328 PHILOSOPHICAL TRANSACTIONS. [aNNO 1729. 



their contact, the repulsion grows stronger, and the particles exert that force 

 at great distances ; so that the same body shall be expanded into a very large 

 space by becoming fluid, and may sometimes take up more than a million of 

 times more room than it did in a solid or incompressible fluid. (See the Queries 

 at the end of Sir Isaac Newton's Optics.) Thus is water by boiling, and less 

 degrees of heat, changed into an elastic vapour, rare enough to rise in air; oils 

 and quicksilver in distillation are made to rise in a very rare medium, such as 

 remains in the red-hot retort; and sulphureous steams will rise even in an ex- 

 hausted receiver, as the matter of the aurora borealis does in the thinner part of 

 the atmosphere. If aquafortis be poured on quicksilver, a reddish fume will 

 rise, much lighter than common air; so also will fumes rise from filings of 

 metals, from vegetables when they ferment by putrefaction; and, as Mr. Hales 

 has shown, several solid substances by distilling, as well as fermentation, will 

 generate permanent air. 



That heat will add elasticity to fluids, is evident from numberless experiments, 

 especially from distilling and chemistry: but what is needful to consider here, is 

 only that it acts more powerfully on water than common air; for the same heat 

 which rarefies air only f, will rarefy water very near 14000 times, changing it 

 into steam or vapour as it boils it: and in winter, that small degree of heat, 

 which in respect to our bodies appears cold, will raise a steam or vapour from 

 water, at the same time that it condenses air. 



By a great many observations made by Mr. Henry Beighton, F. R. S. and by 

 the Doctor, on the engine to raise water by fire, according to Mr. Newcomen's 

 improvement of it, they found that the water in boiling is expanded 14000 

 times, to generate a steam as strong (i. e. as elastic) as common air, which there- 

 fore must be near l6-|- times specifically lighter. And that this steam is not 

 made of the air extricated out of the water is plain, because it is condensed 

 again into water by a jet of cold water spouting in it; and the little quantity of 

 air that comes out of the injected water must be discharged at every stroke, 

 otherwise the engine will not work well. There is also another experiment to 

 confirm this, as follows. 



Exper. 1 . — ABCD, fig. 5, is a pretty large vessel of water, set on the fire to boil. 

 In this vessel must be suspended the glass bell e, made heavy enough to sink 

 in water, but put in, in such a manner that it be filled with water when upright, 

 without any bubbles of air at its crown within, the crown being all under water. 

 As the water boils, the bell will by degrees be emptied of its water, being 

 pressed down by the steam which rises above the water in the bell; but as that 

 steam has the apptarance of air, in order to know whether it be air or not, take 

 the vessel off the fire, and draw up the bell by a string fastened to its knob at 



