Fig. 2. 



372 Lord Rayleigh on Experiments 



The Lowering of Tension by the Condensation of Ether 

 Vapour. 



The suspension of water in an inverted 

 tube of small bore is familiar to all. The 

 limit of diameter was investigated some years 

 ago by Duprez *. A glass tube, such as that 

 shown in fig. 2, is ground true at the lower 

 end, and at the upper end is connected to an 

 india-rubber tube provided with a pinch-cock. 

 Water is sucked up from a vessel of moderate 

 size, the rubber is nipped, and by a quick 

 motion the tube and the vessel are separated, 

 preferably by a downward movement of the 

 latter. In this way of working Duprez found 

 that the liquid might remain suspended in 

 tubes of diameter up to 16 millim., and with 

 the aid of a sliding plate up to 19*85 millim. 

 The theory is given in Maxwell's article in 

 the Encyclopaedia Britannica (" On Capillary 

 Action"). For lecture purposes it is well 

 not to attempt too much. The tube employed 

 by me had an internal diameter of 14J millim., 

 and there was no difficulty in obtaining sus- 

 pension. The experiment on the effect of 

 ether-vapour was then as follows : — The inverted tube, with 

 its suspended water, being held in a clamp, a beaker con- 

 taining a few drops of ether was brought up from below 

 until the free surface of the water was in contact with ether 

 vapour. The lowering of tension, which follows the con- 

 densation of vapour, is then strikingly shown by the sudden 

 precipitation of the water. 



Breath Figures and their Projection. 



These figures are perhaps most readily prepared upon the 

 plan described in Riess's c Electricity.' The carefully cleaned 

 glass plate upon which the image is to be received is placed 

 upon a flat metallic slab, and upon it again rests the coin to be 

 copied, for example, a shilling. The two conductors form the 

 coatings of a Leyden jar, and are connected by wires to the dis- 

 charging terminals of a large Wimshurst machine, the latter 

 being set so as to give sparks about J inch long. In my ex- 

 periments about 20 turns of the handle were found sufficient 

 to impress the latent image. 



* " Sur un cas particulier de l'equilibre des liquides," Bruxelles, Acad. 

 Set. Mem. xxvi. 1851 : xxviii. 1854. 



