On the Distribution of Aqueous Vapour in the Atmosphere, 153 



Table I. — Comparison of Tensions of t Daltons Hypothesis with 

 those actually observed. 



Height 



above the 



earth's 



surface 



Barometric 

 ircssure of 

 the entire 



Calculated ten- 

 sions in atmo- 

 sphere of aqueous 

 vapour alone, that 



Ratio of tensions to surface tension actually 

 observed. 



By Dr. Hooker 



By Mr. Welsh 



At Dodabetta & 



in feet. 



sphere. 



at the earth's sur- 



on the 



in four 



Mahabaleshwar 



face being l'O. 



Himalaya. 



balloon ascents. 



(fide Col. Sykes). 







in 



30-0 



in. 



1-00 



1-00 



1-00 





2,000 



28-0 



•96 



•82 



•88 





4,000 



261 



•92 



•68 



•77 



•67 



6,000 



24-3 



•88 



•62 



•58 





8,000 



22-6 



•84 



'52 



•45 



•47 



10,000 



21-0 



•80 



•42 



•35 





12,000 



10-5 



•77 



•35 



•30 





14,000 



18-0 



•73 



•29 



•19 





16,000 



16-6 



•70 



•25 



•18 





18,000 



15-3 



•67 



•20 



•16 





20,000 



141 



•64 



•16 



•12 





The facts, as indicated by the long series of observations, of which 

 the Table contains an abstract, are altogether in accordance with the 

 results of my own observations ; but I have thought it better to rest 

 my conclusions on the facts observed by others. Further, the discre- 

 pancy between the observations and the hypothesis is so great, and 

 so constant with reference to all the localities, the Himalaya, En- 

 gland, and the mountains of the south of India, while the observa- 

 tions are themselves so thoroughly consistent, that the conclusion is 

 inevitable that the hypothesis is untenable. 



A similar conclusion as to the entire incompatibility of the hypo- 

 thesis of a separate vapour atmosphere with the facts, may be drawn 

 quite independently of any observation of tensions, from a mere con- 

 sideration of the known laws of the diminution of temperature as we 

 ascend. An argument, something to this effect, will be found in 

 Bessel's paper on Barometric Heights *; but its form being too ma- 

 thematical to be generally intelligible, I shall endeavour to place the 

 matter in a rather more popular point of view. 



Let us suppose, then, that we are at a place at the sea-level where 

 the temperature of the air is 80°, the tension of vapour being "80, 

 which would make the dew-point 72°*5 — a case that must be of con- 

 stant occurrence. If, now, we rose gradually above the earth's sur- 

 face, the temperature of the air would be reduced at the known rate 

 of about 3° for 1000 feet ; while the tensions of vapour, and the cor- 

 responding dew-points, calculated upon the hypothesis of an atmo- 

 sphere of vapour pressing upon itself, would be as follows : — 



ft - 



At . . Tension -80 . . Dew-point 72*5 .. Air 80*0 



1000 .. „ -78 .. „ 71-8 .. „ 77-0 



2000 .. „ '77 .. „ 71-2 .. „ 74-0 



3000 .. „ '75 .. „ 70-5 .. „ 71'0 



4000 .. „ 74 .. „ 69-9 .. „ 68'0 



* Astronomische Nachrichten, Nos. 356, 357 ; aud Taylor's Scientific Memoirs, 

 vol. ii. p. 517. 



