Phenomena of the Capillary Electroscope. 



95 



ebonite electrophorus was used as the source of electricity, and in these 

 cases also the mercury moved in the direction of electric discharge. 

 With the horizontal electroscopes (all of which were open at both 

 ends), the mercury only moved at that end at which the current or 

 discharge passed ; but if the current or discharge passed at both ends 

 simultaneously, then the mercury moved at both ends simultaneously, 

 whether the electric flow was from end to end, from both ends to 

 middle, or from middle to both ends (provided it was free to move), 

 and the directions of the motion in the two ends agreed with the 

 above general statements. 



In these various experiments the amount of capillary movement 

 with a given current did not appear to vary greatly with the total 

 bulk of mercury in the entire apparatus. 



The displacement of volume of the mercury being so extremely 

 small, it may be accounted for on the supposition that minute traces 

 of air (not visible by means of an eye-glass) adhere to the sides even 

 of the smallest and most perfectly prepared tubes ; and when by the 

 action of the current or discharge, the meniscus is caused to approach 

 the capillary orifice, these minute portions of air become rarefied. 

 This view is supported by the facts, that traces of air are con- 

 tinually observed in the capillaries, and also that when the appa- 

 ratus was reduced to its simplest form and smallest size, as in ]S"o. 5a, 

 the motion of the meniscus appeared to be somewhat less free. 



From these results, I consider it improbable that the movements 

 are to any large extent attended by a change of volume of the 

 mercury. 



6. Influence of Adhesion, Capillarity, and Surface Tension. 



In a paper " On the Adhesion of Liquids to Mercury " (" Phil. 

 Mag.," vol. 26, 1863), I have stated that "if a drop of Nordhausen 

 sulphuric acid, about one-tenth of an inch in diameter, is carefully 

 placed by means of a glass rod upon the centre of a clean globule of 

 pure mercury, about 80 grs. in weight, it instantly diff uses itself in 

 a thin film over the surface of the metal, and the mercury becomes 

 flattened, and exhibits vertical movements all over its surface ; but if 

 the experiment is made with a strong aqueous solution of ammonia or 

 of caustic potash, no such results occur, the alkaline solution contracts 

 itself into a spherical form, and persistently floats to the side of the 

 mercury without spreading itself over the surface." 



This circumstance, viz., the small adhesion of aqueous ammonia to 

 mercury, is probably connected with another already mentioned (see 

 p. 88), viz., that when the mercury was caused to flow out of the end 

 of the capillary tube into a solution of ammonia, it would only emerge 

 in large drops instead of the usual stream of minute ones. Difference 



