September 23, 1898.] 



SCIENCE. 



387 



in general than the field of view of the 

 ordinary photographic telescope, and vastly 

 greater than that of a powerful visual tele- 

 scope. We want, therefoi'e, a short focus 

 instrument, one capable not only of taking 

 in a wide part of the sky, but also of giving 

 a brilliant image, or, in other words, the re- 

 duction of the large details to a smaller 

 scale, with a correspondingly great increase 

 of effective light-power. These conditions 

 exist in the large portrait lenses which 

 were needed in the early days of photog- 

 raphy to reduce the exposure time by col- 

 lecting a great quantity of light from the 

 object, and which in these days of rapid 

 dry plates are no longer required for por- 

 trait work. Taking in some ten or twelve 

 degrees of the sky, these lenses are spe- 

 cially suitable for photographing large sur- 

 faces, such as are presented by the Milky 

 Way. 



This subject was taken up by the writer 

 in the first part of 1889 at the Lick Obser- 

 vatory, with a large 6-inch portrait lens of 

 31 inches focus, and with it was inaugu- 

 rated the photography of the Milky Way. 

 The first picture to show the real structure 

 of the Milky Way was made in 1889, with 

 this instrument. In the few following 

 years a large series of photographs of those 

 portions of the Milky Way seen from the 

 northern hemisphere was made. The work 

 with similar instruments was next taken 

 up by Dr. Max Wolf, in Germany, who has 

 also succeeded in making excellent pictures 

 of the Milky Way. Mr. Eussell, of Sydney, 

 New South Wales, has also photographed 

 portions of the southern part of the Milky 

 Way, with a large portrait lens. Those 

 who have seen some of the Milky Way 

 photographs taken with the regular Astro- 

 Photographic telescope, or who have tried 

 to make out its complex structure with a 

 visual telescope, must be struck with the 

 great beauty of a photograph made with 

 one of these short focus portrait lenses. 



The extraordinary complexity of structure 

 of the Milky Way is brought out with 

 marvellous beauty of detail, and the pecul- 

 iarities of its different portions can be traced 

 and connected in the different photographs, 

 which thus afford the most direct means 

 for studying every feature of structure and 

 detail. These pictures show manj' pecul- 

 iarities which must materially alter our 

 ideas of the constitution and structure of 

 the Milky Way. Some of them show 

 strong evidence that the general body of the 

 Milky Way may be made up of small stars 

 which are not at all comparable with 

 our sun in dimensions. This is especially 

 shown in the region of the star Rho Ophiu- 

 chi. Many parts of the Milky Way appear 

 to be comparatively thin sheetings of stars 

 with relatively no very great depth, for it is 

 not possible otherwise to explain the black 

 holes and rifts shown in them. One of the 

 most important revelations made by the 

 portrait lens in connection with the Milky 

 Way is the presence in it of very diffused 

 nebulous matter apparently freely mixed 

 with the groundwork of stars, and seem- 

 ingly showing no definite tendency to 

 condensation about the individual stars. 

 These photographic nebulosities of the Milky 

 Way are apparently of a different nature 

 from the ordinary nebulse of the sky, since 

 they are extraordinarily large, diffused and 

 but feebly luminous. These nebulous re- 

 gions seem to be peculiar to the Milky Way 

 and its vicinity, and are certainly in some 

 way physically connected with it. It will 

 be in the study by photography of such re- 

 gions that we shall finally clear away some 

 of the mysteries of the Milky Way. These 

 masses of diffused nebulosity mainly affect 

 regions of the sky in Scorpio, Cygnus, 

 Cepheus, Perseus and Monoceros. I be- 

 lieve it to be true that no other form of 

 telescope but the old time portrait lens or 

 similar combination is capable of dealing 

 with these extraordinary objects. 



