exiv Proceedings of the Asiatic Society of Bengal. [N.S., XV. 
The question of aberration raises difficulties of another 
kind. 
When star places were accurately observed, Bradley found 
that they all appeared to describe small ellipses parallel to the 
ecliptic and to complete a cycle in a year. It was, therefore, 
a priori, evident that the observed motion was only apparent 
and must be due to the motion of the observer, carried by the 
earth in its motion round the sun. 
On the Undulatory theory, however, the explanation 
naturally presented a difficulty, as the operation of the medium 
ad necessarily to be taken into account. An explanation 
he effect in Fizeau’s experiments, depending as it did on 
the velocity of the medium (water), gave no information as to 
the velocity of the earth. (Relative to the constant ethereal 
, if any, will depend on the square of 
earth’s velocity, relative to the ether. This is the principle of 
Michelson and Morley’s celebrated experiments, but no such 
effect has actually been observed. Th s, the conclusion is 
either that the ether of space is moving with the velocity of 
the earth, which is evidently untenable, or that there is some 
compensating cause which leads to the null-effect observed. 
