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which continue to rife from the bottom whilfl; even 
the water boils, and long after all the air is driven 
out of it. Dr. Boerhaave, in his Elements of Che- 
miflry, part II. has proved, by feveral arguments, 
that thefe bubbles do not arife from air ; and with 
regard to their produdion, he feems to be of the 
fame opinion with Stairs (to whofe work he refers) 
that they arife from lome adive fires refiding in the 
water. Mariotte, whom he alfo mentions on this 
occafion, calls thefe bubbles fulminations, and fup- 
pofes that they may arife from fome faline particles 
contained in the water, which being heated ad in 
the fame manner with the aurura fulminans. I find 
it is a received opinion (but how generally I cannot 
tell) that thefe bubbles are occafioned by fome fub- 
tile elaflic fluid, tranfmitted from the fire through 
the bottom of the vdlel. However, I conceive that 
the fluid fo fubtile as to pals readily through the 
bottom of the velTel, would pafs alfo through the 
water fo ealily as not diflurb it ; and, therefore, I 
liave for fome time fufpeded that thefe bubbles are 
formed only by an dajiic Jleaniy in the manner I 
lhall now deferibe. The particles on the furface of 
the water long before it boils, will, by means of 
the repelling force, which the heat introduces amongfl 
them, rife in fteam, and will infinuate themfelves 
into the air, which yields eafily to them ; but thofe 
particles that are prelfed againft the bottom, by the 
weight of the atmofphere, and of the incumbent 
water, will require a great degree of heat to render 
them fo elaftic, that they fliall be able to overcome 
this refiftance, and expand themfelves into a greater 
fpace. Now lince heat expands water, and makes 
