Deoembee, 1903.] 



KNOWLEDGE 



279 



extremely sensitive to the colour of their close surroundings 

 that if they be moved from a dark stem to a piece of lichen, 

 for instance, and nothing else be given them to rest on 

 (neither of them rest on their food-plant), they will, like 

 the chameleon, in a few days change their pattern from 

 dark to speckled, and be again invisible. 



May not this colour sensitiveness in certain individuals 

 be responsible for much that is put down to natural 

 selection, and account for the many glaring failures that 

 occur in the principle of protective resemblance ? 



Royal Societies Club, Jos. F. Green. 



12th November, 1903. 



MOCK-SUNS. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs,- — Colonel Mark wick gives (p. 231) such a descrip- 

 tion of mock-suns that it seems needless to add more, 

 beyond saying that they are caused by refraction from 

 ice-prisms ; and also that the clouds on which they appear 

 may be so thin as to be imperceptible otherwise, and yet 

 capable of producing bright mock-suns, as seems to have 

 been the case on the occasion mentioned by Lieutenant 

 K. D. Field (p. 206). 



Sunderland, T. W. Backhouse. 



21st October, 1903. 



IS THE UNIVERSE FINITE? 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, —Dr. Wallace's new book will no doubt renew the 

 controversy on this question. I therefore ask space for 

 some considerations as to the consequences of the finite- 

 ness of the Universe which do not seem to be sufficiently 

 recognised. 



If the Universe consists of a finite number of finite 

 bodies I apprehend that it must have had a beginning in 

 time, which drives us back to creation a nihilo. Take, for 

 example, the Meteoritic theory, or that of Professor 

 Bickerton. All heat — at least all intense heat — is the 

 result of collision. But in all collision motion (molar 

 motion) is destroyed, and in fact the amount of motion 

 destroyed is proportional to the amount of heat developed. 

 A finite Universe is only capable of containing a limited 

 amount of motion or motive energy — for I suppose it will 

 be admitted that the velocities with which bodies originally 

 moved were not infinite. How, then, if matter has existed 

 from eternity a iiarte ante, is there any motit)u still left — 

 how is it that all bodies are not now collected in a single 

 motionless mass ? It is true that there are decreasing 

 series, the sum of which will always be finite, although 

 the series is carried to infinity. But the explanation of 

 this fact is that after a very large number of terms the 

 amount of each succeeding term becomes so minute as to 

 be negligible. No advocate of Meteoritic or Collisicmal 

 theories will admit that collisions have now attained this 

 utter insignificance. Indeed it is maintained that they 

 still occur on a large scale and produce very sensible effects, 

 and this not at long intervals of time but constantly. 

 Creation a nihito, or the transformation into matter of 

 something which in its original condition was quite unlike 

 matter, seem to be the only alternatives. 



The Nebular theory leads to a similar result. The great 

 agent is here the radiation of heat into space, owng to 

 which the nebula contracts until it becomes solid, becoming 

 by a rather paradoxical law hotter as it loses heat. But 

 if this process has been going on from eternity a parte 

 ante in a finite Universe — the original nebula or nebula^ of 

 course containing a finite quantity of heat or motion con- 

 vertible into heat, how could there be any nebultc left at 



the present day ? But I need say nothing as to their 

 actual number, and there is reason to think that besides 

 those known to us there are vast numbers of them 

 giving little or no light, the contracting process not 

 having as yet jsroceeded far enotigh to render them self- 

 luminous. Any other theory that I know of leads to a 

 similar result. A finite Universe must ultimately reach a 

 stage at which further changes are impossible unless it is 

 so constituted that the series of changes will return in 

 cycles — which is also impossible if it is constantly losing 

 heat without any return. 



I have never seen the proof of Lane's law with regard 

 to the contraction of gases, but I should be glad if any of 

 your readers could tell me whether according to it the 

 radiation of heat from a gaseous body increases or 

 diminishes while it is contracting. The increased tem- 

 perature implies greater radiation from each square foot of 

 the surface, but the contraction implies that the number 

 of square feet in the surface is diminishing. Which of 

 these causes is the more potent? If the latter, contraction 

 due to the loss of heat can never increase the total radia- 

 tion of heat from the contracting body. The shape of the 

 body is, I presume, to be unaltered by the contraction. 



I desire to correct one portion of my former letters. 

 The comparisons between the light of the full moon and 

 that of the sun were, I believe, made between the full moon 

 and the hemisphei'e of the sun turned towards us, and not 

 the light of both hemispheres as I had supposed. Hence 

 all my figures should have been doubled, by which my 

 argument is strengthened. 



W. H. S. MoNCK. 



ON RESOLVING THE GASEOUS MOLECULE 

 AND SEEING IT. 



TO THE EDITORS OF KNOWLEDGE. 



SiES, — I think the following will greatly interest your 

 readers. Fill a thin flask with dry pure chlorine gas and 

 a small quantity of dry air. Illuminate the gases with 

 the light from the electric arc lamp, concentrated as much 

 as possible. The gaseous molecules are distinctly visible 

 with the naked eye. They are very small spheres of 

 equal dimensions. 



West Dulwich, S.E., Fkedk. Hovenden. 



October 26th, 1903. 



GASEOUS NEBUL.'E. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — The idea has occurred to me that possibly the 

 phosjihorescent glow of the gaseous nebulae may be due to 

 the presence of radium in the gaseous state ; in other 

 words, that the unknown element " nebuliiun " may be 

 identical with radium. Has the spectrum of radium been 

 well determined, and, if so, does its spectrum contain a line 

 near that of " the chief nebular line " at A 5005 ? 



J. E. Gore. 



Dublin, 1903, October 25th. 



Astronomical. — Valuable additions to our knowledge 

 of the phenomena of new stars ai'e resulting from investi- 

 gations at the Lick Observatory which are being made 

 with the instrument specially designed for very faint 

 objects. It has previously beeu found that Nova Cygni 

 (1876) now exhibits no bright lines, and it is now stated 

 that Nova Auriga* (1892) is approaching the same con- 

 dition, the chief nebular line having disappeared and other 

 bright lines having become weaker in proportion to the 



