662 
ME. H. E. EOSCOE ON A METHOD OE MEASUEING THE 
Experiment A. 
Paper in 
sheet. 
Paper in 
strip. 
No. 
n. 
Mean 
readi g. 
I. 
I 
No. 
n. 
Mean 
reading. 
I. 
I 
n 
1. 
20 
76 
0-99 
0-049 
1. 
20 
73 
1-03 
0-051 
2. 
15 
117 
0-76 
0-051 
2. 
15 
115 
0-83 
0-055 
3. 
20 
72 
1-04 
0-052 
3. 
20 
56 
1-25 
0-062 
4. 
15 
78 
0-98 
0-065 
4. 
15 
78 
0-98 
0-065 
5. 
10 
79 
0-97 
0-097 
5. 
10 
74 
1-01 
0-101 
6. 
10 
131 
0-66 
0-066 
6. 
10 
115 
0-77 
0-077 
7. 
15 
76 
0-99 
0-066 
7. 
15 
61 
1-20 
0-080 
8. 
10 
114 
0-78 
0-078 
8 . 
10 
113 
0-78 
0-078 
Mean 
0-066 
Mean 
0-071 
Experiment B. 
1. 
10 
128 
0-69 
0-069 
1. 
10 
126 
0-70 
0-070 
2. 
10 
120 
0-75 
0-075 
2. 
10 
122 
0-73 
0-073 
3. 
15 
97 
0-87 
0-058 
3. 
15 
114 
0-78 
0-052 
4. 
5 
153 
0-47 
0-094 
4. 
5 
154 
0-45 
0-090 
5. 
5 
117 
0-76 
0-152 
5. 
5 
131 
0-66 
0-132 
6. 
10 
123 
0-73 
0-073 
6. 
10 
125 
0-71 
0-071 
7. 
5 
140 
0-60 
0-120 
7. 
5 
139 
0-61 
0-122 
8. 
5 
135 
0-63 
0-126 
8. 
5 
140 
0-60 
0-120 
9. 
5 
141 
0-59 
0-118 
9. 
5 
142 
0-58 
0-116 
Mean 
0-098 
Mean 
0-094 
The mean intensity obtained by insolation of paper in sheet from the two experi- 
ments is therefore ° ^ Q - Q98 — 0082 ; that obtained by the insolation of paper cut 
into strips and silvered is ° Q94 = 0-082. Hence we may conclude that the 
method of silvering the paper in strips can be relied upon. 
IV. Determination of the Times of Exposure of the constant Sensitive Paper in 
the Insolator. 
The time during which each one of the disks of sensitive paper is exposed to the 
total daylight depends upon the length which elapses between the contact of the elastic 
arm (E, fig. 1) with the two consecutive platinum pins on the wheel D. A certain 
time, how’ever, elapses after the passage of the current before the escapement-wheel 
(F, fig. 2) on the insolator is brought into motion and the paper thus moved. It 
therefore becomes necessary to ascertain the times of exposure for each particular inso- 
lator, by observing the moment at which the paper is released, and noting the space of 
time which elapses until the paper disk disappears. The estimation of these intervals, 
some of them of only short duration, was made with a chronograph kindly lent by 
Mr. J. B. Dancer, by which intervals of time could be accurately measured to within 
