02 



KNOWLEDGE 



[Makch 1,1901. 



length, iiorlh and soutb, is but 280. It is thus elliptical 

 ill reality, as it is also in appearance, but its major axis, 

 thi'ough the effect of foreshortening, shows as if it were 

 the minor. 



The Mare Crisium was the subject of the Plate in 

 Knowledge for March, 1899, two years ago ; but it was 

 then shown under sunset illumination, whilst in tlie 

 present Plate, the morning light is full upon it. The 

 western border, therefore, was entirely lost in night in 

 the former rejaresontation, and the eastern highlands 

 were too strongly illuminated for their intricacies to be 

 followed as clearly as they can be now. The magnificent 

 rnountain group which forms the southern boundary of 

 tlie Mare, can also be examined better under the present 

 lighting; its broad deep bays and winding valleys being 

 seen under the most favourable conditions. 



The western frontier is cjuite of a different character 

 from the others, being a broad, gently sloping plateau; 

 and the extension on the west of the Mare which begins 

 under the shelter of the great southern promontory. 

 Cape Agarum, and which appears on the photograph 

 to be marked olf from the mam body of the Mare by a 

 very distinct ridge, would seem probably to be a later 

 development, an annexation after it had attained its 

 original form of a nearly perfect hexagon. 



The centre of the Plate is occupied by the Sea of 

 Plenty, which however is not shown here quite in its 

 entirety. It covers an area of 160 thousand square miles, 

 stretching some 640 miles front north to south, 410 from 

 east to west. It narrows, however, greatly towards the 

 south, being onl}' 130 miles wide where Yendelinus 

 borders it, so that its shape as a whole is that of a pear. 

 The photograph brings out in strong relief the successive 

 ridges by which the plain rises from its lowest depth, — 



Ansganus 

 U PeyrobS) 



Magethaens 



Maclaunn h/) 



Coiidorcel 

 Hansen^ 

 AlhazenV) yV^'^wn 



Sketch Mup. 



situated almost precisely at the centre of the Plate, — up 

 to its western border, and which mark the stages of the 

 subsidence of the crust. 



Immediately to the west of the Mare, is the beautiful 

 walled plain of Langrenus, which in the completeness of 

 the example which it offers of eruptive action may 

 be considered the Copernicus of this region of the moon, 

 and indeed it is not much inferior to the latter in perfect- 

 ness of outline, whilst it considerably exceeds it in 

 dimensions. The walls of Langrenus, however, do' not 

 rival those of Copernicus in height, and its system of 

 light streaks falls far short of that which crowns the 

 beauty of the monarch of the Carpathians. The great 

 walled plain at the top of the photograph is Petavius, 

 nearly 80 miles in cliametci", surrounded by a lofty 

 mountain wall, double on nearly every side but the north, 

 where it is lower and broader. T^vo of the leading 

 features of the formation come out on the photograph 

 with especial distinctness; one the central peak, and the 

 other the rill that leads from it in a south-easterly 

 direction, right up to the wall of the plain. 



Between Petavius and Langrenus lies Yendelinus, a 

 walled plain as extensive as its tw'o neighbours, but 

 destitute of their sjinmctry and completeness, but for 

 that very reason a more interesting region to study. 

 Midway between Petavius and Veudelinus, but iurther 

 from the limb, is Petavius B, a deep ring plain, standing 

 in a bright elevated region. The brightness of this 

 region renders it one of the most conspicuous markings 

 in the Plate, and is an evidence of its relative newness. 



A very cursory glance at the limb of the Moon is 

 sufficient to show that it is far from being a true curve, 

 a very distinct flattening being very perceptible about 

 the centre. This is of especial interest, inasmuch as it 

 gives some suggestion of an answer to the question we 

 so vainly ask, " What does the other side of the moon 

 look like V It would seem that we have here another 

 of the great grey plains which on the visible disk we call 

 iiiaria. It is the Mare Smythii, and its presence justifies 

 us in inferring that the unseen three-sevenths of the 

 moon's spherical surface does not materially differ in 

 general character from the four-sevenths we know. Like 

 it, it would present, could we examine it, bright broken 

 highlands and broad sombre plains, and every variety 

 of lunar structure from the great walled i^lain to the 

 smallest craterlet. - . - 



Hftttrs. 



[The Editors do not hold themselves responsible for the opinions 

 or statements of correspondents.] 



THE PATH OF THE SUN. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — In the notice of my work under the above title 

 ill your January issue, an adverse opinion is expressed, 

 and with your permission I desire to suggest a refei'euee 

 to facts of such a character that they will either effectually 

 destroy my theory of the Sun's course or establish its truth. 



Just as it is essential for the truth of precession that 

 the south pole of the heavens should descril)e a similar 

 circle to that of the north jiole, so is it requisite for the 

 establishmeut of my case that the south ])ole should not 

 move in a circle but remain in one spot ; and if proof of 

 its motion can be furnished, I will admit tbe fallacy of my 

 arguments. 



If, on the contrary, observations show that the south 

 pole is a fixture, no other theory but mine can account for 

 such a phenomenon ; nor can the doctrine of precession be 

 maintained in face of a fact so coutradictory. 



I will only add that while abundance of evidence exists 

 a.s to the present position ani revolution of the uorth 



