Note 24 — THE SUN—WHAT WE LEARN FROM IT.—Richard A. Proctor
Reading edition
To these may be added the following law:
4. Light reflected from any opaque body gives the same spectrum as it would have given before reflection.
5. But if the opaque body be surrounded by vapors, the dark lines corresponding to these vapors make their appearance in the spectrum with a distinctness proportioned to the extent to which the light has penetrated those vapors before being reflected to us.
6. If the reflecting body be itself luminous, the spectrum belonging to it is superadded to the spectrum belonging to the reflected light.
7. Glowing vapors surrounding an incandescent source of light may cause bright lines or dark lines to appear in the spectrum, according as they are more or less heated; or, they may emit just so much light as to make up for what they absorb, in which case there will remain no trace of their presence.
8. The electric spark presents a bright-line spectrum, compounded of the spectra belonging to the vapors of those substances between which, and of those through which, the discharge takes place. According to the nature of these vapors and of the discharge itself, the relative intensity of the component parts of the spectrum will be variable.
Lastly, the appearance of the spectrum belonging to any element will vary according to the circumstances of pressure and temperature under which the element may emit light.