196 NITROGEN. 



Mr. Perkins states, that he has applied to it a pressure of 2000 

 atmospheres, and he supposed that he had thus compressed it into a 

 liquid, but as this liquid was permanent under the common pressure, 

 it is probable it was water only. As we descend below the surface of 

 the earth, the density and pressure of the air continue to increase 

 in the same ratio. " In very deep mines, water will not boil till heat- 

 ed 3 or 4 degrees above 212*. Murray. 



(g.) The greater part of the atmosphere is within three or four 

 miles of the earth's surface. 



(h.) The phenomena of refraction indicate that the atmosphere is 

 at least forty or forty five miles high. 



(i.) Dr. Wollaston thinks that the atmosphere has limits fixed by 

 gravity, counteracting the elasticity imparted by caloric, (Phil. Trans. 

 1822,f) and on account of the absence of refraction, (the heavenly 

 bodies not being disturbed in their apparent position,) it is asserted 

 that neither the sun nor Jupiter has any atmosphere ; hence the 

 earth's atmosphere is not indefinitely divisible, and does not extend 

 to those bodies, and therefore it is thought that its ultimate atoms 

 must be indivisible, and this is regarded as a direct proof of the truth 

 of the atomic theory, or, in other words, of the existence of indivisi- 

 ble atoms or particles. 



(/.) WINDS are produced by the ascent of rarefied air arising from 

 the pressure of colder and heavier air towards the heated place. 

 Thus, as already stated, page 68, are produced the trade winds, 

 monsoons, and land and sea breezes, and the irregular winds. 



(k.) The draught of a chimney is owing to atmospheric pressure; 

 the column of air in the chimney rarefied by heat, is lighter than the 

 adjacent column of colder air, and therefore ascends from the pre- 

 ponderance of the latter. 



(I.) The refractive power of the air is observed in the elevation 

 of ships and other objects near the horizon, and in the effect on the 

 heavenly bodies in the same situation, causing them to emerge sooner 

 when rising, and to linger later when setting. 



(m.) It has been already stated that the higher regions of the at- 

 mosphere are cold ; the temperature in the lower regions, dimin- 

 ishes at the rate of one degree for every three hundred feet. 



2. CHEMICAL PROPERTIES. 



(a.} Air supports combustion, as every one knows. 

 b.) It generates acidity in vinous fluids. 



(c.) It oxidizes some of the metals, at the common temperature, 

 and most of them at ignition. 



* It is calculated, that at 46 miles below the surface, air would have the density 

 of quicksilver. 



t For an excellent analysis of this curious paper, see Murray, 6th Edit. Vol. I, 

 p. 413. 



