t52 ESSAYS AND OBSERVATIONS' 



put in motion amongft themfelves ; or^ 

 in other words, unlefs the folid body was 

 converted into a fluid. A parcel of dry* 

 fand may bear fome fmall refemblance to 

 a fluid ; its particles may be moved more 

 eafily amongft one another than thofe 

 of a firm body, whofe parts are clofely 

 united by attradlon: Yet ftill there muft 

 be a confiderable adhefion of the particles 

 of fand, on account of their irregular fi- 

 gures, and the inequalities on their furfa- 

 ces. When a man applies his hand to a 

 hole in the fide of a vefTel of water, he 

 fuftains a prefiure from the tendency of 

 the particles to Aide down and make their 

 efcape : But, when his hand is laid on the 

 fide of a fand-bank, there is no fuch pref- 

 fure to be felt ; becaufe the particles aref 

 intangled together, and fupport one ano- 

 ther. Thus a body laid upon a rough in- 

 clined plain, may remain fixt, by the re« 

 fiftance from attrition alone ; whereas, if 

 the plain be fmooth, fome other power 

 becomes neceflTary to hinder the defcent 

 of the body. 



The ; 



