INTENSITY OE THE CHEMICAL ACTION OF TOTAL DAYLIGHT. 
661 
In order to avoid the necessity of making the foregoing experiments for the calibra- 
tion of every new graduated strip, a series of standard tints * was prepared by reading 
off the points of identical tint on the graduated strip C. The following numbers were 
obtained : — 
Standard tint. 
Mean of ten readings. 
Intensity. 
No. I. . . 
.... 2*56 
II. . . 
. . . 54 
.... 1-90 
III. . . 
... 74 „ 
.... 1-63 
IV. . . 
... 117 „ 
.... 1-14 
Y. . . 
... 132 „ 
.... 1-00 
YI. . . 
... 146 „ 
.... 0-74 
VII. . . 
... 157 
.... 0-54 
VIII. . . 
... 160 
.... 0-50 
IX. . . 
... 164 „ 
.... 0-41 
By means of these standard tints thus calibrated the intensities of any graduated strip 
can be read off. 
III. On the preparation of constant Sensitive Paper in long Strips. 
In the paper already referred tof, it has been shown that sheets of salted paper, each 
having an area of 0‘3 square metre, can be silvered, so that each portion of the sheet, 
after drying, possesses exactly the same degree of sensitiveness. For the purposes of 
the present method the paper has to be used in the form of long thin strips ; and if 
these strips can be silvered in lengths from 1 to 2 metres, and still retain a uniform 
degree of sensitiveness, much labour in cutting up the silvered sheets will be saved. 
That this uniformity can be obtained is seen from the following experiments. 
Salted paper was silvered by laying it, in the form of sheets 2 decims. square, on to 
the surface of a 12 per cent, nitrate-of-silver solution. After lying on the bath for two 
minutes it was hung up to dry. Some of the same salted paper was next cut into long 
strips about 10 to 15 millims. in width, and these were silvered by floating on the silver 
solution contained in a narrow wooden trough 1*5 metre in length ; the strips were 
then hung up to dry. Small pieces were next cut out of both the sheet and strip 
silvered paper, pasted on the back of the ordinary reading strips, and exposed to sun- 
light in two different hand-insolators at the same moment for identical periods of time. 
The tints obtained were read off on a calibrated strip, when it was found that the 
intensities obtained for the tints on the strip and sheet silvered paper were identical, 
as is shown by the following Tables : — 
* Philosophical Transactions, 1865, vol. civ. p. 615, fig. 3. 
f Ibid. 1863, cliii. p. 155. 
