382 JOURNAL OF THE PLYMOUTH INSTITUTION. 
which induce astronomers to believe that the planets around them 
are inhabited, as they show the lines common to those substances 
that have to do with animal existence on our own world. The gas 
streams of the sun, which are projected to vast heights from the 
surface, are of hydrogen. Their rate of progress and decrescence is 
plainly and easily calculated by means of the spectroscope. The 
rate of motion of stars, as regards our earth, can be found out in 
the same way. Solutions of substances in glass cells interposed 
in the spectroscope are found to affect the lines much. The 
purity of many substances can be tested by the way in which 
the solution affects the spectrum. 
Part II. 
(Read March 11, 1875.) 
Besipes the division into colours, the spectrum was shown to be 
divided into heat rays, chemical rays, and light rays. The heat 
rays were situate at the red end, and outside the light rays the 
intensity was at its greatest. The rays behaved as the light rays 
in their reflection and refraction. A cell of iodine dissolved in 
bisulphide of carbon sifted out all the light, but allowed all the 
heat to pass, and substances were raised to a white heat at the dark 
focus. Chemical rays were situate at the violet end and beyond it. 
They were the rays of the photographer. They also were active in 
the production of colour in plants in the spring, when they are most 
energetic. The general rules of photography were explained, the 
camera, focussing, collodion, bath, developer, and fixing solution. 
A photograph was taken by the aid of the lime light, the various 
parts of the process being explained. Printing was explained, and 
also the Johnson autotype and the heliotype process. Various 
instances of phosphorescence and fluoreescence were shown and 
explained. The laws of diffraction, interference of light were 
touched upon, and the phenomena produced shown and explained. 
The fringes of monodramatit and compound light, Grimaldi’s lines 
and Fresnel’s experiments, the action of gratings, small apertures, 
and crossed fine lines were explained ; also the colours of thin 
plates. The next subject was polarization of light. This was 
shown by means of the tourmaline plates, the Nicol prisms, and the 
bundles of plates of glass. Many pictures of selenite were shown, 
descriptive of the alteration of colour on turning the analyser, 
