94 



NA TURE 



[Nov. 27, 1884 



million vibrations per second ; then the lowest radiant heat, as 

 yet investigated, is about 100 million million per second in the 

 way of frequency of vibration. 



I had hoped to be able to give you a lower figure. Prof. 

 Langley has made splendid experiments on the top of Mount 

 Whitney, at the height of 15, coo feet above the sea-level, with 

 his "bolometer," and has made actual measurements of the 

 wave lengths of radiant heat down to exceedingly low figures. 

 I will read you one of the figures ; I have not got it by heart 

 yet, because I am expecting more from him. 1 I learned a year 

 and a half ago that the lowest radiant heat observed by 

 the diffraction method of Prof. Langley corresponded to 

 2S/loo,oooths of a centimetre for wave length, twenty- 

 eight as compared with red light, which is 7-3 ; or nearly 

 fourfold. Thus wave lengths of four times the amplitude, or 

 one-fourth the frequency per second of red light have been 

 experimented on by Prof. Langley, and recognised as radiant 

 heat. 



Photographic, or actinic light, as far as our knowledge 

 extends at present, takes us to a little less than one-half the 

 wave length of violet light. You will thus see that while our 

 acquaintance with wave motion below the red extends down to 

 one-quarter of the slowest rate which affects the eye, our know- 

 ledge of vibrations at the other end of the scale only comprehends 

 those having twice the frequency of violet light. In round num- 

 bers we have four octaves of light, corresponding to four octaves 

 of sound in music. In music the octave has a range to a note of 

 double frequency. In light we have one octave of visible light, 

 one octave above the visible range, and two octaves below the 

 visible range. We have 100 per second, 2C0 per second, 400 

 per second (million million understood) for invisible radiant heat, 

 800 per second for visible light, and 1600 per second for 

 invisible light. 



One thing in common to the whole is the heat effect. It is 

 extremely small in moonlight, so small that nobody until re- 

 cently knew there was any heat in the moon's rays. Herschel 

 thought it was perceptible in our atmosphere by noticing that it 

 dissolved away very light clouds, an effect which seemed to show 

 in full moonlight more than when we have less than full moon. 

 Herschel, however, pointed this out as doubtful ; but now, 

 instead of its being a doubtful question, we have Prof. Langley 

 giving as a fact that the light from the moon drives the indicator 

 of his sensitive instrument clear across the scale, and with a 

 comparatively prodigious heating effect ! 



I must tell you that if any of you want to experiment with the 

 heat of moonlight you must compare the heat with whatever 

 comes within the influence of the moon's rays only. This is a 

 very necessary precaution ; if, for instance, you should take your 

 bolometer or other heat detector from a comparatively warm 

 room into the night air. you would obtain an indication of a fall 

 in temperature owing to this change. You must be sure that 

 your apparatus is in thermal equilibrium with the surrounding 

 air, then take your burning-glass, and first point it to the moon, 

 and then to space in the sky beside the moon ; you thus get a 

 differential measurement, in which you compare the radiation of 

 the moon with the radiation of the sky. You will then see that 

 the moon has a distirctly heating effect. 

 ( To be continued. ) 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 

 Cambridge. — The Professorship of Political Economy will be 

 filler! up on Dec. 13. The Higher Local Examinations were held 

 last June at 21 centres, and attended by 960 candidates (chiefly 

 women), a decrease of 27. In Arithmetic the work of most of 

 the candidates was by no means good. Euclid's propositions 

 were well and neatly written out. In some cases attempts were 

 made to improve upon Euclid, but usually with disastrous results. 

 Thebcok-work of Geometrical Conies was fairly done by the few 

 who attempted it, but only one rider out of four was solved by 

 any candidate. Only a few candidates tried Analytical Geo- 

 metry, and they nearly all did badly. Some very intelligent 

 work was sent up in Algebra and Trigonometry. In Statics and 



1 Since my lecture I have heard from Prof. Langley that he has 

 the refrangil .ilt prism, and inferred the wave length of heat 



rays from a "Leslie cube" (a metal vessel of hot water radiating from a 

 blackened side). The greatest wave length he has thus found is one- 

 thousandth of a centimetre, which is seventeen times that of sodium light. 

 The corresponding period is about thirty million million to the second. 



Dynamics the majority of candidates had made but little way. 

 The attempts at Astronomy were few and generally slight. 

 Altogether, in Group C (Mathematics), there were only 140 

 candidates, of whom 41 failed, 70 obtained a third class, and 

 only 12 attained a first class. 



In Political Economy many of the answers were vague and inde- 

 finite. In Logic the simpler questions were well answered, and 

 Mill's inductive methods were understood. Of 45 candidates, 

 however, only 2 gained a first class. 



In Group E (Natural Science), out of 62 candidates 25 failed, 

 while 5 obtained a first class. In Elementary Chemistry and 

 Physics the answers were mostly unsatisfactory ; Elementary 

 Biology was much better done. Very few candidates seemed 

 to connect the definitions of Chemistry with the facts. 



In Physiology and Zoology marked improvement was shown 

 in the answers. The principal fault was still the want of per- 

 sonal acquaintance with phenomena that might be easily ob- 

 served. In Botany the descriptions of plants were fairly well 

 done, and the questions on Vegetable Physiology were attempted 

 with some success by several candidates. No candidate, how- 

 ever, gave a good description of the germination of a seed. 



In Physical Geography and Geology the answers were, on the 

 whole, very good, and remarkably free from errors. The one 

 common failing was the absence of good diagrams. 



Mr. James Sully, M.A. Lond., has been appointed a member 

 of the Board of Electors to the Professorship of Mental Philo- 

 sophy and Logic, in place of the late Dr. Todhunter. 



Dr. Donald Mac A lister has been appointed by the Senate to 

 be an Examiner in Medicine. 



M S.NCHESTER. — At a meeting of the Council of the Victoria 

 University, Owens College, on Friday, November 21, Mr. J. H. 

 Fowler, B.A. (Oxon.) was elected, on the recommendation of 

 the Senate, to a Berkeley Research Fellowship in Zoology. The 

 Piatt Physiological Scholarship, which is also for the encourage- 

 ment of original research, has been awarded to Mr. C. F. 

 Marshall, B.Sc. (Viet.). 



SCIENTIFIC SERIALS 



Journal of the Anthropological Institute of Great Britain an i 

 Ireland, November 18S4. — The ethnology of Egyptian Soudan, 

 a timely and important paper, by Prof. A. H. Keane. — Addi- 

 tional observations on the osteology of the natives of the An- 

 daman Islands, by Prof. Flower. — The Kubus, a small tribe in 

 Central Sumatra, by Mr. Forbes. — Notes on prehistoric re- 

 mains in Antiparos, by Mr. Theodoie Bent. — The Deme and 

 the Horde, by Messrs. Howitt and Fison ; an attempt to show 

 a resemblance between the general organisation and usages of 

 the Attic tribes and those of the Australian aborigines. — African 

 symbolic messages, by the Rev. C. Gollmer, describing the 

 method in which natives of the Yoruba country send messages 

 to absent friends by means of shells, feathers, corn, stone, 

 coal, sticks, &c, — On the size of teeth as a character of race, 

 by Prof. Flower. — A Hindu prophetess, by Mr. Walhouse. — 

 On certain less familiar forms of Palaeolithic flint implements 

 from the gravel at Reading, by Mr. Shrubsole. 



The American Journal of Science for November contains : — 

 Mr. Asa Gray's paper on the characteristics of the North Ameri- 

 can flora, read before the Biological Section of the British Asso- 

 ciation at the Montreal meeting ; also columbite in the Black 

 Hills of Dakota, by Mr. Blake : spectro-photometric study of pig- 

 ments, by Mr. Nichols ; criticism of Becker's theory of faulting, 

 by Mr. Ross Bourne ; the difference between sea and continental 

 climate with regard to vegetation, by Mr. Buysman ; chemical 

 affinity, by Mr. J. \V. Langley ; the relation between the electro- 

 motive force of a Daniell cell and the strength of the zinc 

 sulphate solution, by Mr. Carhart ; a notice of the remarkable 

 marine fauna occupying the outer banks of the southern coast of 

 New England, by Sir. Verrill ; and a note by Mr. J. D. Dana, 

 on the Costlandt and Struy Point hornblendic and augitic rocks. 



Rivista Scicnti/ico-Iuilustriale, October 30. — On the origin of 

 atmospheric electricity, of thunder-storms and volcanic erup- 

 tions (continued), by Prof. Giovanni Luvini. — Note on a simple 

 method for determining the velocity of a railway train, by Prof. 

 Steiner. — Note on Bauer's new radiometer, by the Editor. — On 

 the vitality of insects in oxygen, hydrogen, carbonic acid, and 

 prussic acid, by the Editor. 



