1894.] on Scientific tfses of Liquid Air. 399 



gas under observation is easily ascertained, together with the weight 

 of mercury added. In this way the latent heat of liquid oxygen at 

 its boiling point is about 80 units, and the mean specific heat 

 between - 198° and - 182° is 0-39. 



Seeing that the most powerful chemical affinities are in abey 

 ance at very low temperatures, it is a matter of great interest 

 to ascertain what change comes over the physical force we name 

 cohesion. Here we are dealing with the molecular forces which 

 are effective in uniting together the particles of solid bodies, in 

 contrast to the force we name chemical attraction, which exists most 

 characteristically between dissimilar molecules. Both are alike in 

 this respect, that they are insensible at sensible distances. If we 

 accept the theory of matter which regards finite heterogeneousness of 

 the most homogeneous bodies as proved, then Lord Kelvin has shown 

 that gravitation alone would account for the so called cohesive forces. 

 Thus, he says (' Popular Lectures,' vol. i, page GO) : " But if we take 

 into account the heterogeneous distribution of density essential to 

 any molecular theory of matter, we readily see that it alone is sufficient 

 to intensify the force of gravitation between two bodies placed ex- 

 tremely close to one another, or between two parts of one body, and 

 therefore that cohesion may be accounted for, without assuming any 

 other force than that of gravitation, or any other law than the 

 Newtonian." Another view of the cohesive forces is taken by Mr. S. 

 Tolver Preston, in his work entitled ' Physics of the Ether,' page 64. 

 He says, " The phenomena of ' cohesion,' ' chemical union,' &c, or 

 the general phenomena of the aggregation of molecules, being de- 

 pendent on the molecular vibrations as a physical cause, it would 

 therefore be reasonable to conclude that variation of vibrating 

 energy (variation of ' temperature ') would have a most marked 

 influence on these phenomena, as is found to be the fact. Further, 

 since when a physical cause ceases to exist the effect also ceases, it 

 follows that at the absolute zero of temperature (absence of vibrat- 

 ing energy) the general phenomena of 'cohesion,' including the 

 aggregation of molecules in chemical union, would cease to exist," 

 If this theory is pressed so as to include the gaseous state, then at 

 the temperature of — 274° G. we may imagine the particles reduced 

 to an incoherent layer of dust or powder. The experimental facts do 

 not, however, warrant this conclusion, seeing that at the lowest 

 temperature reached, which is about —210° C, air remains a trans- 

 parent jelly. That a low temperature causes profound changes in 

 the elastic constants of a metallic body is most easily shown by placing 

 a rod of fusible metal in liquid air, and comparing the deflection 

 produced by a weight when the rod is supported at one or both ends 

 before and after cooling. 



The Young modulus is increased to between four and five times its 

 amount at ordinary temperature?. In the same way, the rigidity 

 modulus can be shown to be greatly changed by cooling a spiral 

 spring made of fusible metal wire. Such a spring at the ordinary 

 temperature is quickly drawn out into a straight wire, by attempting 



