120 



KNOWLEDGE 



[May 1, 1897. 



west, and from the southern temperate parts to the ex- 

 treme north, within ten degrees of the Equator. Two or 

 three of the Australian species have been found in New 

 Guinea, and probably more remain to be discovered. One 

 extends to Timor, where there are two other species. One 

 has been found in the Celebes and one in New Tiritain, and 

 fourteen are recorded from Tasmania ; }'et not a single 

 species is a native of either New Zealand or New Caledonia, 

 both of which countries are situated within the parallels 

 of latitude covered by Australia. Their dispersion in 

 Australia is very peculiar. A few of them range across 

 the country from east to west and north to south, whilst 

 others are exceedingly rare and local. The greatest 

 number of species is recorded from New South Wales, 

 where fifty-four species have been found, but only four of 

 them have not been found elsewhere ; whereas of the 

 forty-seven found in Western Australia, thirty-seven appear 

 to be confined to that region, and four of the fourteen 

 Tasmania species are peculiar to that island. \ 



THE NEBULA ROUND r, ARGUS. 



By E. Walter Mauxder, F.R.A.S. 



THEEE are some objects in the heavens which never 

 seem to lose their interest, liowever often they are 

 examined ; we can turn to them whenever an 

 opportunity for their observation occurs, and still 

 find their beauty fresh and their marvel and 

 mystery inexhaustible. To us Northerners the great 

 nebula in Orion holds an easy primacy amongst objects of 

 this class ; for our more fortunate brethren in the South, 

 its precedence is disputed by the nebula round the most 

 mysterious of variable stars, J'Ua, in the Keel of the Ship. 

 So, though we have already presented to the readers of 

 Knowledge no fewer than 

 seven illustrations of this 

 object within the last six 

 years, we feel sure that they 

 will welcome an eighth, es- 

 pecially one that can teach 

 us much by comparison with 

 its predecessors. 



Before referring to the 

 photograph it is necessary 

 to say a few words about the 

 telescope with which it was 

 taken, for it must be re- 

 mtuibered that not only is 

 there such a thing as " per- 

 sonal equation " for direct 

 visual work, but when we 

 enter the domain of photo- 

 graphic observation we have 

 to recognize systematic pecu- 

 liarities of more than one 

 kind, and especially what we may term an " instrumental 

 equation," depending on the class of instrument employed. 

 In this case the telescope was a very special one. So 

 long ago as 1883, Prof. E. C. Pickering, under whose direc- 

 tion the present photograph was taken, had pointed out the 

 greatusefulnes3,f'orcertainfieldsof research, of what is com- 

 monly spoken of as a portrait combination. And after having 

 recommended in vain the adoption of a doublet objective 

 for the work of the International Photographic Chart, Prof. 

 Pickering, in 18H8, appealed for a sum of fifty thousand 

 dollars in order to build such an instrument, with an 

 aperture of twenty-four inches and a focal length of eleven 

 feet. Miss Catherine W. Bruce, so well known, not only 



in her own country, but on both sides of the Atlantic, as 

 a most generous helper of astronomy, at once responded 

 to this appeal ; and in the autumn of 1889 the order for 

 the construction of the telescope was placed with Messrs. 

 Alvan Clark I'i; Sons, the rough discs being furnished by 

 Mantois. The instrument, when completed, was mounted 

 first at the Harvard College Observatory, Cambridge, 

 Mass. : it was then despatched, in the winter before last, 

 by sea to the astronomical colony which Prof. E. C. 

 Pickering has founded at Arequipa, Peru. Here Prof. 

 Bailey took the annexed photograph on June 1st, 189G, 

 with an exposure of four hours. Another photograph, 

 taken five days later with an exposure of sixty-two minutes, 

 and embracing the cluster N.G.C. C0G9, has, with the 

 photograph from which the accompanying plate has been 

 taken, been reproduced by photogravure, and Prof. Pickering 

 has distributed a number of the copies thus made, mostly to 

 observatories. A third photograph, which was taken on .June 

 11th, and which embraces the Trifid Nebula, appears in 

 Popular Astronomij for April. These reproductions afford 

 a significant testimony to the high value of the work 

 which Prof. Pickering has been enabled, by the munificent 

 liberality of Miss Bruce, to put in hand. And it opens a 

 wide field of research to astronomers who may possibly 

 possess no telescope themselves, and who may be quite 

 unable to travel to southern latitudes, for Prof. Pickering 

 contemplates furnishing contact prints on glass from the 

 original negatives — a method of reproduction far more 

 satisfactory than photogravure prints, for purposes of 

 scientific measurement and examination — to such astrono- 

 mers as will make use of them. 



It will be instructive to compare together the difi'erent 

 representations of this grand nebula that have appeared in 

 Knowledge at various times, and of which a list is given 

 in the following table :— 



The value of the first photograph lies, I think, rather 

 in the evidence it affords of the wonderful progress that 

 has been made in astronomical photography since it 

 was taken — i.e., in less than seven years — than in its 

 direct merit. Only little of the nebula is to be seen, a 

 circumstance commented on by Mr. Ranyard at the time 

 as showing that the nebula was deficient in actinic or 

 photographic light. The small scale of the photograph 

 prevents much detail being made out ; but, on the other 

 hand, the large field enables us to see the position and 

 bearing of the nebula with regard to its surroundings, and 

 the separation between the northern or " keyhole" portion of 

 the nebula and the southern portion is seen distinctly to 



