90 
POPULAB SCIENCE BE VIEW. 
“ presence in the spectra of these planets of lines and hands of absorption, 
identical with those produced in our atmosphere, seems,” he says, “ to prove 
the existence of aqueous vapours in the gaseous envelopes of these planets, 
so that it seems difficult to suppose the temperature of their surface high 
enough to cause an emission of light.” The argument is weak, however. 
We know that in the higher regions of our air there are often, if not gene- 
rally, minute crystals of ice, forming light cirrus clouds. If an inhabitant 
of Venus or Mercury could become cognizant of the existence of these ice- 
crystals, he might infer, from M. Vogel’s method of reasoning, that the 
temperature of the earth’s surface could not he higher than the freezing 
point of water. He would be mistaken ; and quite probably M. Vogel is 
mistaken, on this particular point. “ The solar and the planetary spectra 
differ,” he says, “ in that the latter have absorption bands, more or less 
intense, in the less refrangible parts ; and these may be attributed to the 
atmospheres of the planets. The further a planet is from the sun, the more 
preponderating is the influence of its atmosphere. The interior planets, 
Mercury and Venus, have only very weak absorption bands in the red and 
yellow, which are coincident with lines produced by the passage of light 
through our atmosphere. Mars presents the same bands, but more marked. 
In the spectra of Jupiter and Saturn, there is, besides these bands, a very 
intense band in the red ; and all the more refrangible part (violet and blue) 
is greatly weakened, without bands being distinguishable. Lastly, the 
spectra of Uranus and Neptune are crossed everywhere with broad and 
intense absorption bands.” These results agree in the main with those 
already obtained by Mr. Huggins. (See also an article by Mr. It. A. 
Proctor, “On the Condition of the Larger Planets,” at p. 38 of the present 
number.) 
Effect of Sunspots on Terrestrial Climates . — Professor S. P. Langley has 
endeavoured to ascertain by how many points of a degree Centigrade the 
earth’s mean annual temperature necessarily varies between a year of 
maximum and a year of minimum spot areas, so far as the immediate effect 
of these on the solar thermal radiations is concerned. To do .this, it is 
necessary, he says, “ First to procure from experiment, trustworthy 
measurements of the relative amounts of photospheric, penumbral, and 
nmbral radiation secondly, to determine the relative photospheric, pe- 
numbral, and umbral surfaces, in a maximum and minimum year, and 
(having suitably combined these data) to show, thirdly, within what spe- 
cific limits we can assert that the terrestrial temperature will necessarily be 
changed.” One rather important point may be added as absolutely essen- 
tial to the formation of an opinion from direct observation, viz., we must 
determine whether the radiation from the photosphere remains unchanged, 
or if not, how it varies, with the changing condition of the sun as regards 
the spots. It may be that the increased activity certainly prevailing when 
spots are numerous increases the general radiation from the photosphere, 
and that, too, in a much greater degree than the sunspot area reduces the 
extent of photospheric surface. Having unfortunately omitted to make any 
observations bearing on this point, probably the most important in the whole 
inquiry, Professor Langley’s results are pro tanto reduced in value. They 
are these, — that (neglecting the point just mentioned) the least change in 
