340 Transactions of the Society. 



a laboratory caoutchouc cap with two tubes; into the smaller or 

 neck end fits air-tight a short (1^ inch) ground metal tube. 



The two aeroscopes are fixed to a small base-board by two stout 

 indiarubber bauds, which pass through two saw- cuts at each end of 

 the board. This board is fastened on the top of a 5^-feet tripod 

 stand. A bladder or a small can containing a certain quantity of 

 water is hooked to the under surface of the board, a flexible siphon 

 tube dips into the water, reaching to the bottom of the vessel, the 

 long leg of the siphon being fitted with a small stopcock with a 

 long conical nozzle. On the lower end of the short metal tube of 

 the aspirator is fitted an indiarubber tube about 9 inches long and 

 2-8ths of an inch bore ; a complete loop is turned on the tube 

 almost close to the metal tube, being held in place by a letter S 

 zinc clasp ; the other end of the tube shps over a piece of glass 

 tube of the same bore, about 9 inches long, this forming the index- 

 tube. To the lower end of this glass tube is adapted another 

 caoutchouc tube, which at the opposite end fits on a small stopcock 

 fastened into and passing through the neck of a second bladder, 

 which in use rests on the floor against one of the legs of the tripod. 

 In the neck of the same bladder is a short metal tube, to which is 

 fixed another indiarubber tube that leads to and is fixed on a small 

 stopcock secured in the neck of a third and much larger bladder, 

 suspended by its neck, with stout twine, between the legs of the 

 tripod. The stopcock tube and the second tube are best soldered 

 into a brass tube before it is fixed in the neck of the second bladder ; 

 corks do not answer well. The exit ends of the aeroscopes are 

 each joined by caoutchouc tubes to the spread branches of a 

 Y-shaped metal tube, the lower end of which fits into one of the 

 two tubes of the indiarubber cap of the little aspirator, which is 

 held at a convenient height against one of the legs of the tripod 

 by a couple of elastic bands. All the junctions must be made air- 

 tight, and the top of the wooden aeroscope screwed down upon an 

 indiarubber or greased leather washer. 



In use, the bladder or small vessel. No. 1, with its siphon, is 

 filled with water, wholly or partially, and suspended from the under 

 surface of the small base-board. The siphon being made to act by 

 suction, and its stopcock turned ofi", the conical end of the nozzle is 

 at once fitted into the unoccupied tube of the cap of the aspirator. 

 The two other bladders (No. 2 and No. 3) are squeezed empty of air, 

 and their stopcocks turned off and fitted to their respective tubes. 

 The stopcock of the siphon is now opened, so that a drop of water 

 may either drop at the rate, say of 70 to 100 per minute, or else 

 trickle along the side of the little aspirator ; this, I think, gives more 

 uniform results than when dropping. The stopcocks of the other 

 two bladders are at once opened. The slow dripping of the water 

 into the looped tube sucks over a considerable amount of air which 



