38 



KNOWLEDGE. 



[Febbuaey 1, 1900. 



indabitable marks of a much more recent origin. First 

 of all, as already pointed out, the astrological signs of 

 the Zodiac have nothing to do with the actual stars ; 

 the constellations to which they owe their names are 

 left quite out of sight and ai"e almost foi-gotten. 

 Next, and most significantly, we find that Ai-ies 

 is the primitive sign of the Astrological scheme. 

 There is no hint that it ever had been Taurus. 

 This fact would of itself sufiice to show that Asti-ology, 

 at any rate in any such systematised form as we now 

 know it, is far younger than Astronomy, younger by 

 the time which precession takes to cross an entire sign 

 of the Zodiac, younger, that is to say, by a period 

 which wo may roughly put as 2000 years. No doubt 

 sun-worship and moon-worship reach back almost to 

 the birth of the human race ; no doubt eclipses, comets 

 and meteor-showers struck terror into men from the 

 earliest ages, and many superstitions and fancies of an 

 astrological tendency took fomi and shape in primitive 

 times and prepared men's minds to accept the im- 

 posture when at length it had attained an organised 

 development ; but we can say positively that Astrology 

 in anything like a complete system cannot date back 

 earlier than 1800 B.C., when the sun first entered Aries 

 at the Spring Equinox, and that it must almost cer- 

 tainlj' have arisen many centuries later. 



[The Editors do not hold themselveB responsible for the opinioDs or 

 statements of correspondents.] 



IS THE UNIVERSE FINITE ? 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — Of course the academical question, whether 

 the Universe is finite or infinite, is not likely to be 

 solved in our time, and I do not think that the difii- 

 culties raised by some correspondents of your journal, 

 and elsewhere, about our idea or conception of the 

 infinite will afford us the least assistance in arriving 

 at the solution. The structure of the Universe is a 

 verv different thing from our ideas or concejjtions 

 of it. 



But the question which occnrred to Mr. Burns, and 

 had previoush' occurred to others, is in reality a differ- 

 ent one. It is this : Is the Universe confined within 

 limits which we mav reasonably expect to ascertain and 

 define — for instance, within a sphere with the sun (or 

 earth) as centre, and a radius equal to 100,000,000 

 times the sun's distance from the earth ? In fact a 

 sphere with a considerablv smaller radius than this 

 would account for everything that we at present know. 

 But although this explanation is admissible, there ar3 

 grounds for doubting whether it is the true one. 



Mr. Anderson, I think, falls into a vei-y common error 

 on this subject, by supposing that nothing can affect 

 the eye unless it can be separately seen. The current 

 theory at present is that Saturn's rings consist of 

 meteors. 'What would be thought of an astronomer 

 who contended that the ring must be invisible because 

 the meteors cannot be separately seen ? Again : look 

 at the Milky Way on a clear, moonless night. It is 

 perfectly visible to the naked eye ; but can it be said 

 that our most poverful telescopes, whether used by 

 the eve or on the photographic plate, have as yet re- 

 solved all this luminosity into separately visible stars? 

 The zodiacal light and the Gegenschien may be cited 

 in further illustration of this. Stai-s or other objects, 

 which no one has as yet succeeded in rendering 



separately visible, do unquestionably affect the naked 

 eye ; and if we find that the general illumination of the 

 sky falls much short of what it ought to be on any 

 given theory, we cannot explain this fact by supposing 

 that stars of less than a given magnitude produce no 

 effect at all. Take a single meteor at the distance of 

 Saturn and of the average size of those which compose 

 the rings ; regard this meteor as a star, and of what 

 magnitude will it be? 



Bright stars lose as much by absorption, atmospheric 

 or telescopic, as fainter ones. Hence, we may neglect 

 the element of absoi-ption when dealing with the total 

 light of stars of different magnitudes. It is, of course 

 true that " if the illuminating area were to decrease, 

 owing to increase of distance, more rapidly than it in- 

 creased owing to greater numbers. . . it would never give 

 us a blazing sky," as Mr. Hill says. But this could not 

 occur without a constant thinning out of the stars as 

 we pass to greater distances from the solar system. On 

 the hypothesis of unifoi-m distribution, when the light 

 of the stars decreased in the proportion of 2.512 to 1 

 (one magnitude) the number would increase in the pro- 

 portion of 3.984 to 1, and the total " illuminating 

 area" would be more than li times as great as before. 

 Mr. Burns, I apprehend, did not seek to prove that the 

 stars could not extend to infinity. What he sought to 

 prove was that they could not do so unless there was a 

 constant thinning-out on the way. The question is 

 almost equivalent to this : Is the sun a member of a 

 star-cluster ? 



Admitting, however, that the sun is a member of a 

 cluster, the chances are that it is not in the centre 

 of the cluster ; and, if so, this thinning out of the stars 

 ought not to take place at once. But if we take in the 

 entire sky, as far as I can judge, the apparent thinning- 

 out begins almost at once. Hence the existence of an 

 absorptive medium of some kind in space is naturally 



suggested. 



W, H, S. MoNCK. 



LUNAR SEAS. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — I hope Mr. Tepper's very thoughtful paper 

 and Mr, Tappenden's letter in your last issue will 

 revive an interest amongst your readers in the study 

 of lunar cosmogony. 



The theoi-y suggested by Mr. Tepper has so many 

 things in its favour that I cannot think it unimportant ; 

 the fall of meteors on its surface, where no atmosphere 

 exists, certainly suggests a plausible origin for the rays 

 from Tycho and other ring craters as we call them. I 

 am not sure but some of the craters themselves may 

 have originated by the fall of large meteors coming 

 down vertically into a deep coating of such dust as Mr, 

 Tepper speaks of, and might explain the radiating rays, 

 whilst meteors moving obliquely would explain the rays 

 which run parallel to each other, and there are many 

 such. 



The large plates of the French photographs by Loewy 

 and Puiseux will be of very great value in the study of 

 lunar questions; the part of one of these published in 

 December Knowledge shows many impoi-tant points, 

 which answers some of the suggestions. The ray below 

 Bullialdus (E) does not ran into the crater Tycho but 

 passes close to its eastern wall, and can be traced run- 

 ning in the same direction on the other side, and we can 

 easdy trace another ray running parallel to it farther 

 east, as if a meteor had ploughed through some loose 

 matter, forming a furrow and throwing the material on 



