its power; and to cooling, the possibility of its expression.
For the steps in the chemical process from Sun to habitable Earth we must look to the spectroscope; not in its older field, the blue end of the spectrum, but in that which is unfolding to our view in Dr. Slipher's ingenious hands, the extension of the observable part of it into the red. For at that end lie the bands due to planetary absorption. Here we have already secured surprising results as to the atmospheres of the various planets. We have not only found positive evidence of water-vapor in the atmosphere of Mars, but we have detected strange envelopes in the major planets which show a constitution different from that of the Sun on the one hand, and of the Earth on the other. That size and position are for much in these peculiarities, I have already shown you; but something, too, is to be laid at the door of age. The major planets are not so advanced in their planetary history as is our Earth; and Dr. Slipher's spectrograms of them disclose what is now going on in that prefatory, childish stage.
These spectrograms are full of possibilities, and it is not too much to say that chemistry may yet be greatly indebted to the stars. Compounds, the strange unknown substances there revealed by their spectral lines, may be cryptic as yet to us. Some of the elements missing in Mendeléeffs table may be there, too. Helium
