exvi Proceedings of the Asiatic Society of Bengal. [N.S., XV, 
viz. that the velocity of light propagation is the same, what- 
ever the frame of reference (whether the source is at rest 
or in motion), and it is then found that the equations of trans- 
formation from #,, y,, z,, t,, to v, y, z, t, are the same as in the 
electron theory of Lorentz and Larmor, and the Fitzgerald-con- 
traction as well as other null-effects are then similarly explained. 
I may cite the simple case of local time which depends on 
the standard time as well as the position of the observer. Of this, 
Kinstein’s conclusion may be held to be a generalisation based 
are ultimately based on an optical method, and a r 
dards depend on the velocity of light. Since, therefore, any 
uncertainty in thi ld introduce a complete uncertainty 
into the entire range of our experience, Einstein’s postulate of 
constant light velocity, which also enters as a constant in 
Lorentz and Larmor’s equations, seems to be a priori justified. 
The justification of a theory is best measured by its power 
to explain outstanding problems, and accordingly an attempt 
has been made to apply the theory of relativity to explain 
several phenomena of this nature. I shall refer to two of these : 
ted with relativity phenomena Since, then, however, he has 
made further researches and he now writes to me to say that 
it is now certain that the red shift on the sun is not even in - 
part due to Einstein effect. 
argued on the other side that a suitable modification of the New- 
tonian theory is competent to yield the same result also, It 
does not appear, in fact, that a final pronouncement on the 
point is as yet possible. 
__It must be admitted, however, that the future is rich 
with possibilities for this theory. If this is so it suggests a 
difficulty, which though serious does not seem to be insur- 
mountable. For it seems to indicate that any two frames of 
reference, are equally valid frames of reference, no matter how 
they are moving relatively to each other provided the unique 
condition as to the constancy of light velocity is satisfied, with 
