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758 chapters on the lunar motions in his 'Outlines of Astronomy.' I was thus able to correct any errors in my own work, while in turn I detected a few (mentioned in the notes) in the works referred to. I have adopted a much more complete and exact system of illustration in dealing with the moon's motions than either of my predecessors in the explanation of this subject. I attach great importance to this feature of my explanation, experience having satisfied me not only that such matters should be very freely illustrated, but that the illustrations should aim at correctness of detail, and (wherever practicable) of scale also. Some features, as the advance of the perigee and the retreat of the nodes, have, I believe, never before been illustrated at all."

In Chapter III. Mr. Proctor gives, among other matters, a full explanation of the effects due to the strange balancing motion called the lunar librations. He says: "I have been surprised to find how imperfectly this interesting and important subject has been dealt with hitherto. In fact, I have sought in vain for any discussion of the subject with which to compare my own results. I have, however, in various ways sufficiently tested these results."

But probably, to the greater number of readers, the main interest of the book will be found in the chapters relating to the condition of the moon's surface—the mountains, craters, hills, valleys, which diversify its strange varieties of brightness, color, and tone, and the changes of appearance which are noted as the illumination varies, and as the lunar librations change the position of different regions. It is, by-the-way,to be noted that the moon, which we regard as of silvery whiteness, is in reality more nearly black than white, a fact which will recall to many of our readers a remark of Prof. Tyndall's in the first lecture of the course recently delivered here.

"The moon appears to us," he said, "as if

but, were she covered with the blackest velvet, she would still hang in the heavens as a white orb, shining upon the world substantially as she does now."

Mr. Proctor discusses also the phenomena presented to lunarians, if such there be. The extreme rarity of the lunar atmosphere renders the idea of existence on the moon rather strange to our conceptions, but, as Sir J. Herschel has said in a similar case, "we should do wrong to judge of the fitness or unfitness of" the condition of lunarians "from what we see around us, when perhaps the very combinations which convey to our minds only images of horror may be, in reality, theatres of the most striking and glorious displays of beneficent contrivance." Speaking of the appearances presented by lunar landscapes, two of which we borrow from his work, Mr. Proctor remarks