1918.] The Fifth Indian Science Congress. exvii 
have been made by English physicists. This can be explained 
rhaps in this way. arge part of the work in modern 
physics for the last 20 vears has been intimately connected 
with the problem of the structure of the atom, and among 
several very powerful methods of attack developed for solving 
the problem, those of radio-activity and X-Rays absorbed the 
attention of the British scientists, in whose hands they have 
yielded such wonderful results. The only literature on magneto- 
optics available in the English language consists of an admir- 
able monograph by Zeeman published in 1912. Since that 
predicting results verified by experiment, suggesting modifica- 
tions in the theory accepted by the mathematicians. No one 
is more indebted to the mathematical genius of Lorentz and 
Voigt than Zeeman himself. 
Instruments of Observation. 
; As for ) : 
interferometers, Lummers’ plates and Michelson’s echelon still 
ain the chief spectroscopic accessories. Rowlands’ con- 
ay grating is yielding its place to Michelson’s plane grating 
recently suggested several methods of producing intense mag- 
hetic fields. One of them consists of adding a magnetising coil 
a Weiss magnet. Another method consists of allowing a 
very large current to circulate round an insulated strip of high 
