512 



NATURE 



[April 2i^, 1872 



and with considerable brightness, chiefly from half-past eight to 

 ten o'clock. 



During the phenomenon several falling stars were observed, 

 and a magnificent bolide in the Great Bear at 8h. 30m., but this 

 was probably accidental. 



This evening, in the expectation that the aurora borea'is miglit 

 reappear, I began to observe the sky as soon as twilight was 

 over, and I perceived a faint glow, a kind of phosphorescence, dif- 

 fused over the whole sky, but without any decided appearance of 

 boreal light. 



While waiting for more imposing phenomena, I directed the 

 spectroscope towards the zodiacal light, to ascertain whether its 

 spectrum could be observed at Rome, as it had been observed on 

 the Red .Sea on the evening of the nth, and the morning of the 

 1 2th January last. 



Angstrom, in 1867, found the spectrum of the zodiacal light lo 

 be monochromatic, consisting of a single green line, to which 

 he assigned approximately the position 1259 on Kirchhoff's scale, 

 the same that he had determined for the green line of the aurora 

 borealis ; and I myself, on the days above mentioned, was able 

 to perceive in the zodiacal light, not only this green line, but near 

 it and towards the blue, a band or zone of apparently continuous 

 spectrum. 



This evening at seven o'clock, I was able to discern the same 

 spectrum in the light above mentioned ; and on directing the 

 spectroscope to other points, I found that this spectrum showed 

 itself in all parts of the heavens from the horizon to the zenith, 

 more or less defined in different parts, but everywhere as bright 

 as in the zodiacal light. The observatory assistant, Dr. di 

 Legge, likewise observed this spectrum distinctly, in various 

 parts of the heavens. 



This fact, which corroborates an analogous observation made 

 by Angstrom in 1867, appears tome of the greatest importance, 

 inasmuch as it demonstrates the identity of the zodiacal light 

 with that of the aurora, and thereby tends to establish the iden- 

 tity of thtir origin, and to unite into one these two mysterious 

 phenomena. L. Respighi 



Observatory of the Roval University of CampidogU), 

 Feb. 5, 1S72. 



PHYSrOLOGV 

 Note on Recurrent Vision* 



In the course of some experiments with a new double plate 

 Holtz machine, belonging to the college, I have come upon a 

 very curious phenomenon, which I do not remember ever to 

 have seen noticed. The machine gives easily intense Leyden 

 jar sparks from seven to nine inches in length, and of most daz- 

 zling brilliance. When, in a darkened room, the eye is screened 

 from the direct light of the spark, the illumination produced is 

 sufficient to render everything in the apartment periecily visrble ; 

 and what is renrarkabie, every cons^ icuous objccc is seen hviie 

 at least, with an interval of a trifle less than one quarier of a 

 second — the first time vividly, the second time faintly ; often it 

 is seen a third, and sometimes, but only with great difficulty, 

 even a fourth time. The appearance is precisely as if the object 

 had been suddenly illuminated by a light at first bright, but 

 rapidly fading to extinction, and as if, while the illumination 

 lasted, the observer were winking as fa-.t as possible. 



I see it best by setting up in front of the mach ne, at a dis- 

 tance of eight or ten feet, a white screen having upon it a bUck 

 cross, with ar'trs about three fe^t long and one fuot wide, made 

 of strips of cambric. That ihe phirirunienoii is realiy subjective, 

 anl not due to a succession of spa ks, is easr y shawn by swing- 

 ing the screen from side (o side. Tnc blick cross, at all the 

 periods of visibility, occupies lire sam.- plac-, and is apparently 

 stationarv. The same is true of a sciobosciop.c disc m rapid 

 revo ution ; it is seen several ames by each spark, but each lime 

 in the same po ition. There is no apparent multiplication ol a 

 moving object of any sort. 



The interval between the successive instants of visibility was 

 measured roughly as follows : — A tuning fork, making 92.^ 

 vibrations per second, was adjusted, so as to record its motioir 

 upon the smoked surface of a revolving cylinder, and an el ctro- 

 magnet was so arranged as to record anv motion of its armaiure 

 upon the trace of the fork : a key connected with this magnet 

 was in the hands of the observer. An assistant turned the 



♦ From the Amcruait Joiininl cf Siiince and Art ior h-gxW. By Prof. 

 C, A. Young, of Dartmouth CoUegq, _ 



machine slowly, so as to produce a spark once in two or three 

 seconds, while the observer manipulated the key. 



In my own case the mean of a dozen experiments gave o''22 

 as the interval between the first and second seeing of the cross 

 upon the screen; separate results varying from o^'I7 to 0^'30, 

 Another observer found o"24 as a result of a similar series. 



Whatever the true explanation may turn out to be, the phe- 

 nomenon at least suggests the idea ot a reflcclion of the ua-'oiis 

 impulse at the nerve extremities — as if the intense impression 

 upon the retina, after being the first time propagated to the 

 brain, were there reflected, returned to the retina, and from the 

 retina travelling again to the brain renewed the sensation. I 

 have ventured to call the phenomenon "Recurrent vision." 



It may be seen, with some difficulty, by the help of an induc- 

 tion coil and Leyden jar ; or even by simply charging a Leyden 

 j ir with an old-fashioned electrical machine, and discharging it 

 in a darkened room. The spark must be, at least, an mch in 

 length. 



Hanover, February 9 



SCIENTIFIC SERIALS 



Annales de Chimie et de Physique, July and August, 1S71. 

 This number contains the second portion of a very lengthy 

 memoir by M. Berthelot on explosive agents in general ; this 

 half of the communication deals with dynamite, gun cotton, 

 picric acid and potassic picrate. At the end of the memoir a 

 general table is given which shows the amount of heat generated 

 and the volume of gas formed by one kilogram of substance ; 

 the product of these two numbers will of course give the relative 

 effects produced by each compound ; the numbers given show 

 that if nitroglycerine produces an amount of force equal to 94, 

 picric acid equals 54, gun cotton 50, potassic picrate 34, whilst 

 gunpowder has only an explosive force equal to 14. M. Jansseu 

 contributes a very valuable paper on the atmospheric lines in the 

 solar spectrum. He finds that the bands observed by Brewster 

 and Gladstone can be resolved into fine lines comparable to the 

 solar lines properly so called, and that the atmospheric lines are 

 more numerous than the solar lines in the red, orange, and 

 yellow portions of the spectrum. The atmospheric lines are 

 always visible in the solar spectrum, some lines it is true almost 

 disappear when the sun is very high, but they are those which 

 are never very intense ; the author finds that the intensity of the 

 atmospheric lines observed at the horizon is about fifteen times 

 as great as when observed in the meridian. M. Janssen has also 

 examined the spectrum of the moon and stars, and more particu- 

 larly of Sirius and a in Orion ; he has not succeeded in observing 

 any new lines whatever in the spectrum of the moon, proving 

 that our satellite cannot have any appreciable atmosphere. 

 M. Raoult has found that a solution of cane sugar sealed up in 

 vacuo and exposed to light for five months is partially changed 

 into glucose. Amongst the other original meipoirs there is a 

 very long one by Dr. de Coppet on the temperature of congela- 

 tion in saline solutions. There are also a considerable number of 

 abstracts of papers from foreign journals, making up altogether 

 a very bulky number. 



Ta^ Journal of the Quekett Microscopical Club, No. 18, April 

 1S72, Contains the following three communications : — " Observa- 

 tions on the Polyzoa, by A. H. H. Lattey, M.R.C. P." This 

 paper is chiefly devoted to the preparation of the Polyzoa for the 

 microscope, so as to exh'.bit them in permanence with the ten- 

 tacles expanded. — "On the so-called 'nerve' of the Tooth," by 

 T. C. White, Hon. Sec. The p incipal elements met with in a 

 microscopical examination of what is popularly termed the 

 "nerve "of the tooth, are here indicated, and suggestions are 

 given to assist in the more complete examination of tooth- 

 siructure. — " On the Internal Structure of the Pulex irritaus," by 

 W. H. Furlonge. This is a second communication on the 

 struc ure of the Ilea which has been submitted to the club by its 

 author. The first was occupied chiefly in the examination of 

 external organs, the present is devoted to internal structui"e, 

 commencing with the alimentary and digestive system, then 

 f how remarks on the respiratory system, and finally observa- 

 tions on the reproductive system. The embryology is left 

 untouched, to form the subject of a third and concluding 

 paper, which will then embrace the life history of one of 

 the commonest, but not the least interesting, of British insects. 

 The club announced its _list of excursions for the geasoji conur 



