Dr. Venival on Attra5lion and RepuIJon. 447 



vyhich Sir Ifaac Newton fuppofes to pervade all 

 bodies. For, when this sther is excited into 

 motion, by percufilon or agitation, its elaftic 

 force is augmented, becaufe it becomes denfer 

 in the pulfesof its vibrations, than in a quiefcent 

 ftate. * But in propofing this hypothecs, I may 

 perhaps be chargeable with the paradoxical opi. 

 nion of a celebrated French philofopher, M. 

 Fontenelle, who afferts, that if there be more 

 than one way of accounting for any appearances in 

 nature, there is a general prefumpcion, that they 

 proceed from caufes, which are leafl obvious 

 and familiar. I fiiall not, therefore, at prefent, 

 enlarge upon this point, as it would anticipate 

 what may be better urged, in our fubfequent 

 converfation. But the fafts, above recited, fur- 

 ni(h a prefumptlon, that the effeft of oily fub- 

 ftances, on the cryflallization of fait, is, in part, 

 owing to a mechanical caufe. At Droitwich, 

 it is the practice, as appears by Dr. Wall's quo- 

 tation from the hiftory of Worcefterfhire, to 

 throw, into the brine pan, a piece of refin, about 

 the fize of a pea, to produce a finer granulation. 

 The more refin they ufe, the fmaller will be the 

 grain of the fait; and if a lump, of the fize of 

 two walnuts, were put into the pan, the particles 

 of fait would be fo minute as not to be capable 



* On the properties of ^ther, confult Dr. Bryan Robin- 



fon's Worlcs pajfun, 



of 



