VELOCITY OP WHITE AND OP COLOURED LIGHT. 
285 
The mean of these is 2‘03 per cent., giving a result which confirms in a satisfactory 
manner the results arrived at by the other methods. 
April 26 and 27.—After an absence of a month from Kelly we again tested the 
colour effect on April 26 and 27. We used wheels with 250 teeth and with 400 
teeth, bright and smoked, upright and inclined. We ascertained the fact that blue 
light required the greater velocity of rotation to produce equality; but we did not 
make any actual measurements. We were unable to detect the successive phases of 
colour which were observed on February 11. 
By collecting results of all the observations on the effect of colour on velocity we 
shall be able to judge of the general effect:— 
February 11.—The star which was increasing with increase of speed was red; the 
star which was waning with increase of speed was blue. 
The percentage difference of red and white light, two observations, 0*90 and 0*32. 
February 21.—Ruby-red glass and blue copper solution. Speed diminished 
gradually by indiarubber. Eight observations— 
(1) 3*36 (3) 2*40 (5) 5*40 (7) 2*40 
(2) 1*14 (4) 2*88 (6) 2*46 (8) 2*52 
Mean percentage difference =2*82. 
February 23.—Red solution and blue solution. Direct measurements of the change 
of velocity. Two observations at different speeds— 
(1) 1*96 (2) 0*36 
Mean percentage difference =1*16. 
February 24.—The effect seemed to be of the opposite kind to that hitherto 
obtained. 
February 25.—Red and blue solutions. Indiarubber method. Three observations— 
4 
(1) 0*29 (2) 0*43 (3) 0*70 
Mean percentage difference =0*47. 
February 27.—Red and blue solutions. Indiarubber method. Eight observations— 
(1) 1*28 (3) 1*71 (5) 3*14 (7) 1*40 
(2) 1*22 (4) 1*55 (6) 1*10 (8) 0*68 
Mean percentage difference =1*51. 
March 1.—Pure spectrum thrown by bisulphide of carbon prism upon the toothed 
wheel. Blue and red parts of the spectrum used in succession. Indiarubber method. 
Four observations— 
(1) 1*35 (2) 1-56 (3) 0*90 
Mean percentage difference =1*17, 
(4) 0*90 
