June 1, 1892.] 



KNOWLEDGE 



115 



50 miles in diameter, were in some way blown out explo- 

 sively. 



What 1 desire to point out is tlie improbability — not 

 to say the impossibility — of this being done by volcanic 

 action, as we understand it nowadays, and at a time when 

 the lunar crust, to the very surface, must have been far 

 above the boiling point of water. " Without water there 

 can be no volcano," and hence, with such a high tem- 

 perature, there being no irater, there could have been no 

 volcano. There is no escape from this syllogism. 



But another weighty argument against the lunar 

 craters being due to volcanic action is their vast size. 

 This is usually accounted for by the fact that lunar gravi- 

 tation is but one-sixth of ours, thereby enabling an " explo- 

 sion" to eject matter to six times the distance. When we 

 look into the case, however, we notice that these lunar 

 " safety valves" are only loaded with one-sixth the terrestrial 

 weights. The explosive force, or accumulated ejecting 

 power (due to steam held under superincumbent pressure), 

 is thus reduced in the same ratio, and the power of ejecting 

 matter on the earth and moon is the same. The power not 

 being derived from any explosive material, such as 

 dynamite, but being controlled by gravitation, the fallacy 

 of the old reasoning is obvious. 



Again, by all accounts our moon at one time rotated on 

 its axis more rapidly, and has been slowed down by vast 

 tides. 



If these were of unter, it is clear that the globe had 

 (then) cooled down so far as to be practically rigid, and 

 the tidal deformation (as in our case) was confined to the 

 tiuid envelope, which thus needs must have scoured off all 

 the " cinder rings," and completely filled in the craters 

 and sunk plains, large and small, the ellipsoidal figure 

 of the globe, so strongly insisted on by Proctor (as a true 

 cause for Ubration), arising subsequently. 



If, however, the era of tidal retardation occurred while 

 the globe was in the semi-molten and plastic condition, as 

 Sir E. S.Bali suggests, then the formation of the walled 

 plains (lava lakes) and volcanic craters must have taken 

 place later on, yet still in the absence of water, inas- 

 much as there is no e%ideuce of its presence then nor yet 

 afterwards, when, if anything, it- should have been still 

 more obvious : when one would very naturally expect the 

 enormous atmosphere of vapours to fall by condensation 

 and scour the surface persistently for long ages durinfi the 

 sloir diclini' i)i tewiieratiiir, at last, perhaps, leading to a 

 development of polar caps and general glaciation. 



There is abundant and beautiful evidence in the sur- 

 facing of the absence of water, during its formation, and 

 this very evidence, 1 hold, is fatal to any theory of volcanic 

 surfacing, for which water is an essential element. Even 

 the poles are covered by vast lava lakes, " cinder rings," and 

 so-called volcanoes. 



This singular absence of all traces of water, all sculpturing 

 by rivers, and of drainage phenomena in the limar sur- 

 facing, is the great problem which needs solution : whether 

 an era of erosion with deposition of stratified rocks and 

 formation of river valleys is, or is not, logically a necessary 

 se(jiiL'l to a semi-molten stage in planetary evolution ; 

 whether a planet could pass from the molten to the airless 

 and waterless stage, and yet retain all through the later 

 stages the surfacing due to a primeval igneous era. 



To me it seems easiest to assume that the moon has 

 long ago passed through our terrestrial erosive stage, and 

 now, in its airless and waterless condition, is swathed from 

 pole to pole in snow and ice formations. 



Sibsagar, Assam, 15th March, 1892. S. E. Peal. 

 [While agreeing with Mr. Peal that the traces of water 



action upon the moon are not conspicuous, I do not feel 

 sure that there is no evidence of sculpturing by rivers or 

 drainage phenomena. Mr. Xeison, in his book on " The 

 Moon," p. 73, is inclined to think that in many points the 

 rills or clefts " bear some resemblance to the dried beds of 

 lunar watercourses or rivers. Thus many of these riUs 

 commence at the end of a system of branched valleys 

 leading from a highland, whilst others can be detected 

 winding along the bottom of extensive valle}* regions." It 

 seems to me also that many of the dark delta-shaped 

 patches, which are frequently found in the planes round 

 lunar momitains, afford evidence of drainage phenomena. 

 There are two such patches on either side of the lunar 

 Appeunines, which are well shown on photogi'aph No. 1, 

 published with the number of Knowledge for December, 

 1890, and three such dark patches to the west of Copernicus 

 in photograph Xo. 2 in the same number. These dark 

 regions are also well shown in the photograph published 

 in the May number for 1890. 



Though no doubt the greater number of terrestrial 

 volcanoes are adjacent to the sea, some, as those between 

 Siberia and Thibet, and in the Chinese province of Man- 

 chouria, as well as the extinct volcanoes of central France, 

 are at a considerable distance from the sea or lakes. Mr. 

 Scrope long ago pointed out that though a considerable 

 amount of steam escapes from active volcanoes, it does not 

 follow that the water producing it was originally derived 

 from the sea. All rocks contain a considerable amount of 

 water of crystallization, and we are probably not warranted 

 in saying that a volcanic irruption could not take place 

 without the presence of an adjacent sea, lake, or river. 



Though I do not think that the albedo of the lunar sur- 

 face has been determined with the accuracy which Zollner 

 supposed, it seems to me that we have evidence that the 

 whiter portions of the lunar surface are very white com- 

 pared with any terrestrial rocks, and that it is more 

 probable that the lunar mountains are capped with snow 

 than that the higher regions are formed of very white 

 rocks, while the valleys and low-lying regions are always 

 formed of much darker material. I therefore agree with 

 Mr. Peal as to a large portion of the lunar surface being 

 covered with ice or snow, but it is easier to me to account 

 for the great ring formations, as being analogues to terres- 

 trial volcanoes, than to suppose that they are rings of ice 

 and glacial phenomena of which we have no terrestrial 

 analogues. — A. C. Eanyard.^ 



THE CORONA OF THE SUN AND STARS. 

 To the Editor of Knowledge. 



De.ar Sir, — Although the teachings of modern astro- 

 nomy have led us to look upon many of the fixed stars 

 as veritable suns, merely reduced by their vast distance to 

 a subordinate lustre, the possibility of being able to 

 observe the corona about stars seems to have escaped 

 notice. 



Diirmg the last seven years, the principal work of this 

 observatory has been the observation of a number of long 

 period variable stars, which decrease in lustre from about 

 the 5th to below the 13th magnitude, in periods rangin" 

 from 200 to 600 days. They differ in a remarkable 

 manner from the ordinary fixed stars. Most of them are 

 of a deep red or ruddy colour, and many are more or less 

 nebulous ; they may be divided into four classes, viz., stars 

 having 



{a) A remarkably well-defined, almost planetary, disc ; 



(6) Well-defined stars surroimded by a more or less 

 dense, ruddy atmosphere ; 



