246 



NATURE 



[July io, 1890 



the accuracy of Mr. Stanley's report, nor the trustworthiness of 

 Emin's observation ; but we should like to have more details." 

 But as Emin himself allows that he would never have credited the 

 fact alleged had he not witnessed it personally, we may, per- 

 haps, without discourtesy, refuse to accept so bald a statement 

 of "this extraordinary spectacle." Of what were the torches 

 constructed? How do these "Simians" practise "the art of 

 making fire " ? Having once acquired the art, do they use it 

 only for the purpose of making " torches to light the way " ? 



Speaking for myself, and not without some knowledge of the 

 intelligence of a chimpanzee, I confess that, until at least these 

 "details" are supplied, I do "doubt the trustworthiness of 

 Emin's observation," and I shall be satisfied to suppose that, 

 owing to a shortsightedness of which we have heard so much, 

 the Pasha has mistaken a band of native children for bis "large 

 tribe of chimpanzees." George J. Romanes. 



July 6. 



Dr. Koenig's Theory of Beats. 



I MADE an experiment, some years ago, which would seem to 

 support and illustrate Dr. Koenig's theory of beats, as set forth 

 by Prof. Silvanus Thompson in his lecture before the Physical 

 Society, and reported in your issue of June 19. Taking two 

 tuning-forks, each of which gave the middle C (256 vibrations;, 

 I weighted one of them so as to make it give one beat a second 

 when sounded with the other. Then, sounding this fork, so 

 weighted, with another giving the fifth above, G (384 vibra- 

 tions), I heard distinctly three beats a second. I could only 

 account for these beats by assuming that the weighted fork C 

 produced a feeble twelfth, and that the fork G produced a feeble 

 octave. These two overtones would, if present, give three beats 

 a second, 255 x 3 = 765, and 384 x 2 = 768. But I could not 

 show by any independent evidence that these overtones are 

 really present when the tuning-forks are sounded ; and, in fact, 

 the general opinion is against such an assumption. 



If, however, Dr. Koenig's theory be accepted, the beats are 

 easily accounted for. According to his view, as stated by Prof. 

 Thompson, these forks when sounded together would yield two 

 sets of beats, called, respectively, superior and inferior ; and 

 each set of beats would blend into a musical tone. Thus we 

 should get — 



Inferior beat 384 - 255 = 129 



Superior beat 510 - 384 = 126 



These primary beats, or beat-tones as they may be called, of 

 129 and 126 vibrations would act as independent tones, and 

 produce secondary beats of three in the second. 



I hope Prof. Thompson's paper will be published in full, that 

 we may all have an opportunity of considering the details of 

 Dr. Koenig's reasoning ; but, in the meantime, I thought the 

 experiment I have described would be interesting to your readers, 

 as it is very easily made. Perhaps I should add that the ex- 

 periment succeeds equally whether the forks are mounted on 

 resonance-boxes or not ; and therefore the effect cannot be 

 ascribed to the boxes. Gerald Moli.oy. 



Catholic University, Dublin, June 22. 



The "Night-shining Clouds." 

 I HAVE not yet seen, in any English publication, mention of 

 the important results of the more recent researches of Herr O. 

 Jesse and his coadjutors on these clouds. By taking simulta- 

 neous photographs from two or more widely separated places, 

 the height of the clouds has been determined with great exact- 

 ness. On July 2, 1889, this was found to be somewhat over 

 80 kilometres. The operations have evidently been conducted 

 with great care, and the results may therefore be fully trusted. 

 The question is therefore set at rest as to whether the clouds 

 are self-luminous, for it is evident that at such a height their 

 brightness is fully accounted for by the sun shining upon 

 them. In 1886, Herr Jesse had, upon this supposition, ascer- 

 tained their brightness to be from 49 to 54 kilometres, and 

 that the lower the sun descended the smaller wa^ the illumina- 

 tion needed to show them as the atmosphere darkened, so that 

 the calculated height increased with the sun's depression below 

 the horizon. Some people were incredulous about the great 

 height at that time attributed ; but the photographs give them 

 a yet greater elevation, which places them quite out of the 

 category of any ordinary clouds. Those who Iwve not seen the 

 photographs may query as to the possibility of identifying the 



NO. 1080 VOL. 42] 



same points in the two photographs compared, and may think 

 that even synchronous photographs might show very different 

 details by being taken from two distant stations ; but, on the 

 contrary, in those examples I have seen, the two photographs 

 are so exactly alike that it is very difficult to discover any differ- 

 ence whatever between them, though taken at Nauen and Steg- 

 litz, 35 kilometres apart, which consideration of itself shows the 

 enormous height of the clouds. In some of the photographs the 

 stars o and /3 Aurigse are distinctly visible. 



The letter by "M. E." (p. 198) evidently describes an 

 apparition of these clouds on the night of the 17th ult., when, 

 as I am informed, they were also seen from Sunderland ; but I 

 have not myself seen them either this year or last, though they 

 have been seen both years in Germany — more especially after 

 midnight. They generally are seen in June and July, the 

 earliest recorded date being May 26, and the latest August 1 1. 



Sunderland, July 8. T. W. Backhouse. 



In a letter which you published some time ago on "night- 

 shining clouds," there was a request for notes of their occurrence. 

 It may, therefore, interest some of your readers to know that they 

 were well seen here on the evening of the 4th inst. They ap- 

 peared rather suddenly shortly before 10 p.m., covering the sky 

 from N. to N.E., and from the horizon for about 15° up. They 

 vvere not in regular strata, but scattered in all directions, like 

 cirrus after a storm. About midnight they were still visible, but 

 more to the left, some being west of north. The first time I 

 saw these clouds was on June 18, 1886, soon after midnight, 

 vvhen they were about N.W,, and 20° from the horizon, and 

 since then they have often been seen ; but never, so far as I 

 know, with the storm-tossed appearance they presented last 

 week. Cecil Shaw. 



Belfast, July 7. 



A very fine display of luminous nig;ht-clouds waj visible here 

 during the night of the 4th inst., the luminosity extending to an 

 altitude of 30° above the northern horizon, ending above in 

 definite cirrous streamers, or cloud wisps. It will be seen by 

 the Ben Nevis June Summary that these clouds were noted on the 

 29th ult. In Nature of the 3rd inst. (p. 222), the writer's com- 

 munication on this subject was misprinted Kensington instead of 

 Kingstown (Co. Dublin). The present dates from Scotland. 



Aberdeen, July 7. D. J. Rowan. 



An Electrical Effect. 



It may be of value to remind teachers of an effect not gener- 

 ally known, which is produced by varying the ordinary mode of 

 performing the experiment of putting pieces of zinc and silver 

 in the mouth and touching them, to obtain the acid taste which 

 accompanies the completion of the electric circuit. 



If the piece of zinc be placed under the tongue, and a florin 

 vertically between the upper lip and the top row of teeth, and 

 the two metals be brought in contact, a faint flash is seen in 

 both eyes when the eyes are open. 



If the eyes are shut the sensation of light is not felt, so that 

 the effect is probably due to a muscular twitching. 



It is necessary to use a large silver coin, and not a shilling, 

 and to push it well home behind the upper lip. 



The experiment so made seems to be a handyo and simple 

 illustration of the meaning of subjective phenomena. 



Clifton College, July 7. Edward B. Cook. 



THE PHOTOGRAPHIC IMAGE} 

 'IP HE history of a discovery which has been developed 

 -*■ to such a remarkable degree of perfection as photo- 

 graphy has naturally been a fruitful source of discussion 

 among those who interest themselves in tracing the pro- 

 gress of science. It is only my presence in this lecture 

 theatre, in which the first public discourse on photography 

 was given by Thomas Wedgwood at the beginning of the 

 century, that justifies my treading once again a path which 

 has already been so thoroughly well beaten. If any further 

 justification for trespassing upon the ground of the his- 

 torian is needed, it will be found in the circumstance that 

 in the autumn of last year there was held a celebration 



' Friday Evening Lecture delivered at the Royal Institution by Prof. 

 Raphael Meldola, F.R.S., on May 16, 1890. 



