1921.] The Kighth Indian Science Congress. exix 
ee unit ; sae ~ tangent at R meet the curve in P and the tangent 
eet the curve in a Then it is sibs that (1) P diseased to the 
Null I algebra Mae: ) Ge rresponds to the primitive — (3) the lines 
PR represent the factors of the Resultant of f and D 
A new y method of pune ake is ee W. A. * ENKINS. 
solenoid then gives a measurement of ‘‘H.”’ In the second method the 
solenoid is set accurately ae to the earth’s igre An external bar 
magnet in the Tangent ‘‘B” position of Gau thén deflects the sus- 
is now 
magnet. The deflection must of course be appro tely 45°, 
the ane metho dq the measurement of the cieees print ee with the 
solenoid es a bier of 
‘he accuracy oF the method is discussed and it is shown that : is as 
accurate as the Kew Magnetometér method, and easier to carry ou 
On the colours of pian seg and other Optical Investi- 
gations.—By C. 
1. In this paper, a ae account was given of anumber of optical 
investigations pear | Saehige out by the author in association with his 
ach 
research scholar case, observations were described which 
= howed that ely theory of the phenomenon hitherto accepted is either 
sige ete or ines “ne e, and a new treatment was suggested to explain 
ie of Mixed plates.—This well-known phenomenon, 
which dee studied homas Young and Brewster, has in more rece cent 
i e . Woo 
iscus and 
hence scatter light in an unsymmetr ical manner. The quantitative 
development of Pe theory gives results in complete agreement with 
observation. 
3. The Colours of Breathed-on Glass Plates.—This beautiful optical 
phenomenon was explained by Karl Exner and by Donle, who however 
: : a 
The real element of oe genase ‘whiah gives rise to the observed colours 
is neither in the size of the water-drops nor in their arrangment, but in 
the angle of contact between liquid an and plate ae 
4, The Colours of Ammonium Chloride films.—This case is in several 
respects analogous to the one just menti ioned. 
