4^2 Dr. TVall on AttraSfion and Repulfioni 



*this circumftance, that the experiment fucceecid 

 beft with the fineft needles, and if we repeat 

 it fuccefiively with different needles, of different 

 fizes, from the fmallefl: to the largefl,- we fhall 

 find the experiment more and more difHculr,- 

 and at lad impracticable; becaufe, although in 

 the fmaller needles the bulk of the whole bears 

 comparatively a very fmall proportion to the 

 extent of their furface ; in the larger needles this 

 is not the cafe, and, therefore, the common 

 law of fpecific gravity takes place, and the 

 needle finks in the water. I have paid a good 

 deal of attention to this experiment, both with 

 the naked eye, and with a magnifier, and cannot 

 fay that I am fatisfied, that Mr. Mehill is ac- 

 curate in afferting, that the needle is not in 

 contaft with the water. It forms indeed, as he 

 fays, a bed for itfelf^ and depreffes the water, 

 but, if we obfcrve minutely, we fee that the 

 water touches the lower furface or fides of the 

 needle in many minute points. Why the water 

 does not come into more general contaft with the 

 needle, depends probably upon the fame caufe 

 that difpofes water to form, globules upon the 

 furface of any highly polifhed metal, or almofl 

 any other inflammable fubflancc : and to the 

 explanation of this point the fame principles of 

 chemical attraction, fa largely infifted upon 

 in this and my former letter, lend their aide 

 Water, and all watery fluids, have little or no 



attraftioR 



