994 Mr. Gr. H. Livens on a Theory of the 



In weighing, the weights are placed in the right-hand pan, 

 the rider being at its zero mark. Weights to the nearest 

 gramme (less than the weight of body) are put into the pan 

 i£ the half-gramme rider is used ; the case is closed, and 

 the fractions of a gramme are given by one setting of the 

 rider. 



The sensitiveness of the balance should be so adjusted 

 that the smallest readable change of position of the rider 

 gives the smallest readable change of deflexion. 



Experiment shows that even in a very draughty room 

 currents of air through the slits do not introduce errors 

 unless very delicate measurements are being made. Such 

 currents can be prevented by having a second slit in another 

 piece of metal pivoted so that the cord can pass through the 

 intersection of the two slits. 



The diagram represents a cheap form of balance which has 

 been fitted in the workshop with the modifications described. 



No new principle is involved, but a balance so fitted has 

 been found to give great saving of time and labour in 

 weighing. 



CVI. On a Theory of the Rotational Optical Activity in 

 Isotropic Media. By G. H. Livens*. 



IN some recently published papers f the author, starting 

 from a suggestion originally made by H. A. Lorentz, 

 has given indications towards a new form of the electron 

 theory of the optical rotatory power in isotropic media. The 

 results obtained are in such close agreement with the experi- 

 mental facts that there can hardly be any doubt as to the 

 correctness of the fundamental assumptions on which they 

 are based. The object of the present paper is to give now 

 as complete a statement of the theory as possible, in the hope 

 that it may lead to further experimental investigations of its 

 appropriateness. 



In the modern electromagnetic theory of optics we have 

 always to deal with the electric and magnetic force and the 

 electric and magnetic flux, such that each flux is derived from 

 the other force by the universally valid circuital relations. 

 If we denote the electric and magnetic force vectors by E 

 and H respectively and the corresponding fluxes by D and 



* Communicated by the Author. 



t " On Rotational Optical Activity of Solutions/' Phil. Mag. June 



