144 ANNUAL OP SCIENTIFIC DISCOVERY. 



conclusion that the height so attained is to be regarded as the limit of 

 what man can ever expect to reach (or reach with safety), which 

 seems to be Mr. Glaisher's opinion ; and I would throw out the sug- 

 gestion, that were the aeronaut provided with a vessel containing a 

 very moderate number of cubic feet of oxygen gas condensed under 

 a pressure of four or five atmospheres, with the means of letting it 

 out, in small quantities at a time, into a breathing-bag from which he 

 might inhale the pure element at perfect ease, all danger of asphyxia 

 would be avoided, and a mtii'h greater altitude safely attained ; while 

 his strength might possibly be sustained by a supply of that wonder- 

 ful stimulant, the Peruvian coca leaf. As the proportion of oxygen 

 in ordinary atmospheric air is no more than one-fifth of the total vol- 

 ume, and as no inconvenience is experienced in breathing air of half 

 the ordinary density, it is evident that a sufficiency of oxygen to sus- 

 tain the full vital power would be thus obtained under a barometric 

 pressure of three inches of mercury, or one-tenth of that at the sur- 

 face of the earth, which would correspond to a height of about 60,700 

 feet, or 11-| miles, calculating on a decrement of temperature of 10 

 Fahr. per mile, and a temperature of 60 at the earth's surface." 



LAMONT'S NEW THEORY OF ATMOSPHERIC VAPOR. BY ALEXAN- 

 DER S. HERSCHEL, B. A. 



The experiments of Dr. Dalton on the pressure of vapor rising 

 from the surface of water at different temperatures, in free space and 

 in space enclosing air, led to conclusions which have since been re- 

 ceived by the compilers of meteorological tables, but which are ques- 

 tioned by M. Lament, and shown, by his experiments to be in some 

 degree fallacious. The vapor of boiling water, or of water at 100 

 Centigrade, is familiarly known by the vibrations of the lid of a kettle, 

 and by the formation of bubbles upon the surface of the heated 

 water, to have the pressure of the incumbent atmosphere. The bub- 

 bles which rise to the surface of water boiling in an open vessel 

 enclose within their pellicle a vapor whose tension or elastic force 

 is exactly equal to that of the equally heated air which surrounds 

 their envelope, and burst so soon as the quantity enclosed exceeds a 

 capacity proportioned to the thickness of the film. The experi- 

 ments of Dalton proved that the vapor so enclosed was lighter than 

 the air surrounding, in very nearly the proportion of two to three. 

 It follows, by Mariotte's law of equable expansion of gases or 

 vapors by heat, that such vapor and such air exposed to any superior 

 equal temperature will have to each other the same proportion, in 

 density, of two to three ; but a further deduction from the experi- 

 ments of Dalton is this, that water boiled in a partially exhausted 

 receiver of air will give rise to bubbles which enclose a vapor having 

 equally a proportion in density of two to three to the adjacent air. 

 In short, the vapor of water and common air, wherever these subsist 

 at a common temperature and pressure, are always in the proportion 

 in density of two to three one to the other. We hero consider the 

 case of water boiling in air. The pressure of the incumbent air 

 being in this case the exact measure of the elastic force or tension of 

 the vapor emitted by the water at boiling temperature, a table is 



