142 



NATURE 



[Jtine 6, 1878 



The Virial in Thermodynamics 



In my letter on the Virial in Nature, vol. xviii. p. 39, a line 

 of the description of a force's " radiancy " (as it was there termed) 

 with respect to a given point was accidentally omitted ; and the 

 definition should have been the product of the distance of its 

 point of application from the given point or " focus," and the 

 resolved part of the force in the direction of that distance, the 

 last and most important member of which product was unmen- 

 tioned by some unintentional oversight in the description. It 

 would also be wrong, in the dynamical equation of the virial, the 

 vis viva and the radiancy of momentum of a system to range the 

 vis viva and virial together (as I did in the letter) in the class of 

 physical agents, bound therefore by known laws of conservation, 

 since either their joint or their separate effects in changing the 

 system's total radiancy of momentum are easily seen, if we sup- 

 pose one of them, for example, the vis viva, to act alone, to be 

 totally unfettered, and therefore their actions to be of a measur- 

 able kind, but not subject, like that of natural agents, to any known 

 laws of physical connection. 



The rate of acceleration of a fourth part ^ of the triple sum 

 formed of a system's moments of inertia round any three axes 

 at right angles to each other is the rate of change of its total 

 radiancy of momentum, and if the various parts of the system are 

 all moving uniformly in straight lines, their joint vis viva measures 

 the rate of this change ; but it cannot be said to cause or pro- 

 duce it, since, by the laws of motion, the bodies unassisted or 

 left to themselves will continue to produce, by their vis viva, 

 the same rate of change, without connection in doing so, with 

 any known physical agent, from whose class, accordingly, it is 

 evident that both vis viva and the "virial," or the radiances of 

 a system's forces as linked in an equation with acceleration of 

 total moment of inertia, are formally excluded. The equation 

 has very important applications : as when, on an average of a 

 sensible time, the total moment of inertia remains unaltered, or 

 when a system is apparently at rest : for example, in the case of 

 immobihty of a gravitating atmosphere in a state of eqailibrium, 

 under any possible assigned law of variation of temperature. 

 But the idea of this state of immobility being a necessary one, 

 which the vis viva and virial together of the ponderable mass is 

 constrained to conserve — placing them together in a fixed and 

 definite relationship to each other, or to any other agents of 

 physical phenomena, subject to known laws of conservation — 

 was evidently a totally mistaken and unreal one. 



A. S. Herschel 



The Meteor of May 12 



In Nature (vol. xviii. p. 105) the statement occurs among the 

 "Notes" that the brilliant bolide of May 12 was seen at 

 Geneva, the local time being said to agree. May I call your 

 attention to the fact that the difference between Greenwich and 

 Geneva is 25 minutes (or 2 minutes more if Berne time is com- 

 pared). Thus 9.45 is 9.20 Greenwich time, nearly half an 

 hour after the meteor recorded by English observers. It is 

 now a well recognised fact that large meteors come in groups, 

 naturally raising the suggestion that such groups form part of a 

 slowly disintegrating mass. 



Fi-om records I have obtained from Scarborough, Leeds, and 

 Bradford, combined with an excellent observation of the latter 

 part here, and the notices contained in your number for May 16, 

 I find the probable positions of beginning and end to be from 

 4 miles west of Northallerton to 5 miles west of Hawick, a 

 distance of 94 miles, the angle of flight being 38° with the horizon, 

 making an actual com'se of 108 miles described in about 9 seconds, 

 giving the unusually slow rate of 12 miles per second. This, 

 and one or two other points, make it possible that the course 

 really extended further. But the end was in nearly all instances 

 obscured by clouds and the observations in line with the meteor's 

 course. An exact description of its course by your Edinburgh 

 correspondent (especially as to whether it passed near the zenith) 

 would make this certain. 



May I venture to make one or two suggestions to your corre- 

 spondents who favom- you with notes on meteors ? When, 

 for any reason, celestial measurements cannot be given, rough 

 measurements of the positions made either by holding a ruler in 

 front of you, or, if light allows, by the minutes upon a watch 



I The acceleration of the total moment instead of the fourth part of the 

 total moment of inertia was wrongly written in the postscript of my letter as 

 equal to__ the rate of change of momentum-radiancy. Actual energy and 



vmai, as defined by Clausius, are also half of the quantities here described 

 as VIS viva, and radiancv of a force. 



lace, \\hich shall enable the actual height, and distances from a 

 point of the compass to be determined, are by far the most 

 valuable items, accompanied of course by exact time, date, and 

 place. Thus a meteor might appear at a height of 15 inches on 

 a base 27" (an arm's length) and 12" W. of north. Oi", having 

 placed 12 o'clock level, the hand at 10 minutes past might point 

 to the place of disappearance, an angle of 7 minutes (42°) giving 

 the distance E. of south. Prof. Herschel, of Newcastle, gives 

 some capital hints in a letter published in the Scotsman, May i, 

 upon the March daylight meteor. Either he or Capt. G. L. 

 Tupman (or I myself) would at any time be glad of observations, 

 in which case a rough plan, indicating its position among the 

 stars, would be of great value. The position of the meteor with 

 reference to houses, trees, &c., the course across a window, if 

 seen indoors (the observer's position and distance being also given 

 and the points of the compass), and many similar items are very 

 useful for after reference and maylead to very exact determina- 

 tio"^- " J. Edmund Clark 



20, Bootham, York, May 28 



"Divide et Impera" 



Verily we have divided and subdivided, and as yet are but 

 little nearer the "conamand" promised. 



I am a subscriber to your able magazine, which is extensively 

 read in South America, and beg to bring the following subject 

 to the notice of your zoological readers : — 



At this distance of 8,000 miles and at the outskirts of civilisa- 

 tion, books of reference are scarce, or, if existing, difficult ot 

 access. In constructing some zoological tables I am constantly 

 beset by the difficulty of discovering two, three, four, five, six, 

 or more synonyms for the same species, or in the case of a sup- 

 posed new species find afterwards that the same animal has been 

 described under another name ; the genera often differ ! the 

 families constantly vary, and even the higher classification is by 

 no means constant. 



Where is all this perpetual confusion to end ? In the science 

 being destroyed by excessive or faulty nomenclature ? We want 

 an Ariadne with her thread to lead us out of the maze, for such 

 it is, especially to young zoologists like myself. 



Is it too much to expect that an international zoological con- 

 gress should be constituted with power to methodise and reduce 

 to order this chaotic classification, and print and publish autho- 

 rised lists of fauna? How are young naturalists to progress, 

 constantly hindered as they are by wasting weaiy hours in 

 seeking for that which should be patent at a glance ? 



Such a congress should, by unanimous consent of the chief 

 zoological societies of Europe, fix immutably not only the supe- 

 rior classification, but also the generic and specific nomenclature ; 

 and in the event of new species being discovered, whilst con- 

 ceding the right to the discoverer and describer to affix its title, 

 this should in all cases be subject to the approval of the Inter- 

 national Congress, which might sit permanently in the shape of 

 one or two deputies. 



It seems to me the science has already emerged from its 

 swaddling clothes, and it is high time for om: scientific authori- 

 ties to give up that fatal habit of generating and clinging to their 

 own superstitions, and fostering that intense jealousy so charac- 

 teristic of them, which, leading to multiplicity of systems, leads 

 only to distraction. 



There may be aberrant forms yet undecided (there will be 

 such, perhaps, to the end of time) ; borderlands to be limited ; 

 yet there is ample material to fix unalterably and universally the 

 skeleton of that science, to fill in whose details there are multi- 

 tudes of willing and skilled hands, ready to aid, in all parts of 

 the world. E. W. White 



Buenos Ayres, May i 



A Quadruple Rainbow 



In the afternoon of Friday, the 24th ult., while proceeding 

 by rail to Dublin, and before reaching Abbeyleix station, I 

 observed the curious phenomenon of four rainbows forming a 

 single bow — that is, without any dark space intervening between 

 the colours. The four bows were all of the same, or nearly the 

 same, breadth, but I cannot say whether all the colours were 

 present in each. 



The brighter colours — as the red and yellow — showed that 

 the bows were arranged in the same order. 



I called the attention of several other passengers to the novel 

 spectacle. 



