TRANSACTIONS OF THE SECTIONS. 31 



slowlj- moving molecules wliich are advancing towards the heated surface ; it thus 

 happens that though the individual kicks against the heated sm-face are increased 

 in strength in consequence of the heating, yet the number of molecules struck is 

 diminished in the same proportion, so that there is equilibrium on the two sides of 

 the disk, even though the temperatures of the faces ai-e imequal. But when the 

 exhaustion is carried to so high a point that the molecules are sufficiently few, and 

 the mean length of path between their successive collisions is comparable with the 

 dimensions of the A-essel, the swiftly moving, rebounding molecules spend their 

 force, in part or in whole, on the sides of the vessel, and the onward crowding, 

 more slowly moving molecules are not kept back as before, so that the number 

 which strike the warmer face approaches to, and in the limit equals, the number 

 ■which strike the back, cooler face, and as the individual impacts are stronger on 

 the warmer than on the cooler face, pressure is produced, causing the warmer face 

 to retreat*. 



Mechanical Theory of the Soaring of Birds. By W. Froxjde, F.E.S. 



On the Passage of Fluids through Capillarij and other Tubes. 

 By Professor F. Guxhrie ayid Dr. F. Gtjthrie. 



0)% the Modification of the Motion of Waves produced by Fluid Friction. 



By Prof. J. PcTESEK. 



On the Forces experienced hy a Lamina immersed vblirpiely in a Fluid /Stream. 



By Lord Eayletgh, F.B.S.f 



On the Besistanci encountered by Vortex Rings, and the llelation between the 

 Vortex Ring and Stream-lines of a Dish. By Prof. Osborne Eetnolds. 



Description of the Batliometsr. By Dr. C. W. Siemens, F.B.8. 



On the Amplitude of Waves of Light and Heat. 

 By G. Johnstone Stonet, F.R.S. 



On Acoustic Analogues to Motions in the Molecules of Oases. 

 By G. Johnstone Stoney, F.R.S. 



Experimental Illustration of the Origin of Windings of Rivers in Alluvial 

 Plains. By Professor James Thomson, LL.B., D.Se. 



The author referred to a communication which he had made to the Royal Society 

 in the month of May last J, in which he had given a new theory of the flow of 

 water round bends in rivers and round bends in pipes, and had explained the 

 reason why, in alluvial plains, the bends of rivers go on increasing hy the wearing 

 away of the outer bank, and the deposition of mud, sand, and gravel on the inner 



* For further researches on this subject, see papers read before the Royal Society, 

 November 16, 1876, aud on April 26, 1877. 



t Printed in extenso in the Phil. Mag. 1876, ii. p. 430. 

 X Proc. Eoy. Soc. vol. xxv. p. 5. 



