December 14, 1893] 



NATURE 



149 



(as in chemistry, for the increasing oxidation results, &c. ), the 

 coinage of words as fresh needs arose would proceed automxti- 

 cally on rational lines. 



This might very well form the object of a special committee 

 of the British Association. 



Mr. Oliver Heaviside's system for electromagnetic matters 

 has much to recommend itself for adoption, also, in general 

 physics. 



For example, after the plan (i) conduc/ZiJ/^ (2) con^wztance, 

 (3) conduc/zV//)', we would have, in the case of radiant energy, 

 (i) radia//f«, (2) radia/a;/a, (3) radia^/z'/Zr. 



The first is tor reference in a general way to the phenomenon 

 in question ; the second refers to i's amount in appropriate 

 uniis in any individual case ; while the third is suitable for 

 expressing the piculiar action or factor in the phenomenon 

 possessed by different kinds of bodies. Thus the radiafaiice 

 from a hot kettle would be the total quantity of energy lost per 

 second. The radia/zz'/Aj/ would be the quantity of this ^per 

 square centimetre. 



With a view of examining the feasibility of this system, the 

 following list is subjoined. Many of the words appear at first 

 as if tliey would prove most awkward in practice, but 

 remembering similar fears (which subsequently proved ground- 

 less) in electromagnetic matters, one is afraid to say they are 

 due to more than unfamiliarity. 



Special attention deserves to be called to inertance as a 

 good name for mass, and inertivity for density, to rotatance 

 lor moment of momentum, and rotativity for moment of inertia. 



Geo. Eras. Fitzgerald. 

 Fred. T. Trouton. 

 Physical Laboratory, Trinity College, Dublin, 

 December 5. 



On the Nomenclature for Radiant Energy. 



In connection with this subject there are many things to be 

 considered, and one of the most important is the question of 

 ladialion and absorption, which requires a completely new 

 nomenclature to get over very serious ambiguities that at pre- 

 sent embarrass the subject. It is very necessary to distinguish 

 between what may be called, on Prevost's theory of exchanges, 

 the total radiatance from the actually observed loss of energy 

 by radiation which is, according to this theory, the difference 

 bttween the total radiatance and the total absorbance. This 

 difference per degree of temperature is very commonly called 

 the radiating power, but this same word is used in quite a 

 difi'erent sense when it is attempted to prove, from Prevost's 

 theory of exchanges, that the radiating is equal to the absorbing 

 powers by a consideration of thermal equilibrium. In this 

 latter case the term radiating power means obviously the total 

 radiatance of Prevost's theory. 



It may also be worth while calling attention to the theory, 

 given at Nottingham by Lord Rayleigh, as to the absorbivity of 

 lough surfaces being equal to unity. The general idea under- 

 lying his investigation is that owing to diffraction the waves 

 amongst the deep corrugations in the surface spread abroad 

 within them, and hardly any of their energy escapes out again. 

 At the time 1 called his attention to the way a similar theory 

 would explain the radiating power of rough surfaces, as I have 



NO. 1259, VOL. 49] 



taught here for years back. I am mentioning this now to call 

 attention to an experiment of Magnus' mentioned in Jamin 

 (" Cours de Physique," vol. iii. part 3, p. 113, top line, edition 

 1881 ; Pog-o-. Ann. vol. cxxiv. p. 476), where I have an old note 

 concerning this theory, and which I had forgotten, to the effect 

 that the radiation from platinised platinum was much greater 

 than that from smooth platinum, but that the increase was 

 chiefly in the ultra-red rays, for that the difference between the 

 two plates was almost completely annulled by a plate of alum. 

 This is what would be expected from the above theory, because 

 corrugations that are small enough to affect the ultra-red radia- 

 tions might still be too large to be anything but a smooth surface 

 for the visible radiations. There is evidently a good deal still 

 to be done on radiativity. Geo. Eras. Fitzgerald. 



Physical Laboratory, Trinity College, Dublin, 

 December 5. 



Flame. 



I TRUST that, in common with otherreaders of Nature, I feel 

 dulychastened by the homily which Dr. Armstrong has addressed 

 to you on the subject of my lecture on " Flame." It is perhaps 

 well that we should be warned from time to time against the 

 sin of dogmatising. The only objection I have to the process 

 is that I should be singled out as a sinner without some good 

 reason being given for the selection. I am charged with forget- 

 ting that certain alleged facts "are but phenomena interpreted 

 by our own limited intelligence," and yet I actually wound up 

 my lecture with a quotation from Carlyle, intended to emphasise 

 that very point. If Dr. Armstrong had said that this was an 

 "appeal to the gallery," I should not have complained. 



I do not feel equal to the metaphysical discussion to which 

 Dr. Armstrong opens the way. I know only of one kind of 

 fact, namely, " phenomena interpreted by our own limited in- 

 telligence," and it seems better to spell the thing in four letters 

 than to bury it in phrases that smack of the pulpit. 



Now let us see what I have done. I found on burning a 

 hydrocarbon with a limited supply of oxygen, that in the cooled 

 products of combustion all the carbon was oxidised, and that 

 some of the hydrogen was set free. I had been brought up, 

 like Dr. Armstrong, to cherish certain chemical dogmas, one 

 of which was that the hydrogen of a burning hydrocarbon was 

 oxidised before the carbon. I now asked myself what were the 

 grounds for this dogma ? It seemed to me to spring from the 

 narrowest view of things, probably from the fact — I mean the by- 

 limited-intelligence-interpreted-phenomenon — that hydrogen gas 

 is easier to set on fire than a lump of charcoal. This was obviously 

 an unscientific conclusion, for the carbon of a burning hydr - 

 carbon is part of a gas, and when it is oxidised it has not, like 

 a lump of charcoal, to be virtually gasified in the act of burning, 

 and so to demand a high temperature and an untold amount 

 of heat. I then read with great profit a paper by Dr. Armstrong, 

 which confirmed my opinion that the heat of combustion of an 

 atom of gaseous carbon, in forming carbon monoxide, must be 

 exceedingly high, and so on all grounds I concluded that there 

 was r\o fri?na facie reason for assuming that the hydrogen ot a 

 hydiocarbon would be oxidised in preference to the carbon. 

 Experiment showed the opposite result; the carbon was oxidised, 

 and I adopted the straightforward explanation, and renounced 

 the old dogma. There were alternative explanations. It was 

 conceivable that the hydrogen burnt first and liberated the car- 

 bon, which then acted upon the steam to produce one or both of 

 the oxides of carbon and free hydrogen. We should then have 

 two successive chemical reactions. I pointed out that there was 

 only one piece of indirect evidence in favour of this view, and 

 that has since been contradicted by Prof. Dixon. But Dr. 

 Armstrong appears to suggest the view that the two chemical 

 reactions are simultaneous. Now we know of plenty of chen - 

 ical reactions which are best understood and remembered if 

 we represent them by two simultaneous equations. When, for in- 

 stance, zinc is heated with strong sulphuric acid, and we do not 

 get hydrogen, we may explain the apparent anomaly by saying 

 that hydrogen is liberated, but that it immediately attacks some of 

 the hot sulphuric acid, producing sulphur dioxide and water. 

 Or we may choose another pair of " normal" reactions which, 

 being supposed to happen simultaneously, will explain the " ab- 

 normal " result. But surely no one thinks that the two re- 

 actions do proceed simultaneously. I use this method of expo- 

 sition very largely, but I always tell my students that it is 

 analogous to the treatment of forces in dynamics. We suppose 



