October 18, 1895.] 



SCIENCE. 



523 



myself, and must have used them in a moment 

 of mental aberration. I should have said that 

 the bolometer had given us most of the reliable 

 data concerning the absorption and transmis- 

 sion of radiant energy by the atmosphere, al- 

 though at that time I fully believed, both from 

 a general knowledge of Prof. Langley's work, 

 and from conversations with him, that the at- 

 mosphere was a pretty good valve. Prof. Davis's 

 references and a recent study of the published 

 data show that the valve is leaky indeed. Still, 

 if the atmosphere absorbs 50;^ of the Sun's 

 radiations, and 50 fo of those from the earth, 

 we have 25^ of the Sun's radiations let in and 

 not let out. If we take the figures which I be- 

 lieve Langley recommends, 70;?^ for the solar, 

 and 40 fo for the terrestrial radiations, we should 

 have a catch of 40 fo of that originally arriving 

 from the Sun. 



Many unexplained points concerning this 

 complex problem continually appear. What 

 becomes of the 30-40 fo of the solar radiations 

 and the 40 fo of terrestrial radiations absorbed 

 by the atmosphere ? It has but little mass and 

 low specific heat, and yet it does not get hot, 

 except in its lower layers. This source of en- 

 ergy it seems to me would be more than suf- 

 ficient for all meteorological phenomena. Prof. 

 Langley's data, voluminous and wonderful as 

 they are, still appear incomplete in certain very 

 important directions, leaving a very attractive 

 field for investigation. 



As to terminology, it seems to me very con- 

 venient to speak of ' heat rays ' so long as we 

 know exactly what we mean by the expression. 

 We are all familiar with 'light rays,' and a 'heat 

 ray ' is the same thing, only, as Maxwell says, 

 considered in its 'thermal aspect.' The term 

 ' ray ' is no doubt bad, but it is convenient and 

 should be permissible with a tacit understanding 

 that it is only a makeshift term. It would, of 

 course, be better if we had some term to signify 

 energy in its radiant form, as to direction of 

 propagation, wave front, etc., but so long as we 

 have not, and inasmuch as we all recognize 

 its identity, why not use the old names and 

 avoid multiplication of words. Even Prof. Lang- 

 ley's 'Luminous heat' ought to mislead no one; 

 evidently he refers to the heat effects of that 

 kind of radiant energy which is also capable of 



producing light effects ; ' dark heat rays ' are in- 

 capable of so doing. When Professor Langley 

 speaks of the ' radically different character of 

 the heat in two maxima' he refers, of course, to 

 their different wave-lengths. A similar remark 

 about a treble and bass note would not mislead 

 any one into the idea that both were not sound. 

 I fail to see what is wrong with the last quota- 

 tion from my article, or exactly what is meant 

 by the ' mis-recognition of the early part of this 

 century. ' 



I sympathize most sincerely with Professor 

 Davis in his demand for precise terminology, 

 but we must not allow even this worthy desire 

 to lead us into complexities of expression which 

 may be even more fatal to perspicuity than old 

 terms with modern significations. 



W. Hallock. 



CoLUJEBiA College, October 11, 1895. 



A REPLY. 



Editor of Science : If it be fair to presume, 

 as does Dr. Emory McClintock on page 453^ 

 of Science, under a heading which I think 

 should be 'Professor Halsted Corroborated,' 

 that because neither in a private letter nor in 

 print one specifies his many mistakes, therefore 

 one did not disapprove both his ' half on Sac- 

 cheri as well as the half on Gauss, ' then I must 

 beg of Science a line to say that among other 

 mistakes in this letter of his, he is completely 

 wrong in saying of me : ' ' He found that the 

 two words diuturnum prcelium were meant by 

 Saccheri to indicate a mental attitude of con- 

 stant war against the 'hypothesis' as heretical." 

 George Bruce Halsted. 



Austin, Texas, October 7, 1895. 



THE RUDOLF LEUCKART CELEBRATION. 



Several months ago the following circular 

 (Cf. Science, Vol. I., p. 187) was sent out from 

 Leipzig, s igned by about a hundred and fifty 

 scientists from various parts of the world : 



" Zur Feier des am 13 December, 1895, statt- 

 findenden funfzigjahrigen Doctorjubilaums von 

 Rudolf Leuckart, dem Nestor unter den deut- 

 schen Zoologen, dessen Wirken weit iiber den 

 Kreis seiner Specialwissenschaft hinausreicht, 

 fordern die ergebenst Unterzeiclmeten zu Bei- 

 tragen auf. Im Herzen seiner zahlreichen 



