4|a DISEASES OF IRRITATION. SECT. XXXI). t. 



moon (allowing for the time necefTary for their 

 xriotion, and the obihucYions of the fhores), it is 

 probable, that there are alib atmofpheric tides on 

 both fides of the earth, which to the inhabitants 

 of another plane* might fo defied the Jight as to 

 referable the ring of Saturn. Now as thefe tides 

 of water, or of air, are railed 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^there- 

 fore that they cannot affeclt the mercury in the 

 barometer. In the fame manner, the gravity in all 

 ^ther terreftrial bodies is cjiminifhed at the times 

 pf the fouthing and northing of the niopn, and that 

 ma greater degree w.htn- this coincides- with the 

 ibuthing and northing of the fun^ and this in a 

 ftill greater degree about the times of the equi- 

 noxes* This decreafe of the gravity of all 'bodies 

 during the time the moon pafTes our zenith^ 'or 

 nadir might poffibly be fhewn by the flower vi- 

 brations of a pendulum,- compared with a fpring 

 clock, or with : aftronomjcal obfervation. Since a 

 pendulum of a certain length moves flower at the 

 line than near the poles, becaufe the gravity being 

 diminifhed and the vis inertias continuing the fame, 

 the motive power is lefs, but the refinance to be 

 overcome continues the fame. Tfie combined pow- 

 ers of the lunar and folar attraction is eftimated 

 by Sir Ifaac Newton not to exceed one 7,868, 5oth 

 part of the power of gravitation, which feems in- 

 deed but a fmail circumftance to prpduce any con- 

 iiderable effedj: on the weight of fublunary bodies, 

 and yet this is fufficienjt to raife the tides at the 

 equator above ten feet high ; and if it be conii- 

 dcred, what frnall impulfes of other bodies produce 

 their effedls on the organs of fenfe adapted to the 

 perception of them, as of vibration on the aucji- 



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