572 



METEOEOLOGY. 



the bottom of the bulb being broken off to allow 

 of introducing water into it, when desired, could 

 then be replaced so as to close the bulb again. 



The experiments were duplicate first, with 

 air only in the bulb, then with a little water 

 added. In either case, the bulb was made to 

 dip into a vessel of warm, and the TJ into an- 

 other of cold water ; the temperatures of both 

 these were noted, and also the distances to 

 which the mercury was moved along the tube. 

 As an example of the experiments : the cold 

 water in the second vessel being at 12 C., and 

 the warmer water in the first being from 15.7 

 raised to 41. 8 , the bulb containing air only, 

 the mercury globule advanced along the tube 

 11.47 Paris inches. Water being afterward 

 introduced, and when, by Dalton's theory, even 

 if the vapor resulting had penetrated quite to 

 the mercury, the latter should by the same 

 temperatures have been moved, at most, but 

 j^th farther, it was found on trial that the 

 actual motion produced was nearly doubled ; 

 and now, to secure movement of the mercury 

 over 11.47 Paris inches, it was only requisite 

 to raise the temperature of the bulb from 

 15.7, to 30. 9 C. Now, the calculated increase 

 of the expansive force of the dry air, in the 

 first case, equals .119 of its pressure at the out- 

 set ; and the calculated increase of expansive 

 force in the second case is for the dry air .070, 

 and for the vapor .048, together making .118 

 of the pressure at the outset. An identity 

 very nearly as close as this runs between the 

 two classes of results in all the experiments ; 

 and in view of the fact (established by other 

 means) that, in the cases of added vapor pres- 

 sure, the vapor had not advanced even to the 

 U bend of the tube, it follows accordingly that 

 the vapor of the water, while yet but partially 

 distributed through the enclosed space, is al- 

 ready exerting the full pressure due to its den- 

 sity and temperature. To determine whether 

 the penetration of the vapor to the mercury 

 would produce a difference in the result, the 

 warmth of the water about the bulb was in one 

 instance maintained for a full hour ; but the 

 mercury was not in consequence moved farther. 



Professor Larnont concludes from these ex- 

 periments and other data that Dalton's theory 

 must be erroneous ; that in the atmosphere, the 

 aiivproper presses on the vapor, and the vapor 

 on the air. This, however, expresses only the 

 effect ; and he anticipates being able to show, 

 at some future time, that the humidity in the 

 atmosphere must be regarded as actually ad- 

 hering to the molecules of air ; and that the 

 phenomena admit of a simple explanation by 

 means of a natural hypothesis concerning the 

 expansion of dry and of wet molecules of air. 

 Applying the new theory to the case of the at- 

 mosphere, it must be inferred, since the diffu- 

 sion of vapor in air takes place very slowly, 

 and since, from natural causes, very different 

 quantities of vapor pass into the air at different 

 places, that in regard to the humidity of the 

 air no relations exist that can be, strictly speak- 



ing, conformable to any law. Of course, the 

 currents of air continually occurring will as 

 constantly intermingle masses of air more or 

 less humid ; but this action takes place in no 

 uniform manner. There can thus be no exact 

 relation of dependence between the degrees of 

 humidity of different points in space. But par- 

 ticularly, the idea of an atmosphere of vapor 

 subsisting independently within the general at- 

 mosphere, appears wholly inadmissible ; and the 

 data furnished by the psychrometer can no long- 

 er be regarded in any other light than as expres- 

 sions of local humidity of the places at which 

 they are obtained. "Philos. Mag.," Nov., 1862. 

 Vapor of the Upper Atmosphere. Lieut.-Col. 

 R. Strachey, inalong communication before the 

 Royal Society, and which appears in the journal 

 just quoted (April, 1862), furnishes a second 

 proof of the inadmissibility of Dalton's theory. 

 His position is that previously taken by Bessel, 

 but supported by a wider and more exact sur- 

 vey of facts. An independent vapor atmos- 

 phere, if such exist, must within itself conform 

 to the general laws of pressure of elastic fluids. 

 But the specific gravity of the vapor is less than 

 that of the dry air in the ratio of about .625 to 

 1, or 5 to 8. Consequently, the rate of dimi- 

 nution of pressure on the upper strata of the 

 vapor atmosphere would be much slower than 

 that holding true in respect to the air or general 

 atmosphere ; and, leaving aside any effect of 

 temperature, the height required in the vapor 

 atmosphere to produce a given diminution in 

 density, must be to the corresponding height 

 in the general atmosphere, inversely as the 

 specific gravities of the two, or about as 8 to 5. 

 Thus, the barometric pressure being by an as- 

 cent of about 19,000 ft. reduced one half, to 

 reduce the pressure of the vapor atmosphere 

 in like ratio a height of 19,000 x f = more than 

 30,000 ft. must be reached. Mr. Strachey then 

 gives tables showing in parallel columns the 

 tensions (and hence, the proportionate quanti- 

 ties) of vapor, at different elevations ; first, as 

 calculated from Dalton's theory, and secondly, 

 as actually observed by Dr. Jos. Hooker, in as- 

 cending the Himalayas to upward of 18,000 ft., 

 and by Mr. "Welsh in balloon ascents to a height 

 of 23,000 ft. 



The vapor tension at the earth's surface, as 

 observed, being called 1, and this being neces- 

 sarily the unit or value for the same leA*el by 

 Dalton's theory, then the calculated tensions 

 according to this theory, at heights respectively 

 of 4,000, 8,000, 12,000, 16,000, and 20,000 ft., 

 should be expressed by the fractions .92, .84, 

 .77, .70, and .64 of the vapor at the surface; 

 while the actual tensions found by Dr. Hooker 

 at the heights severally named (the last only 

 being determined by calculation), were as low 

 as .68, .52 .35, .25, and .16 of the vapor at the 

 surface ; and those of Mr. "Welsh for like eleva- 

 tions .77, .45, .30, .18, and .12 of the vapor at 

 the surface. Observations for certain heights 

 made at other points correspond nearly with 

 those here given. (See, also, Mr. Glaisher's 



