VOL. XLIX.] PHILOSOPHICAL TRANSACTIONS. 587 



numerous in this scorched papyrus, and gives this copy to the Canon Mazzocchi, 

 who tries to supply the loss, and explain it. The letters are capital ones, and 

 almost without any abbreviation. The worst is, the work takes up so much 

 time, that a small quantity of writing requires 5 or 6 days to unroll, so that a 

 whole year is already consumed about half this roll. The lacunae, for the most 

 part, are of one or two words, that may be supplied by the context. As soon as 

 this roll is finished, they will begin a Latin one. There are some so voluminous, 

 and the papyrus so fine, that unrolled they would take up 100 palms space. 



XXIV. On the several Earthquakes lately felt at Constantinople. By James 



Porter, Esq. p. 115. 



This paper is quite unimportant, containing only some trite remarks on the 

 wind and weather, and accounts of some very trifling earthquakes that lately 

 happened, with no circumstances of any consequence. 



XXV. Letters of Henry Eeles, Esq. concerning the Cause of the Ascent of 

 Vapour and Exhalation, and those of Winds; and of the general Phenomena 

 of the fVeather and Barometer, p. 124. 



It is agreed, that the ascent of vapour and exhalation through the air may be 

 effected in two ways, by impulse, and an alteration of their specific gravity. 

 That vapour does not generally ascend by impulse, may be proved by many fami- 

 liar experiments, viz. put boiling water into a vessel; then empty it, and hold 

 the vessel with the aperture downwards; the vapour, which is afterwards expelled 

 from the vessel, must be in a direction downward; but we find, that as soon as 

 it has got but a very little below the rim of the vessel, it has its direction altered, 

 and ascends by the laws of specific gravity. The same thing may be observed in 

 all boiling vessels, where the vapour is emitted in a direction downward; or, in 

 cold weather, when the vapour of a man's breath may be seen, let him breathe 

 downward, and the direction of his breath will be presently altered, as in the 

 former case. Since then vapour ascends without any other impulse than that 

 which is incident on all bodies ascending by the laws of specific gravity; it is 

 necessary to inquire, how the specific gravity of vapour is altered, to cause its 

 ascent. This is generally supposed to be done by filling vesicles of water with 

 rarefied air, till the diameter of the vesicle be 10 or more times the diameter of 

 a drop of water, composed of the same constituent particles ; and that the vesicle, 

 by this means, becomes specifically lighter than air. But Mr. E. thinks that this 

 cannot be done so easily as it has been generally imagined; and when done, it 

 will not be sufficient for the purpose; which he infers from the following consi- 

 derations. First, the great difficulty in forming those vesicles, especially of the 

 particles of dry bodies carried off by exhalation, and filling them with rarefied 



4f 2 



