June 8, 1883.] 



♦ KNOWLEDGE ♦ 



335 



L 



MAGAZINE OF^GIENCE 



PL AlNlYiyORDED -£XAC AdESCRIBED j 



LONDON: FRIDAY, JUNE 8, 1883. 



Contents op No. 84. 



FJIGB 



Lunar Lessons. By R. A. Proctor 335 

 A Xttturaliat's Year. XIV. AmoDt; 



thi-Gnwses. Bv Grant Allen 336 



The Fisheries feihibition. By 



John Ernest Adj 337 



Professor Hughes' on Mn^etism. 



BtW. Slinao 339 



Law's of Brii:htness. III. {Iltut.) 



By K. A. Proctor 3« 



Cremation 3-11 



The Chemistry of Cookery. XI. 



By W. Mattien WiUiama. (/»u>.) 311 



Editorial Gossip 343 



Reviews : The Past of our Earth— 

 Ortjanie Chemistry — European 

 Mineral Waters — Poems for 



Penny Readings 311 



The Face of the Sky. By F.R.A.S. 346 

 Correspondence; Singular Solar Phe- 

 nomenon — Stays and Health- 

 Rational Dress— A few Observa- 

 tions on Hoat, Ac, 4c- 316 



Our Mathematical Column 318 



Our Chesa Colonm 319 



LUNAR LESSONS. 



By Richard A. Proctor. 



I^HE more the moon is studied, the clearer seems to be 

 the evidence that she gives respecting the life history 

 of a planet. She tells us more, perhaps, of the future of 

 our earth than of the past ; but she tells us of the past 

 too. That the moon is waterless and practically airless 

 too, now, is certain, and, therefore, there is probably no 

 life now on her surface, though for those who like such 

 fancies the belief is always open that there may be 

 creatures on the moon utterly unlike any with which 

 we are acquainted on earth. Yet the moon's face tells 

 us of a remote youth — a time of fiery activity, when 

 volcanic action even more effective (though not probably 

 more energetic) than any which has ever taken place 

 on this globe, upheaved the moon's crust. But so 

 soon as we consider carefully the features of her 

 surface we see that there must have been three 

 well marked eras of vulcanian activity. Look at the 

 multitudinous craters, for e.xample, around the Metropolitan 

 Crater (as Webb has happily named it) Tycho. They tell 

 us of century after century of volcanic disturbance — but 

 they tell us more. They mark a surface which varies in 

 texture, and therefore in light^reflccting power in such a 

 way as to show that the variations were produced long 

 Jjefore the \olcanic action began by which the craters 

 were formed. For the variations of texture are such as 

 to mark a series of streaks — some of them two or three 

 thousand miles in length, and many miles in breadth, 

 extending radially from Tycho. Craters lie indifferently 

 on these brighter streaks and on the intervening 

 darker spaces, and some craters can be seen which 

 lie right across a bright streak with parts of their ring 

 on the darker regions on both sides of the streak. Of 

 course, this proves that the craters were formed long 

 after the great streaks. When the streaked surface was 

 formed, it must have been tolerably smooth ; for we see 

 the streaks best under a full illumination, and there is no 

 sign of any difference of elevation between them and the 

 darker ground all around ; they are neither long ridges nor 

 long valleys, but mere surface markings. Yet must they 

 have been formed by mighty vulcanian disturbance, such, 



indeed, as we may be certain went on at the early stage of 

 the moon's history, to which these radiating .streaks must be 

 referred. It seems clear that, as Nasmith has illustrated 

 by experiment, they belong to that stage of the moon's 

 history when her still hot and plastic crust parted with its 

 heat more rapidly than the nucleus of the planet, and so, 

 contracting more quickly, was rent by the resistance of 

 the internal matter, which, still hot and molten, flowed 

 into the rents, and spreading formed the long broad 

 streaks of brighter surface. It seems as clear that the 

 next stage of the moon's history (after many thousands, 

 perhaps millions, of years had passed) was one in which 

 the cooled crust, still plastic, contracted little, while the 

 still hot nucleus contracted steadily, so shrinking from the 

 crust, which, under the action of gravity, closed in upon 

 the nucleus in such sort as to a form a wrinkled or corru- 

 gated surface. This was the second era of lunar vulcanian 

 disturbance. The third was the era of great volcanic 

 eruptions, during which the mighty craters were formed 

 which are so numerous on the lighter tinted higher regions 

 of the moon's surface. Were there no seas or oceans on 

 the moon at this time 1 It is strange if there were none, 

 when we consider the connection which exists on the earth 

 between the activity of the great volcanic vents and the 

 pro.ximity of water. It is stranger still if we consider that 

 those regions where, if water had ever existed on the moon, 

 it would have formed seas, are without exception charac- 

 terised by a different tint, and a different surface contour, 

 from what we find in the regions which would in that case 

 have formed the lunar continents. All the lower levels 

 are dark, are much more uniform, and are marked by few 

 craters, and those small. This is no mere accident or 

 coincidence. It is a feature which we are justified in 

 regarding as characteristic ; and, so regarded, it seems to 

 force upon us the conclusion that those lower levels are in 

 reality old sea-floors, formed in a different way from the 

 higher levels, and therefore presenting a different tint and 

 reflecting a different amount of light. 



When we thus recognise in the moon the three stages of 

 past vulcanian energy which Mallet and Dana have recog- 

 nised (though the evidence has not been quite so obvious) 

 on the earth, and the signs also of a past fitness for the 

 support of life, seeing that the presence of seas implies 

 also the presence of an atmosphere dense enough to make 

 the boiling-point of water not too low, we recognise the 

 significance of the evidence which the moon gives re- 

 specting the earth's future. What has happened to her 

 will happen also to our earth, though doubtless with 

 variations in details corresponding to different conditions. 



Yet science has good reason for regarding as exceedingly 

 remote the time when the earth will be at the stage of 

 planetary development which the moon has reached. If 

 the earth's crust, God's work, whose teachings, therefore, 

 if we can but read them aright, are God's words, speaks 

 truly, it is certain that tens of millions of years have 

 passed since even that stage of the earth's life through 

 which she is now passing began. But suppose, for the 

 sake of argument, we put twelve million years only as the 

 time which has elapsed since the earth and moon were at 

 the same (necessarily much earlier) stage of planetary life. 

 The earth's mass exceeds the moon's 81 times, and there- 

 fore at that time she had 81 times as much heat to part 

 with as the moon. But her surface is now (and the pro- 

 portion cannot have been very different then) only some 

 1 .3 .\ times greater than the moon's. Thus, since 81 con- 

 tains 13.1 six times, the earth has parted with her heat at 

 only one-sixth of the rate which would have made the 

 supply last just as long as the moon's. Each stage of the 

 earth's cooling, or of the earth's life, has been six times as 



