder cannot be effected in a vacuum, as is implied in 

 one of the annexed experiments, is an entire mistake.f 



The articles on the barometer, thermometer, hygrometer, 

 and steam-engine, are extremely defective in point of valu- 

 able information, compared with what might have been sgid 

 about them within the same limits, and in several respects are 

 calculated to leave erroneous impressions : but we must 

 content ourselves with giving this general caution against 

 placing implicit confidence in them. J 



* This theoretical detcrmiaalion may be seen, Grecrory's Mechanics, I. 

 539, &c. 



f Robins, HiiUon's Math. Dictionary, k.v.. 



X If may be proper just to state, for (he information of those who may 

 have access to no other ruie than that given page 110, in making loose esli- 



