Physics and Chemistry. 403 
chromosphere, when cool enough to absorb, is still of a relatively 
high temperature. 
If. Under certain conditions of temperature and pressure, the 
very complicated spectrum of hydrogen is reduced in our instru- 
ment to one line in the green corresponding to F in the solar 
spectrum. 
{IL The equally complicated spectrum of nitrogen is similarly 
reducible to one bright line in the green, with traces of other more 
refrangible faint lines, 
rom a mixture of the two gases we have obtained a com- 
bination of the spectra in question, the relative brilliancy of the 
two bright green lines varying with the amount of each gas pres- 
ent in the mixture. 
. By removing the experimental tube a little farther away 
from the slit of the spectroscope, the combined spectra referred to 
in If and ILI were reduced to the two bright lines. 
VI. By reducing the temperature all spectroscopic evidence of 
the nitrogen vanished; and b increasing it, many new nitrogen 
= ee their appearance, the hydrogen line always remaining 
visible, 
se spectrum 
hot extend from pole to pole, but is only visible fora small distance 
Indicated by an atmosphere of magnesium around each boc. the 
sun. e most 
¢ authors consider this experiment as fully justifying their as- 
sumption that the mass of the absorption takes place in the photo- 
sphere and that this and the erg it constitute the true at- 
mosphere of the sun—Proc. of the Royal Society, vol. xvii, 288, 
453. Comptes Rendus, xix, 264. : Os 
4. On the physical constitution of the Sun.—In a letter ad- 
dressed to M. Dumas and by him communicated to the Academy 
t Science ; iven a summary of his observa- 
ry. 
sr La adng i tee alae Seto: Oct. 20, 1868. 
lier eee. (if eames Dee. 20, ; 
Meets : : 
March 14, 1869. 
