34 



NATURE 



[ May 1 1 , i J 



ceeded in taking a very fine and extensive photograph o' 

 the nebula containing most of the delicate outlying parts 

 which were not in my earlier photographs. This is in the 

 hands of the photolithographer now and will shortly be 

 published. The experiments have been very difficult be- 

 cause an exposure of more than two hours in the telescope 

 has been necessary, and an exceedingly minute motion of 

 the stars relative to the sensitive plate will become apparent 

 on account of the high magnifying power (180) employed. 

 In carrying out the second object two contrivances 

 have been used ; first, a direct-vision prism in the cone 

 of rays from the objective before they had reached a 

 focus, and second the two-prism spectroscope with which 

 I have taken photographs of stellar spectra for some 

 years past. 



During the month of March I have made two good 

 photographs with each of these arrangements. Those 

 with the direct-vision prism, without a slit, have of course 

 demanded that the image should be kept stationary on 

 the sensitive plate throughout the exposure, viz. two 

 hours, and they are as difficult to get as good photographs 

 of the nebula itself. On the contrary, those obtained with 

 the slit spectroscope do not require the same steadfast 

 attention. 



The results derived from these photographs are inter- 

 esting partly from what they show and partly from what 

 they promise in the future. A number of photographs, 

 under various conditions, will be needed for the full 

 elucidation of the subject. 



The most striking feature is perhaps the discovery of 

 two condensed portions of the nebula just preceding the 

 trapezium, which give a continuous spectrum. At those 

 places there is either gas under great pressure or liquid or 

 solid. I have not been able to detect any stars of sufficient 

 magnitude in these portions to produce this effect either 

 in my photographs of the nebula or in any of the well- 

 known drawings of this object. It seems to me also that 

 the photographs show evidence of continuous spectrum 

 in other parts of the nebula. In these respects the con- 

 clusions arrived at by Lord Rosse in his memoir (Pliil 

 Trans. Royal Society, June 20, 1867, p. 70) are to a certain 

 extent borne out. 



The hydrogen line near G, wave-length 4340, is strong 

 and sharply defined ; that at /;, wave-length 4101, is more 

 delicate, and there are faint traces of other lines in the 

 violet. Among these lines there is one point of difference, 

 especially well shown in a photograph where the slit was 

 placed in a north and south direction across the tra- 

 pezium ; the Hy line, X 4340, is of the same length as the 

 slit, and where it intersects the spectrum of the trapezium 

 stars, a duplication of effect is visible. If this is not due 

 to flickering motion in the atmosphere, it would indicate 

 that hydrogen gas was present even between the eye and 

 the trapezium. I think the same is true of the H8 line, 

 X 4101. But in the case of two other faint lines in this 

 vicinity, I think the lines are not of the length of the slit, 

 one being quite short and the other discontinuous. If 

 this observation should be confirmed by future photo- 

 graphs of greater strength, it might point to a non- 

 homogeneous constitution of the nebula, though dif- 

 ferences of intrinsic brightness would require to be 

 eliminated. 



The April number of the American Journal of Science 

 contains an account of a photograph of the spectrum of 

 this nebula taken by Dr. Huggins. I have not found the 

 line at X 3730, of which he speaks, though I have other 

 lines which he does not appear to have photographed. 

 This may be due to the fact that he had placed his slit 

 on a different region of the nebul2, or to his employment 

 of a reflector and Iceland spar prism, or to the use of a 

 different sensitive preparation. Nevertheless, my refer- 

 ence spectrum extends be\ond the region in question. 



As illustraring the delicacy of working required in this 

 research, it may be mentioned that in one of these photo- 



graphs the spectrum of a star of the tenth magnitude is 

 easily discerned. It is only a short time since it was 

 considered a feat to get the image of a ninth magnitude 

 star, and now the light of a star of one magnitude less 

 may be photographed, even when dispersed into a 

 spectrum. 



EPPING FOREST 



ON Saturday last, May 6, the Queen declared free 

 to the public the 5600 acres of open land to the 

 north-east of London, known as Epping Forest. The 

 history of the rescue of this magnificent tract, so long the 

 favourite resort of London naturalists, has been told many 

 times since the Corporation of London took up the ques- 

 tion, and by their well-directed efforts not only checked 

 the encroachment of rapacious land-owners, but restored 

 to the people about 1000 acres of forest land that had 

 been illegally inclosed. The total cost of this philan- 

 thropic movement may be estimated at nearly half a mil- 

 lion of money, and the Corporation has deservedly earned 

 the gratitude of all Londoners, and more especially of 

 those lovers of nature who have for long been in the 

 habit of regarding the Forest as a preserve from which 

 they could obtain materials for their studies. It is a 

 common complaint with our natural history students, that 

 the open spaces around London are gradually being de- 

 stroyed as the pressure of population necessitates increase 

 of buildings in the suburbs, so that the preservation of 

 this large area is really a matter of considerable scientific 

 importance, and as such will be regarded with satisfac- 

 tion by the readers of Nature. Fortunately for natu- 

 ralists, the Act of Parliament declares that the woodland 

 tract under consideration shall be kept as far as possible 

 " in its natural aspect." There has thus been secured to 

 the public at large, and to the metropolitan field natu- 

 ralists, a recreation-ground of a quite peculiar character, 

 and one which will be looked upon as a great boon by 

 botanists, zoologists, and microscopists. 



The value of Epping Forest, from our point of view, 

 lies chiefly in its wildness ; by far the greater portion is 

 primitive woodland, which has been but little interfered 

 with by man in comparison with the heaths and commons 

 to the north, west, and south of London. Such an ex- 

 panse requires little in the way of " improvement." The 

 Conservators have acquired a power of dealing with one 

 of the few surviving remnants of primaeval Britain, and 

 in the interests of that continually increasing class of the 

 public who devote themselves to the various branches of 

 out-door natural history, it is to be hoped that this autho- 

 rity will be exerted judiciously. We are disposed to 

 believe that the requirements of the ordinary holiday- 

 maker and of the field naturalist are in this case identical. 

 To be able to roam through many miles of wild forest is 

 as truly a pleasure and novelty to the former as it is a 

 necessity to the latter. From whichever side we view the 

 question of the conservation of the forest, any attempts to 

 destroy its natural features cannot but be deprecated, and 

 in view of the fate of so many of the open spaces round 

 London, this position cannot be too strongly emphasised 

 by those to whom the preservation of our rapidly- 

 disappearing natural history resorts is a matter of 

 importance. 



The problem of managing a tract of country which con- 

 sists of a large proportion of primitive forest and a smaller 

 proportion of land formerly under cultivation, so as to 

 comply with the conditions of the Act and with the re- 

 quirements of all classes of the public, is not so difficult as 

 might appear at first sight. It is not as though the 

 interests of field-naturalists in any way clashed with those 

 of the general public. We have here a wide expanse 

 pro delectatione populi, which is to be distinguished and 

 to be kept distinct from all other public spaces in the 

 vicinity of the metre polis by virtue of its forestal wildness, 



