VOL. v.] PHILOSOPHICAL TRANSACTIONS. 481 



But though I was at first content to make use of this way of estimating the 

 air concealed in water, yet when I came where I could be a little better accom- 

 modated with glasses, I bethought myself of a small instrument, that would 

 much better disclose the quantity of the aerial particles I designed to discover. 

 The structure and use of this glass may be easily enough understood by the reci- 

 tal of the first experiment that was made with it, as follows: 



We provided a clear round glass, with a pipe or stem of about nine inches in 

 length, the globular part of the glass being on the outside about 3-y inches in 

 diameter; the pipe of this glass was, within an inch of the top, melted at the 

 flame of a lamp, and drawn out for two or three inches as slender as a crow's 

 quill, that the decrement of the water upon the recess of the air harboured in 

 its pores, might, if any should happen, be the more easily observed and esti- 

 mated. Above this slender part of the pipe, the glass, as was before intimated, 

 was of the same size (or near it) with the rest of the pipe, that the aerial 

 bubbles, ascending through the slender part, might there find room to break, 

 and so prevent the overflowing or loss of any part of the water. 



This vessel being, not without difficulty and some industry, filled, till the li- 

 quor reached to the top of the slender part, where not being uniformly enough 

 drawn out, it was somewhat broader than elsewhere, we conveyed the glass, 

 together with a pedestal for it to rest upon, into a tall receiver, and pumping 

 out the air, numerous bubbles disclosed themselves, ascending nimbly to the 

 upper part of the glass, where they made a kind of froth or foam ; but by rea- 

 son of the above-mentioned figuration of the vessel, they broke at the top of 

 the slender part, and so never overflowed. 



This done, the pump was suffered to rest a while, to give the aerial particles 

 lodged in the water time to separate themselves and emerge, which when they 

 had done a pretty while, the pump was plied again, for fear some air should 

 have stolen into so large a receiver. These vicissitudes of pumping and resting 

 lasted for a considerable time, till at length the bubbles began to be very rare, and 

 we weary of waiting any longer ; soon after which the external air was let into 

 the receiver, and it appeared somewhat strange to the spectators, that notwith- 

 standing so great a multitude of bubbles as had escaped out of the water, I could 

 not, by attentively comparing the place where the surface of the water rested at 

 first with that where it now stood, discern the difference to amount to above a 

 hair's breadth, if so much, and the chief operator in the experiment professed 

 that, for his part, he could not perceive any diflference at all. 



Thus far for the narrative of the trial made by water ; but that was not the 

 only liquor into whose aerial particles I designed by our little instrument to in- 

 quire ; and therefore filling a glass of the same shape, and much of the same 



VOL. I. 3 P 



