6 OFMOTION. SECT. I. 



there is neverthelefs a fourth divifion of motions ; 

 I mean thofe of the fuppofed ethereal fluids of mag- 

 netifm, electricity, heat, and light ; whofe proper- 

 ties are not fo well inveiligated as to be claffed with 

 fufficient accuracy. 



ift. The gravitating motions include the annual 

 and diurnal rotation of the earth and planets, the 

 flux and reflux of the ocean, the defcent of heavy- 

 bodies, and other phenomena of gravitation. The 

 unparalleled fagacity of the great NEWTON has de- 

 duced the laws of this clafs of motions from the 

 iimple principle of the general attraction of matter. 

 Thefe motions are diftinguiftied by their tendency 

 to or from the centers of the fun or planets. 



id. The chemical clafs of motions includes all 

 the various appearances of chemiftry. Many of the 

 fads, which belong to thefe branches of fcience, are 

 nicely alcertained, and elegantly clafled ; but their 

 laws have not yet been developed from fuch fimple 

 principles as thofe above-mentioned ; though it is 

 probable, that they depend on the fpecific attracti- 

 ons belonging to the particles of bodies, or to the 

 difference of the quantity of attraction belonging 

 to the fides and angles of thofe particles. The che- 

 mical notions are diftinguifhed by their being gene- 

 rally attended with an evident decompolition or 

 new combination of the active materials. 



3^/. The third clafs includes all the motions of the 

 animal and vegetable world ; as well thofe of the 

 veffels, which circulate their juices, and of the 

 rnufcles, which perform their locomotion, as thofe 

 of the organs of fenfe, which conftitute their ideas. 



Thib laft clafs of motion is the fubject of the fol- 

 lowing pages ; which, though confcious of their 

 many imperfections, 1 hope may give fome pleafure 

 to the patient reader, and contribute fomething to 

 the knowledge and to the cure of difeafes. 



SECT. 



