134 Remarks on Dr. Enfield's Institutes 



evidence of a repulsive power in bodies, that they are mere 

 examples of cohesion, modified by circumstances. If we 

 suppose the force of aggregation between the particles of 

 mercury to be more than ?w?ce their force of cohesion to 

 iron and to glass,* it appears from the investigations of 

 Clairaut, that a depression ought to be the consequence.™ 

 The suspension of a small needle on water is owing to a 

 certain degree of viscidity in this fluid, — in consequence of 

 which the particles of the uppermost stratum present more 

 resistance to separation than can be overcome by the down- 

 ward pressure of the needle. Those who are acquainted 

 with the extended researches of Count Rumford on this sub- 

 ject, will find no more reason for ascribing the support of a 

 needle on water to a positive repellency, than the support of 

 a cannon ball on ice. Both are alike owing to the cohe- 

 sion of the upper surface. The only difi;erence is, that as 

 the cohesion is many times the least in the former case, the 

 weight of the supported body must be proportionally less, 

 when compared with the surface it exposes. 



Book II. Prop. A. This proposition, (besides that the 

 demonstration is unsatisfactory,) is out of place ; as the 

 chapter is confined by its title to the comparison of uniform 

 motions. It ought to have been deferred to ch. v. 



Prop. 22. Cor. 1. is evidently erroneous. A second 

 " Cor. 1." is inserted under this proposition, which belongs 

 to the preceding one ; for it is true only of non-elastic bod- 

 ies. 



Prop. 30. The demonstrations of the laws of oblique de- 

 scent in the annexed corollaries, are rendered unnecessarily 

 obscure by changing the denomination of the entire force of 

 gravity, which was F in the preceding section, to unity. In 

 a subsequent demonstration relating to the pendulum it is 

 again changed to A. We mention these changes, not as 

 involving any thing positively erroneous ; but as an illustra- 

 tion of our general remark concerning the want of care in 

 the compiler, to reduce the notations of the different authors 

 from whom he borrowed, to a common standard. 



Prop. 37. The demonstration is defective, from not being 

 extended, as it easily might be, to the supposition that mo- 



* Pei'liaps it ought rnlbei- to be said; — to " the film of mohlurz which i;5 

 ordinarily attached to ll'.c svnrace ofgla-ss." ?ee Haijy — Traito de Fiiyviqut;; 

 1.225. Biot—l, 4;>r). 



