REGISTRATION OE THE CHEMICAL ACTION OF TOTAL DAYLIGHT. 
609 
time determined. It appears, from a large number of such comparisons, a few of which 
only are given below, that in almost all cases an irregular, and in some instances a rapid 
fading takes place immediately after the strips have been prepared, and that this fading 
continues for about six to eight weeks from the date of the preparation. It is, however, 
seen that, after this length of time has elapsed, neither exposure to sunlight nor preser- 
vation in the dark produces the slightest change of tint, and that, for many months 
from this time forward, the tint of the strips may be considered as perfectly unalterable. 
(1) Experiments showing the alteration of tint ensuing immediately after preparation. 
Each number given below represents the intensity (see Table II., p. 159 of the last 
memoir) corresponding to the mean of ten independent readings on each strip upon the 
under-mentioned days. 
Sheet No. 1, prepared December 9, 1863, 
Intensity. 
1st Reading, 
Dec. 16, 1863. 
Intensity. 
2nd Reading, 
Jan. 7, 1864. 
Diminution in 
three weeks. 
Strip A, exposed to sunlight... 
2*49 
2-05 
0*44 
Strip B, preserved in the dark 
2-49 
2*01 
0-48 
Sheet No. 2, prepared December 9, 1863. 
Strip A, exposed to sunlight... 
2-21 
1-86 
0-35 
Strip B, kept in the dark 
2-21 
2-03 
0-18 
From these numbers it is seen that the fading which occurs immediately after pre- 
paration is not dependent upon exposure, a change of the same kind being observed in 
those strips which were protected from the action of light. 
(2) Experiments showing the permanency of tint after lapse of some time from date of 
preparation. 
Sheet No. 
3, prepared September 21, 1863. 
Intensity. 
Intensity. 
Intensity. 
Intensity. 
1st Reading, 
2nd Reading, 
3rd Reading, 
4th Reading, 
Dec. 10, 1863. 
Dec. 18, 1863. 
Jan. 11, 1864. 
Feb. 4, 1864. 
Strip A, exposed to sunlight... 
1*40 
1-40 
1-38 
1-36 
Strip B, kept in the dark 
1-38 
1-37 
1*39 
1-35 
Sheet No. 4, prepared September 21, 1863. 
Strip A, exposed to sunlight... 
1*45 
D39 
1-39 
1-38 
Strip B, kept in the dark 
1-43 
1-43 | 
1-45 
1-46 
