ON COLOUR PHOTOMETRY. 
431 
Normal Luminosity Curve. 
Scale reading. 
Intensity. 
Scale reading. 
Intensity. 
60-0 
•35 
48-9 
80-0 
59 - 25 
•43 
48-7 
86-5 
58-31 
•54 
48-3 
91-0 
58-0 
•60 
47-8 
97-0 
57-4 
•70 
47-5 
99-0 
56-4 
1-2 
47-1 
100-0 
56-1 
1-3 
46-9 
100-0 
55-8 
1-4 
46 - 6 
99-0 
55-5 
1-6 
46-2 
96-0 
55-2 
1-9 
46-0 
94-0 
55-0 
2-1 
45-5 
84-5 
54-2 
3-1 
45 - 4 
82-0 
53-6 
4-2 
45-2 
74-0 
53-0 
5-8 
45-0 
65-0 
52-0 
9-6 
44‘9 
59-0 
513 
15-4 
44-8 
53-0 
51-0 
19-4 
44-7 
45-0 
50-6 
267 
44-4 
35-5 
50-3 
36-5 
44-2 
23-5 
50-0 
43-5 
44-0 
16-5 
49-8 
52-0 
43-7 
9-3 
49-7 
56-0 
43-5 
5-5 
49-5 
67-0 
43-0 
2-5 
49-2 
73-0 
42-4 
0 
Energy Curve of visible Prismatic Spectrum. 
Scale reading. 
Intensity. 
Scale reading. 
Intensity. 
56"85 
H 
49-20 
22 
55-90 
5 
48-25 
26 
54-95 
n 
47-30 
32 
54-00 
9 
46-35 
38 
53-05 
10 
45-40 
50 
52-10 
121 
44-45 
64 
51-15 
151 
43 50 
78 
50-20 
18 
42-55 
97 
§ IX. General Remarks on ascertaining the Value of Colour Illumination. 
We may remark that the colour whose illumination we found to be most difficult 
to estimate is green ; as, however, any small difference in the position in the spectrum 
at this part causes but a very small difference in the intensity of the light, the 
measurement can be made with great accuracy. Blue-green is more easily compared. 
We found no difficulty in measuring the red, nor the violet when the brightness is 
fairly powerful. We have already drawn attention to the difficulty of measuring 
near the maximum, and have explained how measurements here can be checked. 
