Lord Rayleigh : Investigations in Capillarity. 327 



with the atmosphere. If a body is rendered inactive by pro- 

 longed standing in cold water; by treatment with alcohol, 

 ether, &c, " qui dissolvent les gaz de Pair, plus abondamment 

 que l'eau "*; or by heating in a flame; it is because by such 

 processes the film of air is removed. One cannot but sym- 

 pathise with Tomlinson f in his repugnance to such an explana- 

 tion; but the position maintained by the latter that activity 

 is due to contamination with grease is also not without its 

 difficulties. 



The question whether contact with air suffices to restore 

 the activity of a piece of glass or metal that has been ren- 

 dered inactive by heat or otherwise, appears to be amenable 

 to experiment, and should not remain an open one. In 1892 

 I had a number of glass tubes prepared of about 1 cm. diameter 

 for experiments in this direction. After a tborough heating 

 in the blowpipe-flame, the ends of the tubes were hermetically 

 sealed. At intervals since that date some of the tubes have 

 been opened and compared with others which had undergone 

 no preparation. Short lengths of rubber provided with 

 pinch-cocks are fitted to the upper ends, by means of which 

 aerated water is easily drawn in from a shallow vessel. Three 

 tubes remaining over from the batch above mentioned were 

 tried a few weeks ago, and establish the conclusion that 

 seven years contact with air fails to restore activity. A similar 

 experiment may be made with iron wires. If these be heated 

 and sealed up in glass tubes, they remain inactive, but expo- 

 sure to the air of the laboratory for a day or two restores 

 activity. 



In opposition to the contention that grease is the primary 

 cause of activity, Gernez brings forward a striking experi- 

 ment from which it appears that a drop of olive-oil itself 

 liberates no gas when introduced with precaution. " Quant 

 au role que jouent les corps gras, il est facile de s'en rendie 

 compter lorsqu'on frotte un corps quelconque entre les doigts 

 legerement graisses, on produit a sa surface une serie d'euii- 

 nences lineaires separees par ies sillons qui correspondent aux 

 lignes de l'epiderme; les cavites forment un reseau de con- 

 duits qui contiennent de Fair, sont difficilement mouilles par 

 l'eau et, par consequent, constituent au sien du liquide une 

 atmosphere, eminemment favorable au degagement des 

 gaz"J. 



It seems to me that Tomlinson was substantially correct in 



* Annates de VEcole Normale, 1875, p. 319. 

 t Phil. Ma#. vol. xlix. p. 305 (1875). 

 1 L. c. p. 846. 



