C. GENERAL PHYSICS. 141 



ON THE THEORY OF THE FLOW OF WATER OR GAS. 



The important work of Boussinesq, entitled " An Essay- 

 on the Theory of Currents of Water," which will be printed 

 by the Academy of Sciences of Paris in the twenty-third 

 volume of its foreign memoirs, has received some interesting 

 additions from its author, among which is one that treats on 

 the transpiration of gases, which interesting subject is known 

 to us at present only through the observations of Grohan, 

 Exner, and others, but whose results are explained by the 

 mechanical theories of Boussinesq. Other additions are 

 those that relate to the uniform regimen of flowing water, 

 and especially, the third addition, that which serves to com- 

 plete the theory of vertical waves, in which the author cal- 

 culates the loss of dynamic energy that the waves experi- 

 ence as a consequence of the mutual friction of the layers 

 of liquid as well as the friction against the containing walls. 

 6 B, LXXXL, 466. 



HYDRAULIC INVESTIGATIONS IN INDIA. 



A very extensive series of experiments by Captain Allen 

 Cunningham on the flow of water in rivers and canals is pub- 

 lished as an extra to the professional papers on Indian engi- 

 neering. After noticing the results derived from Humphrey 

 and Abbott's study of the Mississippi, D'Arcey and Bazeir's 

 studies in France, and Redy's studies on the Paraguay, Uru- 

 guay, and La Plata, he states that the primary object in his 

 own investigations lias been to test the applicability of the re- 

 sults of the American and French experiments to large bodies 

 of water in regular channels. 



Among the conclusions to which his own observations have 

 led him are the unsteadiness in the motion of a large body 

 of water, even in a uniform channel of great length ; the ve- 

 locity at any point varying considerably from one instant to 

 tlie next, although the average velocity is sensibly constant. 

 The curve representing the surface velocity of a current of 

 water is strikingly regular, and is symmetrical with reference 

 to the mid-channel, while its form depends upon the figure 

 of the cross-section. In a very wide channel it has a flat 

 curve. In a rectangular section in masonry it is approxi- 

 mately a quartic ellipse. The surface velocity near the mar- 



