“Besides learning to see, there is another art to be learned,—­not to see what is not.

“If we read in to-day’s paper that a brilliant comet was seen last night in New York, we are very likely to see it to-night in Boston; for we take every long, fleecy cloud for a splendid comet.

“When the comet of 1680 was expected, a few years ago, to reappear, some young men in Cambridge told Professor Bond that they had seen it; but Professor Bond did not see it.  Continually are amateurs in astronomy sending notes of new discoveries to Bond, or some other astronomers, which are no discoveries at all!

“Astronomers have long supposed the existence of a planet inferior to Mercury; and M. Leverrier has, by mathematical calculation, demonstrated that such a planet exists.  He founded his calculations upon the supposed discovery of M. Lesbarcault, who declares that it crossed the sun’s disc, and that he saw it and made drawings.  The internal evidence, from the man’s account, is that he was an honest enthusiast.  I have no doubt that he followed the path of a solar spot, and as the sun turned on its axis he mistook the motion for that of the dark spot; or perhaps the spot changed and became extinct, and another spot closely resembling it broke out and he was deceived; his wishes all the time being ’father to the thought.’

“The eye is as teachable as the hand.  Every one knows the most prominent constellations,—­the Pleiades, the Great Bear, and Orion.  Many persons can draw the figures made by the most brilliant stars in these constellations, and very many young people look for the ‘lost Pleiad.’  But common observers know these stars only as bright objects; they do not perceive that one star differs from another in glory; much less do they perceive that they shine with differently colored rays.

“Those who know Sirius and Betel do not at once perceive that one shines with a brilliant white light and the other burns with a glowing red, as different in their brilliancy as the precious stones on a lapidary’s table, perhaps for the same reason.  And so there is an endless variety of tints of paler colors.

“We may turn our gaze as we turn a kaleidoscope, and the changes are infinitely more startling, the combinations infinitely more beautiful; no flower garden presents such a variety and such delicacy of shades.

“But beautiful as this variety is, it is difficult to measure it; it has a phantom-like intangibility—­we seem not to be able to bring it under the laws of science.

“We call the stars garnet and sapphire; but these are, at best, vague terms.  Our language has not terms enough to signify the different delicate shades; our factories have not the stuff whose hues might make a chromatic scale for them.

“In this dilemma, we might make a scale of colors from the stars themselves.  We might put at the head of the scale of crimson stars the one known as Hind’s, which is four degrees west of Rigel; we might make a scale of orange stars, beginning with Betel as orange red; then we should have