778 
DR. OLIVER LODGE ON ABERRATION PROBLEMS. 
Air Effect. 
47. Of course, there must be an effect due to the air which is whirled with the disks. 
The index of refraction for air is 1‘00029 for yellow light, and so. 1 — l/g," = ’00058. 
The effect dependent on air amounts, therefore, to of speed of the disks, 
and is smaller than any shift which at present I have been able to observe. 
I should like to push the method far enough to detect the air effect.* 
A great number of other experiments suggest themselves. It maybe objected that 
the disks were too far apart, or that insufficient time was given for the viscosity of 
the ether to assert itself, or that the disks had inadequate mass. This last objection 
IS, perhaps, important, and I am proceeding to cope with it, and incidentally with the 
others, in some new experiments. A positive result could no doubt be obtained by 
rotating frame and observer instead of the disks. 
The apparatus used in the above reseai’ch was constructed by means of generous 
aid volunteered by a private friend, to whom I hereby express my, grateful thanks. 
* [The effect of centrifugal force on the density of the air between the disk.s, and the influence of 
varying density, will be discussed with other matters in a future communication.—July, 1893.] 
