234 Messrs. Rodger and Watson. Magnetic [June 20, 



Curve (1) 'gives the values of the refractive indices at temperatures 

 between and 9, as determined by the experiments, of which an 

 account has been given in this paper ; and curve (2) the densities 

 of water at the same temperatures as given in Lupton's ' Numerical 

 Tables' (p. 28). 



These curves show clearly that no formula representing the 

 variation of the refractive index of water with the temperature, as a 

 function of the density only, can be a complete expression of the 

 facts of the case. 



IV. "On the Magnetic Rotation of the Plane of Polarisation of 

 Light in Liquids. Part I. Carbon Bisulphide and Water." 

 By J. W. RODGER, Assoc.R.C.S., Demonstrator of Chemistry, 

 and W. WATSON, B.Sc., Assoc.R.C.S.. Demonstrator of 

 Physics, Royal College of Science, London. Commu- 

 nicated by Professor A. W. RUCKER, F.R.S. Received 

 June 1, 1895. 



(Abstract.) 



The aim of this investigation is the determination in absolute 

 measure of the magnetic rotation of liquids at different temperatures, 

 the effect of the chemical nature of the liquid on this property, and 

 its correlation with other physical properties. 



The present communication contains a description of the apparatus 

 and method of experiment, and the results obtained with the standard 

 liquids, carbon bisulphide and water, for sodium light, in a magnetic 

 field of constant intensity, and at different temperatures between 

 and the ordinary boiling point. 



The magnetic field was produced by means of a helix consisting of 

 two separate coils, either of which, if desired, could be used separately. 

 During the process of winding, the dimensions of each layer were 

 carefully determined, and every precaution was taken to ensure good 

 insulation. 



The liquid under examination was contained in a glass tube closed 

 by very thin glass plates. This tube was surrounded by a brass 

 jacket, which passed through the coils. Observations could be made 

 at different temperatures, and the temperature could be kept con- 

 stant while making a set of readings by causing water, or the vapour 

 of liquids boiling under different pressures, to circulate through the 

 jacket. 



Special pains were taken to obtain monochromatic light, with the 

 result that in the case of carbon bisulphide, where the double rotation 

 amounted to 40, there was no trace of coloration. 



