Jan. 15, 1SS0] 



NATURE 



267 



To study the fluorescent spectrum many physici.-ts adopt the 

 method of projecting a spectrum sufncitntly ) ure to show the 

 principal Fraunhofer lines, on a fluorescent body, solid perhaps, 

 or the side of a glass vessel containing a fluorescent liquid, and 

 determining the parts where the fluorescence appears, reaches a 

 maximum, and disappears. Others develop the direct spectrum 

 on the surface of a liquid ; Herr Hagenbach places the slit and 

 the prism horizontally, and projects the spectrum on the free sur- 

 face of the liquid. The disadvantages of these two methods M. 

 Lamansky [Jcur. dt Phys., Dec.) has sought to avoid in a spec- 

 troscope he has had recently constructed by M. Duboscq, and 

 which he finds very convenient. The collimator and the tele- 

 scope of this direct vision spectroscope are fixed separately on a 

 graduated circle ; they may be placed at various angles in the 

 vertical plane. The collimator is furnished with a small adjust- 

 able mirror for directing the luminous rays along the optic axis. 

 In the prolongation of the collimator tube is placed the direct- 

 vi.-ion prism and a lens which throws the spectrum on the surface 

 of the liquid contained in a small vessel on a table which can be 

 raised or lowered. The telescope is directed to the same liquid 

 surface, and the focal distance of the ordinary telescope is 

 .shortened by the addition of a second object-glass, which may be 

 removed at will. The division of ihe circle allows of deter- 

 mining the angles at which the coloured rays fall on the liquid 

 surface and the angles at which the fluorescent spectrum is ob- 

 served. A dark cloth may be thrown over the apparatus to 

 exclude disturbing light. 



An interesting observation on the supernumerary or spurious 

 rainbows occasionally seen lining the inner edge of the primary 

 arc of a rainbow has been made by M. Montigny. These 

 supernumerary rainbows usually consist of a red band touching 

 the violet on the inner side of the bow, followed by green and 

 violet, 'and passing again to red. Indeed it is possible occa- 

 sionally to observe as many as four or five recurrences of the red 

 and green tints. They are, however, almost always confined to 

 the highest portion of the bow, and are rarely observed near the 

 ground. M. Montigny, on August 30, 1S79, watching a rain- 

 bow near Rochefort, a little before sunset, noticed that while the 

 upper portion of the primary bow showed no trace of super- 

 numerary bows, the lower portions on each side, which came 

 out brilliantly against a stratum or zone of misty air, were fur- 

 nished with no fewer than four supernumeraries of paler tint. 

 According to the received theory of Young and Airy these bows 

 are due to diffraction, caused by very small drops, the smallest 

 drops giving the broadest and most brilliant fringes of colour. 

 Usually it happens that in the higher regions of the air the falling 

 drops are smaller than they are at the lower regions ; hence the 

 occurrence of supernumerary arcs at the upper part of the bow. 

 In M. Montigny's observation, doubtless, the misty zone lying 

 near the ground provided the drops of the requisite degree of 

 smallness to produce the diflfractive effects. This is, at least, 

 of the case. 



In the December number of Sdliman's Journal is a memoir of 

 extreme interest by Dr. E. L. Nichols on the character and 

 intensity of the rays emitted by glowing platinum. Several 

 tables of statistics of observations are given, and two graphic 

 charts which embody the tabular results. Reviewing the A priori 

 law of Kirchhoff, concerning the emission of rays of greater 

 refrangibility at higher and higher temperatures, he remarks : 

 "Strictly speaking, however, the temperature at which each 

 individual wave length becomes visible depends solely upon the 

 sensitiveness of the observer's eye. We are furthermore forced to 

 conclude from experiment that the more refrangible rays really 

 exist at temperatures far below those at which we begin to see 

 them. The directions of the curves (Plates I. and II.) seem to 

 denote that all the rays studied begin to be emitted at some 

 temperature not included in the interval embraced by the experi- 

 ments. / suspect indad that all of them originate at some very 

 low degree (the absolute zero ?), and are recognizable no sooner, 

 s:mply because the various instrt4metits at command, the thermopile, 

 eye, photographic plate, Sr'c., are not more delicate. That the 

 various colours do not appear simultaneously, follows from the 

 very different degrees of sensitiveness shown by the eye for 

 different rays." 



An interesting electric toy, contrived by M. Pfeiffer, is de- 

 scribed in a recent number of La Nature. It is a small electro- 

 phorus consisting merely of a thin plate of ebonite about I mm. 

 in thickness ; the usual wooden disk with tinfoil is replaced by a 

 small piece of tin about the size of a playing-card, attached to one 

 of the faces of the ebonite plate. This electrophorus produces 



electricity with great facility. You have merely to place it on a 

 wooden table and rub it successively on its two faces with the 

 open hand ; then on lifting it with the left hand and bringing the 

 right hand near the tin plate, a spark is obtained I to 2 centi- 

 metres long. Several small accessories, skilfully contrived, are 

 added to the electrophorus ; among these are dancing puppets 

 made of pith, which manifest very amusingly the phenomena of 

 electric attraction or repulsion. Electrify the ebonite plate, put 

 the three puppets on the tin, and then rai-e the plate from its 

 support. One small personage lifts his arms above his head ; 

 the hair of a second stands out ; and the third, lighter than the 

 others, jumps about like a clown, while two pith balls placed at 

 his side dance with him. M. Pfeiffer has also collected in one 

 small box all the known accessories of an electric machine ; a 

 miniature Leyden jar, an electric carillon, a Volta pistol, a 

 Geissler tube, &c. , these being operated with the electrophorus. 



SCIENTIFIC SERIALS 

 American Journal of Science and Arts, December, 1879. 

 — Mr. Brooks here calls attention to an important difference in 

 the breeding habits of American and European oysters ; the 

 eggs of the former are fertilised outside the body of the parent ; 

 and during the period which the European oyster passes inside 

 the mantle cavity of the parent, the young American oyster 

 swims at large in the open ocean. Mr. Brooks traces the 

 successive stages of oyster development. — Mr. Harting writes on 

 triple objectives with complete colour-correction. — There are 

 geological papers on Yirginia, on Galisteo Creek, New Mexico, 

 and on Catrosa Co., Georgia. — Prof. Yerrill describes two new 

 species of cephalopods caught off the coast of Massachusetts ; 

 also what is the second known representative of the remark- 

 able family of Cirroteulhida : — Dr. Nichol's researches on the 

 character and intensity of the rays emitted by glowing platinum 

 (see Nature, voL xxi. p. 1S4) are here given in detail. — Prof. 

 Marsh's notes on Jurassic dinosaurs, and Dr. Draper's researches 

 in photography of stellar spectra have been already noticed in 

 our columns. — Prof. Peters contributes observations on the 

 planets Hersilia and Dido ; and in the " Scientific Intelligence " 

 we note two useful lists of the (209) minor planets, numerical 

 and alphabetical. 



SOCIETIES AND ACADEMIES 

 London 



Royal Society, January S. — "On the Photographic Method 

 of Mapping the Least Refrangible End of the Solar Spectrum 

 (with a map of the Solar Spectrum from 7600 to 10750)," by 

 Capt W. de \V. Abney, F.R.S., R.E. 



The author refers to the sensitiveness of different forms ot 

 silver salts when exposed to the action of the spectrum, and 

 shows how he has been able to prepare, by methods indicated, 

 silver bromide which absorbs the red and ultra-red rays, and 

 which is sensitive to these rays. 



In his paper he describes the apparatus employed by him in 

 the photography of the invisible least refrangible rays, both with 

 a prismatic, and also with the diffraction apparatus. From 

 photographs taken with the latter, he has constructed a map 

 extending from A 7600 to A 10750, which he submits to the 

 Society. ° He shows also that in the photographs of the pris- 

 matic spectrum, he has apparently reached the limiting length 

 by comparing it with photographs of the diffraction spectrum. 

 The author has also compared Lamansky's prismatic thermo- 

 graph with his photograph. The paper closes with some 

 theoretical remarks on the silver compounds employed. 



Mathematical Society, January 8. — C. W. Merrifield, 

 F.R.S., president, in the chair. — Prof. W. S. Burnside was 

 elected a Member. — Prof. Cayley, F.R.S., communicated two 

 formula: in spherical trigonometry which are included in the one 

 form — 



, tan£<r(cos.S - isaiB) = tan(- - <p\ 



i = \' - 1 and tan (p = tan J b (cos A + i sin A). 

 The note which the President read at the last meeting simply 

 gives (as has been pointed out to him since) some symmetrical 

 cases of the orthogonal transformation, of a much more general 

 character (but unsymmetrical) given by Mr. Cayley, and repro- 

 duced in Salmon's " Higher Algebra " (3rd edition, p. 39). 

 The symmetrical form may be obtained from the one there given 

 by writing — 



