356 PHILOSOPHICAL TRANSACTIONS. [anNO I7O7. 



were made reverse : so that I do not perceive that contrary motions any way 

 contribute to the phenomenon; but motion itself, without being prescribed 

 by rules, as this experiment seems to insinuate, is found absolutely necessary, 

 as indeed the whole course of experiments on this head abundantly confirm. 

 I further observe, that although the effluvia seemed to be equally distributed 

 on the the outer surface of the inner moving glass, yet the light was most vigo- 

 rously apparent on that side of it nearest the attrition: and when the motion 

 either of the outer or inner glass ceased, and the other in motion, (for upon 

 trial I found very little difterence either way,) the light would continue to 

 appear a considerable time within the exhausted glass, till the effluvia of the 

 other could no longer act with so much vigour, as to affect the inner one. I 

 likewise observed, that after both glasses had been for some time in motion, 

 and the hand applied all the while on the outer one, that then the motions 

 ceasing, and no light appearing, it was but approaching my hand near the 

 surface of the outer glass, to produce flashes of light like lightning in the 

 inner one, the effluvia seeming then to be m(»re vigorously pushed upon it by 

 the approaching hand. Now how these effluvia of glass became capable to act 

 or perform the office of a solid body, or why such a medium is required in 

 the inner glass to produce the light, I think are worthy the consideration of 

 the society. For I have tried, that upon letting in a little air, the appearance 

 of it died, nor could it then, by any means, be recovered in that state. 



An Experiment made before the Royal Society at Gresham College, May 28. 

 1707, shotving the Diffi,culty of separating two Hemispheres, on injecting an 

 Atmosphere of Air on their outward surfaces, without withdrawing the included 

 Air, By Mr. Fr. Hauksbee, F. R. S. N'^ 3 10, p. 2415. 



Since the greatest satisfaction and demonstration that can be given for the 

 credit of any hypothesis, is, that the experiments made to prove it, agree 

 with it in all respects, without force : as in that of sound, the air is proved to 

 be the proper vehicle to communicate it, not only by its lessening according to 

 the degrees of rarefaction, but by its increasing according to the degrees of 

 Qpndensation. Now although the pressure of the air is evident by a number 

 of undeniable experiments made with the air pump; yet the several phaenomena 

 of it, being liable to be accounted for the suctionists and funicularians, to 

 proceed from some unintelligible internal cause ; therefore to put the matter of 

 fact past ajl dispute, I devised the following experiment. 



y\ took a strong glass receiver, open and armed with brass hoops at top and 

 bottom; to which parts were applied two brass plates, with wet leathers between 

 them: but first were included two brass hemispheres, which joined on a wet 



