lOO 



NATURE 



[November 30, 1893 



The plates illustrate most fully the points made out, 

 in many cases a longitudinal section of the skull of the 

 animal at birth being printed in red over a drawing of 

 one of adult age, both drawings having been reduced to 

 scales which render comparisons of form possible. 



LETTERS TO THE EDITOR. 



[T/te Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 inani'scripts intended for this or any other part «?/" Nature. 

 No notice is taken of anonymous co7mnunications .\ 



Suggested Nomenclature of Radiant Energy. 



Having recently had occasion to develop the first principles 

 of the theory of inter-stellar radiation, I soon felt the want of 

 some short and convenient word to express that form of ethereal 

 wave-effect known as "radiant energy," "radiant heat," 

 "light," "rays of the spectrum," &c. Radiant energy is 

 doubtless the most accurate of these expressions, but it is sutjject 

 to the objection of being a description rather than a name. The 

 nomenclature of the subject has come down from a time when it 

 was supposed that there were three distinct kinds of rays in the 

 spectrum, severally known as light, heat, and actinic rays. It 

 is, I believe, not much more than half a century since several 

 eminent physicists and teachers supposed that the heat rays of 

 the spectrum could be separated from the light rays having equal 

 refrangibility by the absorption of a transparent medium ; and 

 that even the light rays of different colours might be separated 

 in the same way. I cannot but think that the general under- 

 standing and application of the now received theory of the 

 subject, which recognises in this form of energy no differences 

 of kind except wave-length, has been materially retarded by the 

 want of a corresponding nomenclature. 



The use of the word "light" for ethereal waves having a 

 length between certain definite limits, while there is no corres- 

 ponding word for other waves, is evidently unscientific. Not- 

 withstanding the great practical usefulness of light, its distinnive 

 property of affecting the optic nerve in a certain way can claim 

 only a secondary place in physics. Indeed, it has long seemed 

 to me that the banishment of the word " light " from physics 

 was a desideratum. 



After various attempts I hit upon the very simple term 

 radiance, as one which seemed well-fitted to supply the want in 

 question. The vague and poetic idea hitherto associated with it 

 IS an advantage, because it enables us to adapt it to the case in 

 hand with greater readiness than we could adapt a word which 

 already had some well-defined meaning. Shakespeare speaks 

 of the " sacred radiance of the sun " ; while Milton describes the 

 Deity as "Girt with omnipotence, with radiance crowned." We 

 can thus adopt the word to express scientifically what we now 

 consider to be electro-magnetic waves, or ethereal waves, with- 

 out that clashing of ideas which might arise from making a new 

 application of an old word, and without the awkwardness of 

 coining a new one. 



The necessary derivatives and compounds of the word can be 

 formed with as much ease as we should expect in the case. The 

 verb "radiate " will mean to emit radiance. I do not think 

 any confusion will arise if we use the word " illuminate " to 

 signify the throwing of radiance upon a material body, although 

 in ordinary language it implies light. Possibly the extent to 

 which it is used in a tropical sense may facilitate the widening 

 of its literal meaning. Radiometry would mean the measure of 

 radiance, and an instrument for effecting such a measure would 

 naturally be called aradiometer. It is perhaps unfortunate that the 

 instrument in question should then assume the name of Crookes' 

 beautiful little instrument, but an apology may be found in the 

 fact that the latter has not been used for the purpose of exact 

 measurement. The use of the word "radiometry" offers no such 

 difficulty. 



I am still a little perplexed for a word which shall express 

 the quality hitherto called transparency, diathermancy, &c. 

 Apparently we have no alternative but to continue the use of 

 one of these objectionable words, or invent some such new word 

 as transradiant, or transradious. 



The proper measure of radiance, and the only measure which can 

 be regarded as of real i mportance in physics, should be the amount 

 of energy radiated in unit time. This measure is equivalent to 



NO. 1257, VOL. 49] 



that of heat generated in unit time in the absorption of radiance 

 by a perfectly black body. If we reflect that this, and this 

 alone, measures the actual loss of internal energy by a radiating 

 body of any kind, whether ball of iron in a laboratory, planet, 

 star, or nebula, the importance of some simple nomenclature of 

 measurement will be evident. I should be much pleased if 

 physicists would find by actual trial whether the use of the pro- 

 posed words comes as natural to them as it has to me. 



Simon Newcomb. 



The Postal Transmission of Natural History 

 Specimens. 



It has always been recognised that scientific research is 

 greatly furthered by the exchange of the various objects with 

 which that research is concerned. For the transmission of 

 objects of Natural History from one country to another, the 

 mails have offered a cheap, speedy, and trustworthy means. 

 Heretofore, through the laxity with which the regulations on 

 the subject have been enforced, it has been possible to enter 

 such objects in the mails of the Universal Postal Union as 

 samples of merchandise and under the rates of postage there- 

 for. From ofhcial information lately received from the Post 

 Office Department of the United States it appears that such a 

 rating is entirely unauthorised by existing provisions, and that 

 objects of Natural History may be mailed to countries of the 

 Union only, at the rates required for letters. The United States 

 Post Offics Department also stated that it had recently sub- 

 miued a proposition to the countries composing the Postal 

 Ui.ion to modify the regulations so that such specimens might 

 be received into the mails at the same rates as samples of 

 m 5rchandise, but that a sufficient number of those countries had 

 voted against the proposition to defeat it. 



This Academy has therefore resolved to address the various 

 scientific bodies, with which it is in communication, in those 

 countries whose Governments have voted against the proposi- 

 tion, and to request those scientific bodies to memorialise their 

 respective Governments in favour of the same. 



The Governments of Austria, Bolivia, British India, Canada, 

 Germany, Great Britain, Guatemala, Hungary, Japan, Norway, 

 Portugal, Russia, Spain, Sweden, Tunis, Uruguay, and 

 Venezuela having voted in the negative, this Academy respect- 

 fully requests the favourable conhideration of this question by 

 scientific societies, and begs that they take such steps as they 

 deem advisable to inform the Postal authorities of their 

 respective Governments of the manifest advantages to scientific 

 research which would result from the adoption of the proposed 

 modification, and to request those authorities to take such steps 

 as may result in the adoption of the same. 



The letter rate for postage (Universal Postal Union) is ten 

 times that required for samples of merchandise ; such a rate 

 for specimens of Natural History is virtually prohibitive. 



This Academy would respectfully urge upon scientific 

 societies prompt action in this matter, if it meets with that 

 approval which we so strongly desire. 



Isaac J. Wistar, President. 



Edvv. j. Nolan, Recording Secretary. 



Philadelphia, November 14. 



Flame. 1 



However thoroughly a B.A. audience may have allowed 

 Prof Smithells, by means of his beautiful experimental demon- 

 strations, to hypnotise them into unquestioning belief in his 

 conclusions, those who read the account of his lecture in 

 the pages of Nature will not all be equally disinclined to 

 question the validity of some of his arguments. 



To tell us that Dalton, as a matter of fact, long ago settled 

 the question as to which has the preference — the carbon or the 

 hydrogen — when a hydrocarbon is burnt with insuflicient 

 oxygen, is, after all, but to appeal to the gallery ; and this and 

 other conclusions arrived at by Prof. Smithells appear to me to 

 involve the use of that process of circular reasoning which con- 

 sists in taking for granted that which is to be proved — a method 

 which at the present day finds such favour in certain quarters. 



As I discussed this matter somewhat in detail in a correspon- 

 dence with Sir G. G. Stokes last year (Chem. Soc. Proceedings, 

 1892, No. 106, p. 22), it is unnecessary to go fully into it now. 

 Any number of analyses showing the presence of hydrogen in 

 the products of combustion may be quoted without materially ad- 



