32 . REPORT—1846. 
effected by. the increased or diminished intensity of the luminous and calo- 
rific rays, and consequently that even the actinism residing in the extreme 
violet ray is relatively as much influenced by an increase of luminous power 
as that which is detected in the yellow ray itself, we may by the use of the 
paper prepared with the ammonio-nitrate of silver arrive at a very close ap- 
proximation to the true result. 
Although I have not been enabled to realize the hope I held forth last year 
of presenting at this meeting a register of actinic influences for the year,(which _ 
I have been prevented from doing by circumstances which I shall presently 
explain, ) yet I have determined, most satisfactorily te my own mind, the prac- 
ticability of procuring, in favourable positions, such a registration as shall 
afford much valuable information. 
The circumstances to which I allude as those which have prevented my 
procuring any series of registers, are the impossibility of securing in London 
any position free from the constant interferences of smoke and fog, and the 
difficulty of placing the instrument so as to be free from the reflected radia- 
tions of adjoining buildings. The first alone is a fatal objection ; for instead 
of securing, what is desired, a registration of the relative amount of chemical 
influence as compared with the quantity of light, heat, and the natural at- 
mospheric conditions, we only get a register of the influence of smoke in 
absorbing the actinic rays. 1 therefore propose to hand over the instrument 
to the Association, requesting that it may be placed in a favourable position 
at Kew, under the attention of the excellent observer there, when I do not 
doubt some curious and instructive results may be obtained. 
It is necessary however to state that my experience has pointed out some 
objections to this mode of registration, which indeed militates against the 
use of the actinograph as a philosophical instrument. 
It is a curious fact that upon almost all kinds of photographic paper the 
colour produced by the solar rays at different periods of the day varies 
considerably. It is not a mere difference of tint, but an actual change in the 
colour; thus frequently the light of both morning and evening will give to 
chloride of silver a rose hue, whilst that of noon will change it to a bluish 
variety of brown. ‘There is consequently much difficulty in deciding which 
is the strongest impression. Thus also the rays upon two days, when the sun 
appears equally bright, will in one case produce a red brown, and in the other 
a blue brown. It is left to the eye to decide upon the intensity of the effect 
produced, and with the utmost care it is frequently impossible to say whether 
the actinic influence is greatest on the red brown lines, or those which are 
blue brown. 
The importance of the inquiry has been peculiarly evident during this 
summer; many peculiarities have been observed in the growth of plants, in- 
fluenced no doubt by the solar radiations. Many of our garden flowers, 
particularly roses, have exhibited an abnormal condition, leaf-buds being 
developed in the centre of the flower, arising from the vegetative functions 
of the plant overpowering its reproductive functions. Again, during the 
intense sunshine and the prevalence of the unclouded skies of the hot wea- 
ther of June and July, practical photographists found the greatest difficulty — 
in obtaining portraits by the Daguerreotype process. At this time, although 
the intensity of effect produced on paper in the actinograph under the usual 
circumstances of summer sunlight should have been at a maximum, it was 
found that it was far below this point, the maximum point being repre- 
sented by 120. During several experiments made at the time mentioned, the 
greatest effect indicated was 100; whilst the sky still being unclouded and — 
the sun shining brightly, it often fell to 90, and sometimes indeed to 80. 
eh are 
