1869.] On Approach caused by Vibration. 93 



baryta with baryta- water, and was identical with Frankland and Duppa's 

 liquid B. 



By the action of liquid A upon ethylate of sodium Geuther has recently 



shown that butyric ether is produced. Geuther's reaction I write thus : — 



Acetate of ethylene- 



sodium. Butyric ether. 



A. C 8 H u 0 3 + C a H 5 NaO = NaC 2 H 4 , C 2 H 3 0 2 + C 6 H 12 0 2 . 

 Finally, I predict that liquid B will give 



Caproic ether. 



B. C 10 H 1R 0 3 + C a H 5 NaO = NaC 2 H 4 C 2 H 3 0 2 + C 8 H ie 0 2 . 



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

 Communicated by Prof. G. G. Stokes, Sec. R. S. Received 

 August 26, 1869. 



(Abstract.) 



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. Start- 

 ing from this experiment, a series of experiments is described having for 

 their object the determination of the cause and conditions of the funda- 

 mental 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 approach 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 neighbour- 

 hood 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 examined by 

 enclosing one limb of the fork in a glass tube. It appears that the 

 vibrating fork displaces air. 



The question whether the equilibrium between two equal and opposite 

 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 surface 



