Winch on the Barometer. 243 



more striking, and, therefore, that " the influence of the 

 strongest wind ever known would not be quite insignificant." 

 The Professor continues, " Such is unquestionably the true 

 explication of the fact," and confirms it by this experiment : 



" Let A, Plate IV. Fig. 2. be any cylinder, suppose three 

 inches long, and two in diameter, having an open pipe insert- 

 ed at B, a quarter of an inch wide, and perhaps two inches 

 long, and another at C about three-eighths or half an inch 

 wide, and one inch long ; at right angles to these a syphon 

 GHF of one-tenth of an inch bore is cemented below contain- 

 ing coloured water. If a blast be injected into the cavity at 

 B, the water will rise to G, showing the diminished pressure, 

 and consequent rarefaction of the air above it ; but if a cap D 

 with a narrow pipe of perhaps one-eighth of an inch bore be 

 adapted to C, on repeating the experiment, an opposite effect 

 will take place, and the column of water will subside to H. 

 It is evidently the difficulty of the escape through D which 

 occasions the accumulation of air in the cylinder.'' 



The reason given in the latter case is undoubtedly just, but 

 not so in the former ; for to produce a rarefaction of the air 

 in the cylinder, it is necessary that more air should pass out 

 through C than is injected at B, an incident which we cannot 

 look for. 



I will now show that the wind may partially remove or in- 

 crease the vertical pressure according to its direction. 



Let AB, Fig. 3. be any tube of equal bore, into the side of 

 which the syphon CE containing coloured water, opens at an 

 angle of about 30° with the tube AB ; now, if a blast be sent 

 through the tube from A to B, the column in C will fall, if 

 from B to A, the column will rise, and even flow out through 

 the tube AB, the latter result will take place, whatever the situ- 

 ation of the tube C, provided the blast does not take effect 

 down the opening of C, for then the column will be depressed. 



These latter proofs of the action of the wind were suggest- 

 ed by an article in a late number of the " Mechanics' Maga- 

 ::inc^ in which the writer says he raised water to the height of 

 eight inches in a funnel by the blast of a pair of bellows di- 

 rected over the mouth of it. I have since found the princi- 

 ple of much service in the use of a syphon, for by directing a 

 blast from the mouth through a tube rather larger than tin- 



