730 Professor Dewar [Jan. 18, 



WEEKLY EVENING MEETING, 



Friday, January 18, 1901. 



His Grace the Duke of Northumberland, E.G. D.C.L. F.E.S. 

 President, in the Chair. 



Professor Dewar, M.A. LL.D. D.Sc. F.E.S. M.B.I. 



Gases at the Beginning and End of the Century. 

 (Abstract.)! 



It is interesting to review in broad outline the century's progress in 

 some limited field of research. The subject of the Gases in its 

 widest sense is too large a province to cover in a single discourse, 

 but if the sketch is confined more especially to the growth of our 

 knowledge of the change of state in gases, then the compass of the 

 review becomes restricted to practicable dimensions. 



At the beginning of the century the doctrines put forth in 

 Lavoisier's ' Elements of Chemistry,' held overwhelming sway. 

 The various states of matter were explained as arising from variations 

 in the amount of caloric with which the body was penetrated. The 

 term caloric must be interpreted as meaning the repulsive cause, 

 whatever that may be, which separates the particles of matter from 

 each other. According as the repulsive power is equal to, stronger, 

 or weaker than, the attraction of the particles the substance became 

 liquid, gaseous or solid. As a general principle it was assumed that 

 every body in nature was susceptible of taking on solid, liquid or 

 aeriform states. 



The elastic aeriform fluids were now characterised for the first 

 time under the generic term gases. A clear distinction was, how- 

 ever, drawn between the caloric which might be said to act like 

 a solvent and the substance or base of the gas with which it was 

 combined. 



The particles of bodies, according to Lavoisier's view, do not 

 make contact with each other, the intervals between them varying 

 according to the figures and magnitude and the existing proportion 

 between their inherent attraction and the repulsive force exerted in 

 them by the caloric. The presentation of caloric, sometimes as a 

 real material or very subtile fluid, did not prevent Lavoisier from 

 generalising with profound sagacity on the fundamental similarity of 

 all known gases. Thus, some thirty years before the definite liquefac- 

 tion of any gas at that time regarded as permanent, in speculating on 

 what would occur provided the earth were suddenly transported into 

 a very cold region, he said, " In this case, the air, or at least some of 

 the aeriform fluids which now compose the mass of our atmosphere, 



