1864. | Physics. 695 
certain standard. Dr. Woods* now suggests a plan which he adopted 
in 1854+ to show the identity of the sun’s action on a photographic 
surface with that of flame, the centre rays of the latter being also more 
intense in chemical action than those at the circumference. ‘his 
method consists in exposing the prepared paper to the sun’s picture in 
the camera for a period so short that the centre or most active rays 
only have time to act upon it; then, for the next impression, to leave 
the paper exposed for a somewhat longer time, so that a somewhat 
larger picture is obtained ; and so on until the entire picture is given. 
The size of the impression produced would be in proportion to the 
time of exposure, and it would appear that the intensity of the chemical 
rays from any part of the dise would be more accurately fixed by get- 
ting the time required for their action than by the use of standard 
tints. 
An important contribution to our knowledge of the light from 
certain of the fixed stars has been presented to the Royal Society by 
Mr. Huggins and Dr. Miller. These gentlemen use in their spectro- 
scope two dense flint-glass prisms, and the spectrum is viewed through 
a small achromatic telescope, with a magnifying power of between five 
and six diameters. A plano-cylindrical lens of 14-inches focus is 
employed to convert the image of the star into a narrow line of light, 
which is made to fall upon a very fine slit, behind which is placed an 
achromatic collimating lens. The spectroscope so constructed is 
attached to the eye-end of a refracting telescope of 10-feet focal length 
with an 8-inch achromatic object-glass, and the whole is mounted 
equatorially and carried by a clock-movement. By this instrument 
between forty and fifty of the fixed stars have been more or less com- 
pletely examined, and tables of the measures of about 90 lines in 
Aldebaran, nearly 80 in a Orionis, and 15 in 6 Pegasi are given. In 
the spectrum of Aldebaran, coincidence with nine of the elementary 
bodies has been observed, viz. sodium, magnesium, hydrogen, calcium, 
iron, bismuth, tellurium, antimony, and mercury. In the spectrum of 
« Orionis, five cases of coincidence were found, viz. sodium, magnesium, 
calcium, iron, and bismuth. £$ Pegasi furnished a spectrum closely 
resembling that of a Orionis in appearance, but much weaker. It was 
particularly noticed that the lines C and F, corresponding to hydrogen, 
which are present in nearly all the stars, are wanting in these two 
stars. In the concluding portion of their paper, the authors apply the 
facts observed to an explanation of the colours of the stars. They 
consider that the difference of colour is to be sought in the difference 
of the constitution of the investing stellar atmospheres, which act by: 
absorbing particular portions of the light emitted by the incandescent 
solid or liquid photosphere, the light of which in each case they sup- 
pose to be of the same quality originally, as it seems to be independent 
of the chemical nature of its constituents. 
The subject of stellar and planetary spectra has been likewise 
continued by Father Secchi. Taking advantage of the moon being in 
the neighbourhood of Jupiter and Saturn, he has compared the spectra 
of the three, and has satisfactorily made out*the presence of atmo- 
* «Phil. Mag.’ August, 1864. 7 ‘Phil. Mag’ July, 1854. 
