NOTES. 



459 



Fig. 41. 



wine, in a capillary tube, is hollow ; and that of a column of quicksilver 

 is convex, or rounded, as in fig. 41. 



NOTE, 173, p. 113. Inverse ratio, fyc. The elevation of the liquid 

 is greater in proportion as the internal dia- 

 meter of the tube is less. 



NOTE 174, p. 114. In fig. 41 the line 

 c d shows the direction of the resulting force 

 in the two cases. 



NOTE 175, p. 115. When two plates of 

 glass are brought near to one another in water, the liquid rises between 

 them ; and, if the plates touch each other at one of their upright edges, 

 the outline of the water will become an hyperbola. 



NOTE 176, p. 115. Let A A', fig. 42, be two plates, both of which are 

 wet, and B B' two that are dry. When partly immersed in a liquid, its 



surface will be curved close to them, but will be of its usual level for the 

 rest of the distance. At such a distance they will neither attract nor 

 repel one another. But, as soon as they are brought near enough to have 

 the whole of the liquid surface between them curved, as in a a', b b', they 

 will rush together. If one be wet and another dry, as C C', they will 

 repel one another at a certain distance ; but, as soon as they are brought 

 very near, they will rush together, as in the former cases. 



NOTE 177, p. 123. In a paper on the atmospheric changes that produce 

 rain and wind, by Thomas Hopkins, Esq., in the Geographical Journal, 

 it is shown that, when vapour is condensed and falls in rain, a partial 

 vacuum is formed, and that heavier air presses in as a current of wind. 

 Thus the vacuum arising from the great precipitation at the tropics causes 

 the polar winds to descend from the upper regions of the atmosphere and 

 blow along the surface to the equator as trade winds to supply the place 

 of the hot currents that are continually raising them into the higher regions. 

 This circumstance removes the only difficulty in Lieutenant Maury's 

 theory of the winds. 



NOTE 178, p. 134. Latent or absorbed heat. There is a certain 

 quantity of heat in all bodies, which cannot be detected by the ther- 

 mometer, but which may become sensible by compression. 



x 2 



