450 
CAPTAIN ABNEY AND MAJOR-GENERAL RESTING 
It will be remembered that more light was admitted to the prisms with the turbid 
than with the clear water; y was taken to represent the ratio, and the formula 
was applied to each of the above results, which gave eight equations 
containing x and y. By the method of least squares two normal equations were 
formed, from which the values x— *146, y=3'72 were obtained. From independent 
measurements of the apertures of the slit it was believed that the ratio was 3‘8. 
The following table gives the ratios of incident and transmitted light as obtained 
by observation and calculation from Lord PtAYLEioii’s formula. 
X. 
Observed ratio. 
! 
Calculated ratio. 
6448 
16-0 
16-05 
6374 
15-3 
15-4 
6218 
141 
14-05 
6061 
12-2 
12-6 
5900 
111 
11-2 
5589 
8-7 
8-37 
5459 
7-2 
7-22 
5179 
5-0 
4-90 
4602 
3-87 
3-92 
Fig. 8, Plate 25, gives the theoretical carve and the positions of the observed ratios. 
On another occasion, with a different degree of turbidity, the values obtained were 
X'=- '101, y= 2*28 ; from observation y=2*31. 
X. 
Observed ratio. 
Calculated ratio. 
6448 
13T 
12-7 
6374 
12T 
12-35 
6210 
11-85 
11-60 
5900 
10-0 
9-9 
5589 
8-25 
8-1 
5459 
7-4 
7-3 
5180 
5-6 
5-6 
4602 
4-8 
4-8 
Other results of the same character were obtained, but it is unnecessary to give 
them. The values observed and calculated seem in every case to confirm the theo¬ 
retical deductions made by Lord Rayleigh. 
A comparison of the curves, fig. 9, Plate 25, of the absorbed and unabsorbed lights 
will show the modifications which are effected in the spectrum by passing the beam of 
light through a turbid medium. That the waves of shorter length are more absorbed 
than the longer is clear, from the fact that the position of maximum intensity is 
shifted towards the red end of the spectrum. It will be observed that the clear 
water and glass ends of the trough even have somewhat affected the spectrum, for 
there is less convexity in the curve on both sides of the maximum than in the normal 
