INTENSITY OF THE CHEMICAL ACTION OF TOTAL DAYLIGHT. 
665 
Time. 
Coefficient for 
glass shade. 
Deviation 
from mean. 
h m 
11 0 A.M. 
1-857 
-0-080 
2 0 p.m. 
2-000 
+ 0-063 
2 30 „ 
1-950 
+ 0-013 
3 0 „ 
1-902 
-0-035 
3 30 „ 
1-718 
-0-219 
4 0 „ 
1-939 
+ 0-002 
4 30 „ 
2-189 
+ 0-252 
5 0 „ 
j 
1-941 
+ 0-004 
| 
Mean 
1-937 
0-083 
VI. Comparison of Curves of Daily Chemical Intensity obtained (1) with the Hand - 
insolator and (2) with the Self-recording Instrument. 
During the months of May, June, and July 1873 simultaneous hourly determinations 
of the chemical intensity of total daylight were made in Victoria Park, Manchester, 
with the hand-insolator and the self-recording arrangement described above on twelve 
separate days, whils't on ten other days the intensity was ascertained by the automatic 
apparatus alone. Of these I deem it unnecessary to give the details of more than six 
full days’ observations with both instruments for the purpose of showing that the che- 
mical intensities, as measured by the two methods, closely agree, and that therefore 
the self-recording instrument gives reliable and accurate results. 
The daily observations selected for this purpose were made on May 17th and 19th, 
June 9th, 17th, and 18th, and on July 1st. The following Tables and accompanying 
curves (fig. 4, Plate L.) show the close correspondence of both sets of observations. 
The Curves marked in thicker lines give the results of r the hand-insolator measurements, 
those in thinner lines the results of the measurements recorded by clockwork. 
The integrals of total chemical intensity* for six of the days on which simultaneous 
observations were made with the two instruments agree as closely as can be expected 
from the nature of the case. 
Daily Integrals of Chemical Intensity determined 
(1) By clock instrument. (2) By hand instrument. 
May 17th . 82-8 81-6 
„ 19th 49-5 ....... 47-2 
June 9th 87-1 96-7 
„ 17th 51-0 52-2 
„ 18th 52-2 47-4 
July 1st 111-2 117-3 
I have to thank Mr. Thomas Carnelley, B.Sc., for the able assistance which he has 
given me in carrying out the above determinations. 
* Philosophical Transactions, “ Bakerian Lecture,” 1865, vol. civ. p. 621. 
4 u 2 
