The spectrograms in question were made possible by his production of a new kind of plate. His object was to obtain one which should combine sufficient speed with great photographic extension of the spectrum into the red. For it is in the red end that the absorption lines due to the planets’ atmospheres chiefly lie. With the plates heretofore used it was impossible to go much beyond the yellow, the C line marking the _Ultima Thule_ of attent. Not only was it advisable to get more particularity in the parts previously explored, but it was imperative to go beyond into parts as yet unknown. After several attempts he succeeded, the plates when exposed showing the spectra beyond even the A band. Of their wealth of depiction it is only necessary to say that in the spectrum of Neptune 130 lines and bands can easily be counted between the wave-lengths 4600 µµ, 7600 µµ. Of these, 31 belong to the planet, which compares with 6 found by Huggins, 10 by Vogel, and 9 by Keeler in the part of its spectrum they were able to obtain. [Illustration: THE SPECTRA OF THE MAJOR PLANETS. _Photographed, in 1907, by V. M. Slipher, at THE LOWELL OBSERVATORY Flagstaff, Arizona._] The result was a revelation. The plates exposed a host of lines never previously seen; lines that do not appear in the spectrum of the Sun, nor yet in the added spectrum of the atmosphere of the Earth, but are due to the planets’ own envelopes. But this was only the starting-point of their disclosures. When in this manner he had taken the color signatures of Jupiter, Saturn, Uranus, and Neptune, an orderly sequence in their respective absorption bands stood strikingly confessed. In other words, their atmospheres proved not only peculiar to themselves and unlike what we have on Earth, but progressively so according to a definite law. That law was distance from the Sun. When the spectra were arranged vertically in ordered orbital relation outward from the Sun, with that of the lunar for comparison on top, a surprising progression showed down the column in the strange bands, an increase in number and a progressive deepening in tint. The lunar, of course, gives us the Sun and our own air. All else must therefore be of the individual planet’s own. Beginning, then, with Jupiter, we note, besides the reënforcement of what we know to be the great water-vapor bands ‘_a_,’ several new ones, which show still darker in the spectrum of Saturn. The strongest of these is apparently not identifiable with a band in the spectra of Mira Ceti in spite of falling near it. Passing on to Uranus, we perceive these bands still more accentuated, and with them others, some strangers, some solar lines enhanced. Thus the hydrogen lines stand out as in the Sirian stars. All deepen in Neptune, while further newcomers appear.