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November lo, 1904] NATURE 



ing a meteoric spectacle on perhaps a more extensive scale 

 will probably be revived on the near approach of the Leonid 

 epoch ot 1904. Reasons have already been given for sup- 

 posing that last year's display was connected by the nine- 

 teen years' period with a very similar phenomenon observed 

 on November 13, 1865, the interval between the two events 

 representing two complete revolutions of the meteoric cycle. 

 The present epoch, therefore, which is thus associated with 

 the historic meteor shower of November 14, iSOb, will be 

 liable to reproduce its brilliant pro'lotype, though only to a 

 limited extent. 



. The anticipated shower, however, if it takes place, will 

 not occur on the night of November 14, as it might naturally 

 have been expected to do, owing to 1904 being a leap year. 

 The meteor-swarm, according to calculations made by the 

 present writer, has undergone considerable retardation since 

 igoj, and as a result of this perturbation the Leonid meteor 

 shower becomes due in 1904 on the night of November 15. 

 It is on the latter night, therefore, that the maximum will 

 take place, whether it culminate in a shower or not. There 

 will occur, however, on November 14, ish., an interesting 

 miniature meteor display. The shower on the night of 

 November 15, though not so intense, will be more extensive 

 than that of 1866, as maxima fall due at gh., i2h. to ish., 

 and i7h. 30m. G.M.T. John R. Henry. 



The Definition of Entropy. 



From time to time controversies have appeared in various 

 journals regarding that most difficult of all physical con- 

 ceptions — entropy. I have purposely avoided passing any 

 opinions as to the merits of the views of different writers, as 

 I have considered the question far too large a one to be 

 dealt with satisfactorily by destructive criticism directed 

 towards particular points. I have, however, now found a 

 definition of entropy which certainly appears to meet most 

 of the objections to the conventional treatment. That 

 definition may be stated somewhat as follows ; — 



Let the available energy of any system at any instant 

 relative to a refrigerator of temperature T„ be defined by 

 the condition that it is the maximum amount of energy 

 that could be obtained from the system at that instant by 

 reversible thermodynamic engines working between the 

 system and the refrigerator Tj, the remaining portion of 

 the energy being, of course, called non-available energy. 

 Then in any change of the system the increase of entropy 

 is the quantity obtained by dividing the increase of non- 

 available energy by the temperature T„ of the refrigerator. 



I hope to publish a detailed treatment shortly, but in the 

 meantime I would mention that this definition overcomes 

 all the difficulties inherent in the conventional treatment of 

 at least the more ordinary irreversible phenomena, such as 

 friction, impact, gas rushing into a vacuum. 



If we adopt the principle of degradation of energy as the 

 fundamental second law of thermodynamics (as I suggested 

 in the Boltzmann Festschrift), Clausius's statement that the 

 entropy of the universe tends to a maximum now follows 

 at once. So. too, do his inequalities. For everv irreversible 

 transformation in the interior of a system produces loss of 

 available energy, and therefore (since it does not affect the 

 total energy) increase of non-available energy, and there- 

 fore increase of entropy. We may say that entropy can be 

 generated, but never destroyed. It follows that the total 

 increase of entropy in the system is greater than the quantity 

 of entropy entering from without. This is Clausius's in- 

 equality for an irreversible non-cyclic process. If the process 

 is cyclic the total gain of entropy is zero, and therefore the 

 entropy generated in the system must be exported during 

 the cycle. This is Clausius's inequality for a cyclic process. 



The introduction of the refrigerator presents no real 

 difficulty. If non-available energy, instead of being given 

 to the refrigerator T„, is worked down reversibly to a re- 

 frigerator at a lower temperature T,, its amount will be 

 decreased in the ratio T, : T„. G. H. Brv.\n. 



The Direction of the Spiral in the Petals of 

 Selenipedium. 



In Selenipedium grandc, S. longiJoUinu, and 5. conchi- 

 feriim, the twisted petals are so arranged that the direction 

 of the spiral is right-handed on each side. 



They are not heteronymous, i.e. the right petal with a 

 left twist and the left petal with a right twist, as in all 



NO. 1828, VOL. 71] 



antelopes' horns, nor are they arranged homonymously, a? 

 in most sheep's horns,' but the twisted petals have the same 

 direction on each side, and in the cases above mentioned 

 the right-handed spiral is always present. In trying to 

 find a cause for the direction, I expected it to appear that 

 before and during the unfolding of the flower the petals 

 were twisted when lying together, and thus took the bias, 

 which continued during growth. If two strips of paper 

 be laid together and twisted into a pipe-lighter, each, when 

 separated, would exhibit the same spiral twist. 



Examination of the still-folded flower proves that this 

 simple explanation is not the true one, and, at least in 

 5. grande, the petals are straight when they show at first 

 (two inches or more in length), and become afterwards 

 spirally twisted during growth and elongation. 



The necessary bias to determine the direction of the spiral! 

 evidently acts after the unfolding of the flower, and is a 

 slight force acting continuously during growth, such as 

 would be made by the circulation if there were a difference 

 in the circulation of the sap in the two edges of each petal. 



This difference would act alike in each, and would make 

 each petal twist in the same way ; but, of course, this is a 

 mere conjectural suggestion. George Wherry. 



Cambridge, October 30. 



Thinking Cats. 



The story of the cat that saved the cook, in your last issue, 

 is certainly remarkable, but surely it is not unusual for 

 cats to find out how to direct attention when they want to 

 get into or out of a house, or for them to conceal their 

 kittens in curious places. 



Two instances of the former occur to me among many. 

 .\ cat in my father's house used to rattle the letter-plate at 

 the front door (it was in a window near the door) whenever 

 it was shut out, and another, in my own house, would come 

 to any lighted window, even on the top storey, and tap at 

 the glass if it was shut out at night. In the same house a 

 cat hid its kittens, after one family had been destroyed, 

 under the boards of a lead flat, so that, as they grew, it could 

 not get them out, and directed our attention to them by 

 running backwards and forwards. They were released by 

 taking up the boards. 



From cats to birds seems a natural transition. I have a 

 curious instance, at this moment, of a pair of robins mis- 

 taking their own importance. Last spring they built, and 

 reared their family, in a hole in the wall of an old country 

 mansion, which was being rebuilt under my supervision. 

 The wall was inside the house, in the great hall, and the 

 female sat on her nest, looking out at the workmen, amid 

 all the noise and disturbance of building. They disappeared 

 in the summer, but now that the house is finished and 

 occupied, the pair have returned, and flit about the same 

 hall and the adjoining drawing-room, evidently under the 

 impression that the house was built for them. 



R. Langtox Cole. 



Change in the Colour of Moss Agate. 



.\ friend of mine possesses a penholder the handle of 

 which is made of moss agate. Originally the colour of the 

 handle was bluish throughout, but recently the upper part 

 of the handle has become very much lighter in colour and 

 much more transparent. 



I thought perhaps some of your readers could tell me 

 whether it is usual for moss agates to undergo changes of 

 this kind after having been cut and polished, and, if it is 

 usual, to what agent or agents the change is ascribed. 



W. .\. Whitton. 



County School, Bridgend, November 7. 



The Origin of Life. 



Mr. Hookham ingeniously argues that experiments to 

 evolve living out of non-living matter are inconclusive and 

 nmst probably always fail because the sterilising agent 

 used, which is commonly heat, " eliminates not only life, 

 but its potentiality at one stroke." 



Most of us believe that the earth was at one time an in- 

 candescent globe. Neither life nor the potentiality of life 

 could have existed in such circumstances. How would Mr. 

 Hookham, on the theory of evolution, explain their first 

 introduction? Geologist. 



1 Na 



FE, December 12, 1901 ; Lancet, January : 



