C. GENERAL PHYSICS. I45 



these two states possess in general different physical proper- 

 ties. 6 B, 1873, 1080. _; 



EECENT KESEARCHES IN HYDEAULICS. 



The laws of the motion of water, whether in rivers or seas, 

 liave been very successfully studied by Boussinesq, who has 

 presented a profound memoir on his subject to the Paris 

 Academy. In giving a general review of his studies we 

 may say that Boussinesq, having shown that the formulae 

 and the methods employed by engineers strictly refer to the 

 motion of w^ater in straight channels, then proposes, as liis 

 problem, to examine, in detail, the effects of friction, eddies, 

 and curves in rivers or pipes. He shows how the value of 

 the coefficient of the flow of water depends on these disturb- 

 ing elements, as also on the internal friction between contigu- 

 ous atoms of the flow^ing water. Boussinesq then considers 

 the problems of water flowing with variable motion, in the 

 solution of which he attains much more generality than any 

 previous author, in that he attacks the problem, by making 

 use not of the principle of living force, but by the considera- 

 tion of the theorems of quantity of motion. In the further 

 study of the flow of water in rivers, he finds that when the 

 uniform regimen begins to be established, after a rise, the 

 surface of the fluid is affected by a series of transverse undu- 

 lations havinoj the same dimensions in the direction of the 

 current as the rapidly decreasing height of the water. Pass- 

 ing, then, to the movement of waves in a river, either up or 

 down the current, Boussinesq shows the effect on these of 

 eddies and frictions, and deduces a formula such that if these 

 disturbances be neglected, it is reduced to that of Lagrange 

 and Scott Russell, which has been employed for a long time, 

 although known to be imperfect. After this nearer approxi- 

 mation to the actual problems of nature, the author finally 

 examines the effect of the curvins^ of what he had hitherto 

 supposed to be a straight channel. Other questions, as to 

 the phenomena of initial waves, etc., are successfully treated. 

 6^,1873,943. 



CIILOEINE ACTIVE IN THE DARK. 



Melsens has observed that porous varieties of carbon (coke, 

 for example) will, after purification, absorb nearly their own 



G 



