March io, 1898] 



NATURE 



445 



posure of nearly twenty-five hours to the nebulous region around 

 Eta Argus, without the film of the photographic plate being 

 much darkened, but the conditions with a refractor are not 

 precisely similar to those which obtain in the case of a reflector 

 having a short ratio of focal length to aperture. 



It appears, however, from some photographs recently taken 

 by Mr. W. E. Wilson. F.R.S., and exhibited at the Royal 

 Astronomical Society, that the time of exposure needed by the 

 photographic plate to depict the greater part of the Orion 

 nebula may be considerably reduced. Mr. Wilson uses a re- 

 flecting telescope of twenty-four inches aperture, and ten feet 

 «ix inches focal length, constructed by Sir Howard Grubb, and 

 provided with his usual type of driving-clock and electrical 

 control. With this instrument, and an exposure of only forty 

 minutes, he has been able to produce a portrait of Orion's great 

 nebula w-hich, as regards structural detail, will bear comparison 

 with any previously obtained. Good photographs of the Ojrigii 

 nebula and other nebulrehave also lately been taken at the^Paris 

 Observatory with exposures of an hour or less (see p 374) A 

 ■comparison of Mr. Wilson's photograph of the Orion nebula 

 with one recently taken by Dr. Roberts with the same exposure 

 ■shows that they both contain about the same amount of detail and 

 <xtent of nebulosity, so the decrease of the time of exposure is 



pencil in benumbed fingers, the crude outlines which have been 

 handed down to us as correct drawings of this wonderful 

 nebula, which we can now depict during four hours of clear sky 

 with far greater accuracy than is possible by the best hand-work 

 in a life-time" {Monthly Notices, R.A.S., vol. xlix. p. 207, 

 1888-89). 



The Spiral Nebula in Canes Venatici. 



The years 1888-89 will be marked with a white stone in the 



annals of celestial photography, for it was then that so many 



I remarkable proofs of its great capabilities were presented 



1 to the astronomical world. A photograph of the wonderful 



spiral nebula in the constellation Canes Venatici was obtained 



Fig 2. — Great Nebula in Orion. (From a photograph obtained by ; 

 Dr. Roberts, with an exposure of 7J hours.) 



probably to be accounted for by the use of more sensitive plates 

 than were formerly available. The central part of the Orion 

 nebula, as photographed in forty minutes, is here reproduced by 

 the side of a well-known drawing of the nebula lithographed by 

 Mr. L. Trouvelot in 1864, from drawings made by Prof. G. P. 

 Bond, of the Harvard College Observatory (Fig. 3). We have 

 thus what is undoubtedly the best drawing of the nebula com- 

 pared with a good photograph on the same scale (Fig. 4), and 

 though much of the fine detail in the latter picture has been 

 lost in reproduction, the difference between the work of the 

 hand and that of the photographic plate is very striking. 



Prof. Bond had to use every available hour for about five years 

 in order to determine accurately the structure and distribution 

 of the parts of the nebula. Such devoted perseverance cannot 

 but command admiration, yet, except for the satisfaction which 

 the celestial draughtsman derives from his work, a like expendi- 

 ture of time and energy would now be almost useless. It is not, 

 however, for the celestial photographer to depreciate the labours 

 of the plodding observer. As Dr. Roberts himself has said, 

 *'we ought, with all gratitude, to admire the patient, long- 

 suffering endurance of those martyrs to science, who, during 

 the freezing nights of many successive winters plotted, with 



NO. 1480, VOL. 57] 



Fig. 3. — Bond's drawing of the Great Nebula 

 in Onon {185^63). 



by Herr von Gothard in 1888 {Astronomische Nachrichten, No. 

 2854, 1888), and by Dr. Roberts in April, \^%^ {Monthly Notices, 

 A'.A.S., vol. xHx. p. 389, 1888-89). Dr. Common appears to 

 have taken a good photograph of the nebula in 1883, but he did 

 not publish any description of it at the time [Observatory, vol. 

 xi. p. 393, 1888). An accurate picture of the object was cer- 

 tainly much needed. The nebula had been drawn by Herschel, 

 Rosse, Lassell, and numerous other astronomers, and its con- 

 volutions had been more or less symmetrically traced. But 

 so long as only drawings, differing widely from one another, 

 existed of the spiral nebula in Canes Venatici, little was learned 

 about ;^the physical nature of the object. The photographs 



Fig. 4. — Photograph of the Great Nebula in Orion, 

 obtained with an exposure of forty minutes. 



showed that the whorjs of nebulosity were knotted with bright 

 spots — stars in the course of formation — and these followed so 

 closely the trend of the streams of nebulous matter, that their 

 connection with it was placed beyond the possibility of doubt. 

 The picture is a striking view of a stage of progress in the 

 evolution of stellar systems ; it exhibits in a most unmistakable 

 manner a "fluid haze of light" eddying into worlds, and 

 enables us almost to see cosmic processes at work. In the 

 accompanying illustration the nebula, as observed with Lord 

 Rosse's six-foot telescope and drawn by hand, is represented 

 (Fig. 5) side by side, and on the same scale, as a photograph of 

 the object obtained by Mr. Wilson with an exposure of forty 



