Intelligence and Miscellaneous Articles. 505 



usually as loss of heat when substances of any kind are compressed, 

 when liquids " adhere " to solids (as in the above experiments), 

 and when substances chemically " combine ; " it is also shown, 

 though in a less simple form, when bodies approach each other by 

 electric and magnetic " attraction." Conversely, when a gas is 

 rarefied by mechanical means, it gains heat by absorption ; simi- 

 larly, when a film of air adhering to a solid is displaced by a liquid, 

 and when the molecules of a solid or a liquid are separated farther 

 asunder by a solution in a liquid without chemical union, or by 

 dilution of its solution, heat is usually absorbed. 



Although in every one of the 98 experiments of the above 

 research heat was evolved and lost, in about half of the 58 trials 

 with silica the dissolved substance appeared to absorb heat by 

 contact with the powder. These apparent exceptions were prob- 

 ably due to the amount of heat absorbed by the receding film of 

 air being greater than that evolved by the approach and contact of 

 the dissolved substances, and thus those cases were made to appear 

 inconsistent with the above general statement. Similarly, instances 

 of electric and magnetic "■repulsion" are probably only apparent 

 exceptions to that statement, the real phenomena being obscured 

 by the attendant circumstances. 



As in all these various cases, w r hether of " adhesion " of films of 

 air, water, or dissolved substance to solids, of chemical union, or 

 of electric and magnetic attraction, the only factors of the mecha- 

 nical energy of the molecules are mass and velocity, and as in every 

 instance the mass of neither of the acting substances is perceptibly 

 altered, the loss of mechanical energy of bodies by mutual approach 

 and contact, and the gain by mutual recession, must consist 

 entirely of velocity. It is well known that a solid when dissolved 

 in a liquid behaves like a gas, and as the molecules of a gas " move 

 faster the better the exhaustion" (Crookes, Phil. Trans. Roy. Soc. 

 1879, p. 160), so do those of a liquid by being separated by dilu- 

 tion ; this increase of molecular velocity by dilution is also shown 

 by an increase of electromotive force (see Proc. Birm. Phil. Soc. 

 vol. viii. pp. 63-138). 



As these supplementary remarks appear to afford a much wider 

 and more complete theoretical explanation of the phenomena 

 observed with silica &c. than that offered in the original communi- 

 cation, I venture to submit them for consideration. 



i 



POLARIZATION OF NON-DIFFRACTED INFRA-RED RADIATION 

 BY WIRE GRATINGS. BY H. DU BOIS AND H. RUBENS. 



The results of this investigation, a preliminary account of which 

 was given at the Edinburgh B. A. Meeting (1892), may be sum- 

 marized as follows : — 



Gratings were finally made of metal wire down to a diameter of 

 2*5 mem. (" millicentimetre "=0*001 cm.), the interspaces between 



Phil. Mag. S. 5. Vol. 37. No. 228. May 1894. 2 M 



