758 THE POPULAR SCIENCE MONTHLY. 



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 de- 

 tected 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 feat- 

 ure of my explanation, experience having satisfied me not only that 

 such matters should be very freely illustrated, but that the illustra- 

 tions 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 diver- 

 sify 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 



' Clothed in white samite, mystic, beautiful,' 1 



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 ren- 

 ders the idea of existence on the moon rather strange to our concep- 

 tions, 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 luna- 

 rians " from what we see around us, when perhaps the very combina- 

 tions which convey to our minds only images of horror may be, in 

 reality, theatres of the most striking and glorious displays of benefi- 

 cent contrivance." Speaking of the appearances presented by lunar 

 landscapes, two of which we borrow from his work, Mr. Proctor remarks 



1 "We quote Tyndall. Tennyson wrote : 



" Clothed in white samite, mystic, wonderful." 



