Sect. XXXII. 6. i. OF IRRITATION. 793 



neoufly relieve thofe nervous pains, which attend the cold peri- 

 ods of hyfteric, afthmatic, or epileptic difeafes ; and that even 

 where large dofes of opium have been in vain exhibited. In 

 thefe cafes the pulfe becomes ftronger after the bleeding, and 

 the extremities regain their natural warmth ; and an opiate then 

 given acts with much more certain effect. 



VI. There is another caufe, which feems occafionally to in- 

 duce quiefcence into fome part of our iyftem, I mean the influ- 

 ence of the fun and moon -, the attraction of thefe luminaries, 

 by decreafing the gravity of the particles of the blood, cannot af- 

 fect their momentum, as their vis inertix remains the- fame ; 

 but it may neverthelefs produce fome chemical change in them, 

 becaufe whatever affects the general attractions of the particles 

 •of matter may be fuppofed from analogy to affect their fpecific 

 attractions or affinities : and thus the flimulus of the particles 

 of blood may be diminiihed, though not their momentum. As 

 the tides of the fea obey the fouthing and northing of the moon 

 (allowing for the time neceffary for their motion, and the ob- 

 ilructions of the fhores), it is probable, that there are alfo at- 

 mofpheric tides on both fides of the earth, which to the inhab- 

 itants of another planet might fo deflect the light as to refemble 

 the ring of Saturn. Now as thefe tides of water, or of air, are 

 raifed by the diminution of their gravity, it follows, that their 

 preffure on the furface of the earth is no greater than the preffure 

 of the other parts of the ocean, or of the atmofphere, where no 

 fuch tides exift ; and therefore that thev cannot affect the mer- 

 cury in the barometer. In the fame manner, the gravity of all 

 other terreftrial bodies is diminiihed at the times of the fouth- 

 ing and northing of the moon, and that in a greater degree when 

 this coincides with the fouthing and northing of the fun, and 

 this in a ftill greater degree about the times of the equinoxes. 

 This decreafe of the gravity of all bodies during the time the 

 moon paffes our zenith or nadir might poffibly be (hewn by the 

 flower vibrations of a pendulum, compared 1 with a fpring clock, 

 or with aftronomical obfervation. Since a pendulum of a cer- 

 tain length moves flower at the line than near the poles, becaufe 

 the gravity being diminiihed and the vis inertia? continuing the 

 fame, the motive power is lefs, but the refiftanceto be overcome 

 continues the fame. The combined powers of the lunar and 

 folar attraction are eftimated by Sir Ifaac Newton not to exceed 

 one 7,868,850th part of the power of gravitation, which feems 

 indeed but a fmall circumftance to produce any considerable ef- 

 fect on the weight of fublunary bodies, and yet this is fufficient 

 to raife the tides at the equator above ten feet high ; and if it be 

 confidered, what fmall impulfes of other bodies produce their 



effects 



