1 OF MOTION. Sect. L 



to have caufed the projection of the planets from the fun, and 

 to prevent their relapfe into one chaotic mafs. Thefe motions 

 are diftinguifhed by their tendency to or from the centres of the 

 fun or planets. 



id. The chemical clafs of motions includes all the various ap- 

 pearances of chemiftry. Many of the facts, which belong to 

 thefe branches of fcience, are nicely afcertained, and elegantly 

 claffed ; but their laws have not yet been developed from fuch 

 fjmple principles as thofe above mentioned ; though it is prob- 

 able, that they depend on the fpecific attractions belonging to 

 the particles of bodies, or to the difference of the quantity of at- 

 traction belonging to the fides and angles of thofe particles, to 

 which fhould perhaps be added the fpecific repulfions belonging 

 to the particles of bodies. When thefe repulfions prevail over 

 the attractions, they may caufe the diffusions of light and of 

 odours, the explofions of fome bodies, and the flower decompo- 

 sition of others, and occafion our ideas of fluidity ; when the 

 attractions prevail over the repulfions, they may caufe the ftrict- 

 er combinations and cohefions of matter, as in cryftalization or 

 cooling, and give rife to our ideas of folidity ; and when thefe 

 two caufcs of motion are in active equilibrium, they may pro- 

 duce the vibrations of the particles of bodies, and occafion our 

 ideas of found. The chemical motions are diftinguifhed by their 

 being generally attended with an evident decompofition or new 

 combination of the active materials. 



%d. The third clafs includes all the motions of the animal and 

 vegetable world ; as well thofe of the vefTels, which circulate 

 their juices, and of the mufcles, which perform their locomotion, 

 as thofe of the organs of fenfe, which conftitute their ideas. 



This lafl clafs of motion is the fubject of the following pages ; 

 which, though confcious of tHeir many imperfections, I hope 

 may give fome pleafure to the patient reader, and contribute 

 fomsthing to the knowledge and to the cure of difeafes. 



SECT- 



