760 REPORT— 1890. 
second or back screen is then placed at the mouth of these cones, over which it fits 
and effectively cuts off one light from the other, so that on one side, say, is the 
electric light, on the other is the standard candle. The light from both passes 
through the axis of their respective cones, through the discs and on to the screen, 
upon which the shadow-image is cast. 
9. On a Radiometric Record of Sun-heat from different parts of the 
Solar Disc. By W. EB. Witson. Communicated by Professor G. F. 
FirzGurawp, F.R.S. 
The author had represented, by means of a photograph curve, the variation of 
the effect on a radio-micrometer, 2mm. in diameter, as the image of the sun, 80 
cm. in diameter, passed over the instrument. The curve is not a smooth one, and 
in the opinion of the author the cause of the unevenness lies in the uneven 
amount of radiation from the different parts of the sun’s disc. 
10. Recent Photographs of the less refrangible portions of Solar Spectrum 
under different Atmospheric Conditions. By Grorce Hices. 
During the last few months the author has endeavoured to photograph under 
ag many conditions as possible the atmospheric absorption regions of the solar 
spectrum. A number of results have been obtained within a few minutes after 
sunrise, some of which include the great A line at the extreme end of the visible 
red, and, judging from eye observations, it is supposed that this group is almost 
constant in intensity. 
The photographs show, however, that it is quite as variable asthe Bline. The 
paper prints represent the head and portion of fluting, a few of the fainter lines 
are lost through under-development, but what may be photographed with a hich 
sun, using the second order spectrum, is fairly represented. 
Original negatives of a very low sun show the head as one broad line, whereas 
between forty and fifty may be counted with midday sun; a corresponding nebulo- 
sity broadens the lines composing the tail, which becomes irresolvable. 
In about an hour after sunrise the thick band begins to break up in the region 
of the edge; the general nebulosity decreases but never disappears entirely, even 
with 12 o'clock sun. 
The B group photographed under similar circumstances might easily be mis- 
taken for that of A with a high sun, but the relative variability of the two lines is 
apparently the same, and has doubtless the same common origin. 
I believe that Professor Liveing has shown both to be due to oxygen. 
A sufficient number of photographs of these portions, together with those em- 
bracing little a, C, a, the so-called rain bands and atmospheric zones, w. 1. 5,700, 
have been taken to show the existence of other sets of lines whose variation in 
intensity is still greater than that of A and B. 
To complete the work in the regions referred to, other photographs are still 
required, and provision has been made to enable photographs to be taken during dry 
and frosty weather, to facilitate comparison by inspection with those already taken, 
where the quantity of aqueous vapour was considerable. 
Some photographs of the invisible red, w. 1. 8,350, will also show those lines 
which have a tellurie origin. 
itd a 
