Mr. F. Guthrie on Approach caused by Vibration, 309 



adiabatic waves. He also claims as new the method of investigation 

 by the aid of mass -velocity and mass- coordinates, which he alleges to 

 possess great advantages in point of simplicity. 



"On Approach caused by Vibration." By Frederick Guthrie. 



The author observes that when a vibrating tuning-fork is held near 

 to a piece of cardboard, the latter has a tendency to approach the fork. 

 Starting from this experiment, a series of experiments are described 

 having for their object the determination of the cause and conditions 

 of the fundamental observed fact. 



It is shown that no sensible permanent air-currents, having their 

 source at the fork's surface, are established — and hence that the ap- 

 proach of the card to the fork is not due to the expansion of such 

 currents, as in M. Clement's experiment. 



The modifications are examined which Mr. Faraday's surface- 

 whirlwinds on a vibrating tuning-fork undergo when the fork vibrates 

 in the neighbourhood of a sensibly rigid plane. 



It is shown that a delicately suspended card approaches the fork 

 when either of the three essential faces of the fork is presented to the 

 card, and that the approach takes place from distances far exceeding 

 the range of Mr. Faraday's air-current. That the action between the 

 card and fork is mutual is shown by suspending the latter. Also 

 one vibrating fork tends to approach another in whatever sense their 

 planes of vibration may be towards one another. 



The mean tension of the air surrounding a vibrating fork is ex- 

 amined by enclosing one limb of the fork in a glass tube. It ap- 

 pears that the vibrating fork displaces air. 



The question whether the equilibrium between two equal and op- 

 posite forces acting on a body is disturbed by submitting one of the 

 forces to successive, rapid, equal and opposite alterations in quantity, 

 is answered in the negative by an experiment which shows that the 

 equilibrium of a Cartesian diver is not disturbed by submitting the 

 water in which it floats to vibration. 



Various modifications are introduced into the nature of the sur- 

 face which receives the vibrations, such as making it a narrow cylin- 

 der with one end closed, making it of cotton-wool, &c. It is found 

 that in all cases the suspended body approaches the vibrating one. 



The author concludes that the effect of apparent attraction is due 

 to atmospheric pressure, and that this pressure is due to undulatory 

 dispersion. It is suggested that the dispersion of the vibrations 

 which constitute radiant heat may cause bodies to approach, being 

 pushed not pulled. 



February 24, 1870. — Lieut.-General Sir Edward Sabine, K.C.B., 

 President, in the Chair. 



The following communication was read : — 



" On the successive Action of Sodium and Iodide of Ethyle upon 

 Acetic Ether." By E. Frankland, F.R.S., and B. F. Duppa, Esq., 

 F.R.S. 



In a paper by Mr. J. Alfred Wanklyn, bearing the above title, 



