KNOWLEDGE & SCIENTIFIC NEWS. 



[April, 1904. 



ASTRONOMICAL. 



M. Ja.nsserv's Photogra.pKic Atla^s of 

 the Sun. 



Some twenty-eight years ag(i, M. Jansscn set on foot a 

 photographic study of the solar surface at the Meudon Obser- 

 vatory, of a somewhat special kind. His object was to obtain 

 the greatest possible sharpness of definition, and for this pur- 

 pose he had an objective constructed for him by I'razmowsUi 

 which brought the rays near the G line of the Fraunhofer 

 spectrum, and practically these alone, to a well-defined focus. 

 In conjunction with this instrument he used collodion plates, 

 sensitised by bromo-iodide, in which the iodide predominated, 

 with a small range of sensitiveness which corresponded to the 

 region of the spectrum for which the object glass had been 

 constructed. The photographs were therefore obtained 

 almost by monochromatic light, and were exceedingly' sharp. 

 The objective employed had an aperture of 0-135 metres and 

 focal length of 2 metres, a secondary magnifier enlarging the 

 image of the sun in the telescope some 15 diameters. Some 

 of the most characteristic and best defined from the store of 

 over 5ooo negatives which have now been accumulated at the 

 Meudon Observatory have been reproduced, enlarged four 

 times from the originals, in a superb atlas, recently published 

 by M. Janssen. These plates, 30 in number, and 21 inches by 

 i<S in size, are on a scale of about 4 feet to the solar diameter, 

 and show the intimate structure of the solar surface with a 

 minuteness and detail never seen in any previous publication; 

 the minute granulation of the surface and the dift'ercnt forms of 

 the reseau photospherique being most admiralily illustrated. 



Some Peculiarities of Comets* Tails. 



In an article in " Popular Astronomy," illustrated by a 

 number of beautiful photographs. Professor Barnard draws 

 attention to some peculiarities apparent in the photographs 

 of some recent comets which do not seem to be sufficiently ex- 

 plained by the well-known theory of Professor Bredikhine of 

 the repulsive action ex-ercised by the sun upon the cometary 

 nucleus. The comets specially remarked upon are those of 

 Swift, 1902 : Brooks, 1893 ; and liorrelly, 1903. The remark- 

 able way in Avhich the tail of Brooks' Comet was contorted and 

 broken on October 22, 1893, seems to clearly indicate that it 

 had encountered some resisting or disturbing medium. The 

 case of Borrclly's Comet was not less remarkable, but of a 

 diflerent kind. Here a tail, itself apparently uninjured, was 

 sec'U at a distance from the head. In this case there seems to 

 have been a slight but sudden change in the direction of the 

 emission of matter from the comet's head, thus cutting off the 

 supply from the first formed tail. The detached tail, however, 

 showed no clear evidence of acceleration in its motion, and 

 this would suggest that the sun had little to do with its flight 

 into space. 



Radial Velocities of Twenty StaLrs of the 

 Orion Type. 



Amongst the Decennial Publications of the University of 

 Chicago IS a Memoir by Messrs. Edwin B. P'rost and Walter 

 S. .-Vdams upon the motions in the line of sight of twenty stars 

 of the Orion type. The photograjihs of these spectra were 

 obtained with the Bruce spectrograph attached to the great 

 refractor of the Yerkes Observatory. I'he comparison spectrum 

 was always that of titanium, and sometimes, in addition, iron 

 or chromium, or else a helium tube wliich also gave the 

 hydrogen lines. The absolute velocities of the twenty stars 

 observed was evidently very small, and when corrected for the 



solar motion gave 7 kiloiuitri-- a second as the mean of the 

 twenty radial velocities. The proper motions of these twenty 

 stars (not their i-lciI radial velocities, as Professor Frost's 

 memoir has been curiously niisreadi are exceedingly small ; 

 the mean for nineteen of them only being o"oi5 on a great 

 circle, which is much smaller than for solar stars of corre- 

 sponding brightness, and indicates that the Orion type stars 

 are, as a class, very remote. A classification of thirty-one 

 stars of the type is given at the end of the paper, according to 

 the character of the lines of helium, silicon, nitrogen, and 

 o.xygen in their spectra. 



The Starrs of Secchi's Fourth Type. 



Another of the Decennial Publications is a Memoir by Pro- 

 fessor Haleand Messrs. EUerman and Parkhurst onthe spectra 

 of stars of the type of 152 Schjellerup, the Fourth Type of 

 Secchi's classification. The spectra of eight stars were 

 examined, and some most important conclusions reached. A 

 great number of bright and dark lines were detected over and 

 above the violet flutings of cyanogen, and the flutings of the 

 Swan spectrum. Of the dark lines, a large number were 

 measured, showing the presence of carbon, hydrogen, mag- 

 nesium, sodium, iron, calcium, and other metals recognised m 

 the sun. The carbon and metallic vapours appear to be very 

 dense, and to lie immediately aliove the photosphere ; above 

 these dense vapours are others giving rise to the bright lines, 

 of which about 200 are present. None of these could be 

 identified with certainty, but a few may possibly correspond 

 to the bright lines of the W'olf-Rayet stars, which the Fourth 

 Type spectra resemble in some other characteristics. Many 

 lines widened in sunspots are represented by strong dark lines, 

 suggesting that these stars may be largely co\ered by spots 

 akin to those of our sun. Some twenty per cent, of the Type 

 appear to be variable, exceeding the proportion observed in 

 the case ofThird Type stars. Professor Hale suggests that the 

 Third and Fourth types should be classed together as pro- 

 bably having developed from stars like the sun through loss of 

 heat by radiation. 



ZOOLOGICAL. 



The Colours of Lobsters and Prawns. 



ExPKKiMENTb uiidert.ikeii many years ago were belie\ ed to 

 demonstrate that the colouring of Crustacea was largely, if not 

 entirely, of a protective nature. F"or instance, when prawns 

 or young lobsters were placed, in broad daylight, on black 

 dishes, the pigment-bearmg bodies, or " chromatophores," 

 in their integument were observed to expand, with ihe result 

 that a dark type of coloration in harmony with the tone of 

 the surroundings was produced. Conversely, when the 

 creatures were placed on a white dish, the pigment bodies 

 contracted, with the resulting production of a pale tone of 

 coloration, harmonising so tar as possible with the back- 

 ground. Moreover, if the crustaceans were deprived of sight, 

 no such adjustment of colouring occurred, although it took 

 place immediatelv that vision was restored. 



From these and other experiments, it has become the cur- 

 rent opinion that the pigments of crustaceans are superficial 

 and sporadic in distribution, that they are confined to single 

 cells— chromatophores — of the epidermal or connective 

 tissues, and that they are either protective in function or form 

 a waste functionless product of development. 



Recently, the subject has been taken up anew by Messrs. 

 Keeble and Gamble, the results of whose investigations 

 appear in the Philosophical Tnuisiutiuiis of the Royal Society. 

 While fully recognising the paramount influence of background 

 on the colours of crustaceans, the authors find themselves 

 compelled to adopt an attitude of reserve and indecision in 

 regard to most ol the foregoing points. They state, for in- 

 stance, that even the protective function of colour is not 

 definitely determined by experiment : while pigment in crus- 

 taceans may be deep-seated, and may also occur in complex 

 organs not 'functionally related to one another, l-'urther in- 

 vestigation is necessary before anything definite can be 

 predicated as to colour-function in these creatures. 



