(944) 
first mentioned difficulty was overcome, and with which some 
satisfactory measurements of the magnetic rotation dispersion in 
liquid methyl chloride have been made. 
In this apparatus, shown in fig. 1, the experimental tube D and 
the nicols C are enclosed in a brass jacket A with double walls, 
filled with liquid methyl chloride, insulated from the heat of the coil 
by a layer of wool. The space within the jacket is closed on either 
side by the ebonite caps .V of the previous apparatus, with the 
india-rubber rings O as packing-washers and 6 tightening rods. In 
these caps the glass plates B are fixed with the serew-rings P, and 
thin india-rubber leaf as packing. The other nuts and rings connected 
with them have remained unchanged. 
The circulation of liquid methylehloride through the jacket is 
obtained from the cryogenic laboratory, where a connection with 
the methyl chloride reservoir with its Compression pump can be 
made 5. The liquid is supplied through a high pressure cock /, 
(see fig. 2) while the escaping vapour streams back to the cryogenic 
laboratory through the tubes AA. A float / enables us to know 
at any time whether the jacket is filled. 
The experimental tube D consists of a glass tube of 35 ¢.m. having 
an opening G in the middle and closed by two glass plates 1 m.m. 
thick, fastened to it by means of fish glue. The nicols C, rotating in 
elastic brass rings, are mounted on either side. It is true that now 
there is glass between the nicols, and the unfavourable influence of 
this makes itself felt, however to a much smaller extent, so that 
adjustments can be now made. 
The apparatus is filled through a steel capillary MH, passing through 
an india rubber stopper in an aperture in the jacket and entering 
the testing tube. 
The methyl chloride required to fill it is obtained by distilling the 
commercial article, which has been once distilled already, onee more, 
the vapour passing through a drying tube into a spiral immersed in 
a reservoir of liquid methyl chloride under atmospheric pressure, 
supplied by the same tubes which were used for the liquid in the 
jacket deseribed. 
Liquid methyl chloride flows from this spiral through the steel 
capillary HZ connected with it, into the experimental tube under 
atmospheric pressure and hence having the same temperature as the 
jacket and the space within. The tube // to which a piece of india 
rubber tubing is connected, serves to remove the vapour formed 
1) Comp, Communication N°, 14, These Proceedings, Dec. 1894, 
