110 Mr. W. N. Fenninger on the 



proved that the Hall coefficient in pure mercury and in 

 bismuth amalgams is not greater than 0*00004 c.G.s. electro- 

 magnetic unit, the smallest value which he could detect. An 

 experimental difficulty in the case of liquids, and the chief 

 difficulty if the liquid is metallic, arises from the Lippman 

 effect — the deformation of the liquid film produced by the 

 electromagnetic forces unless the containing vessel is entirely 

 filled. Amerio succeeded in overcoming this difficulty by 

 giving a suitable shape to the containing vessel in one set of 

 experiments, and by combining the observations made in his 

 other experiments in a certain manner to be described 

 below. 



The importance of the subject in the theory of metallic 

 conduction has made it seem advisable to attack the problem 

 of the Hall effect in liquid mercury anew with apparatus 

 permitting of greater precision than that attained by previous 

 experimenters, and to investigate as well the Hall effect in 

 solid mercury, on which no observations appear to have been 

 published. 



The general experimental arrangement was that ordinarily 

 used in studying the Hall effect in metals by the method of 

 direct deflexions. Several ways of holding the mercury 

 were tried. In the final work it was confined between two 

 thin glass plates which were separated by strips of ebonite, 

 and cemented together, mercury tight, by water-glass. The 

 dimensions of the last sheet of mercury upon which work 

 was done in the liquid condition was 5x2 x 0*090 cm. The 

 cavity could be exhausted, or pressure applied, by means of 

 glass tubes connecting with the cavity. Platinum wires 

 were used for both primary and Hall electrodes. The latter 

 were connected directly to a Broca galvanometer, which 

 with its leads had a resistance of about 3*2 ohms. Extra- 

 neous electromotive forces were compensated by a potentio- 

 meter arrangement. The magnetic field was found to be 

 uniform within about 1 per cent, over the region containing 

 the mercury sheet. In the experiments on solid mercury 

 freezing was effected by solid carbon dioxide and ether. 



As is usual, readings were taken in sets of four, as 

 follows : — 



1. Field direct, primary current direct : call the deflexion A. 



2. ., „ „ „ reversed „ „ „ B. 



3. „ reversed „ „ „ „ „ „ C. 



4. „ „ „ „ direct „ „ „ D. 



Now, as Amerio states, at least three effects, superposed 

 upon one another, can give rise to the deflexions : viz., one 



