368 Professor Lamont's New Theory of Atmospheric Vapour. 



adopted distinctions which now-a-days would hardly be admis- 

 sible as indicative of varieties. 



These, then, are the more prominent characters of this 

 remarkable and beautiful genus of Hydrozoa. They have been 

 given somewhat in detail, with a view to incite " those who go 

 down into the sea in ships'' to extend our knowledge ; and to 

 prove that, at all times and under nearly all circumstances, the 

 voyager may find ample food for the mind, and a far from 

 exhaustible field for the instruction of his fellows. 



PROFESSOR LAMONT'S NEW THEORY OF ATMOS- 

 PHERIC VAPOUR. 



BY ALEXANDER S. HEESCHEL, B.A. 



The experiments of Dr. Dalton on the pressure of vapour 

 rising from the surface of water at different temperatures, in 

 free space and in space enclosing air, led to conclusions which 

 have since been received by the compilers of meteorological 

 tables, but which are questioned by M. Lamont, and shown by 

 his experiments to be in some degree fallacious. The vapour of 

 boiling water, or of water at 100 s 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 bubbles which, 

 rise to the surface of water boiling in an open vessel enclose 

 within their pellicle a vapour 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 experiments of Dalton proved that the vapour so enclosed 

 was lighter than the air surrounding, in very nearly the propor- 

 tion of 2 to 3. It follows, by Mariotte's law of equable expan- 

 sion of gases or vapours by heat, that such vapour and such. 

 air exposed to any superior equal temperature, will have to 

 each other the same proportion, in density, of 2 to 3 ; but a 

 further deduction from the experiments of Dalton is this, that 

 water boiled in a partially exhausted receiver of air, will give 

 rise to bubbles which enclose a vapour having equally a pro- 

 portion in density of 2 to 3 to the adjacent air. In short, the 

 vapour of water and common air, wherever these subsist at a 

 common temperature and pressure, are always in the proportion 

 in density of 2 to 3 one to the other. We here 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 



