38 



NATURE 



\_May 10, 1888 



journey was most dangerous. At this height it had 

 rained, and the snow had become so soft that they often 

 sank to the waist in it. In the rapid slopes, where they 

 were forced to descend zigzag, the snow slipped from 

 under their feet, but, after much care and fatigue, they 

 arrived at the Grands-Mulels. A good meal, a denser 

 air, and a milder temperature, soon restored them to their 

 usual health. Towards 7 o'clock they came to Cha- 

 mounix, where they received an enthusiastic welcome. 



It had thus been proved that it was quite possible to 

 live and make observations at those high altitudes. The 

 greatest danger is in the violent storms that burst almost 

 without notice, and which may become terrible tempests 

 against which any temporary observatory would not 

 stand. M. Richard says that the results of the observa- 

 tions will be published when the papers have been 

 inspected and classified. 



THE PHOTOGRAPHIC CHART OF THE 

 HE A VENS. 



\ \ J E reprint from the- Observatory for May the 

 * V following article by the editors: — 



The "Bureau du Comite international permanent pour 

 1'exe'cution photographique de la Carte du Ciel '' has 

 published, amongst other more technical papers relating 

 to this subject, one by Dr. Gill, of a very remarkable 

 character, to which we wish to draw attention. Most of 

 those who attended the Conference understood that the 

 work in contemplation was to make a photographic chart 

 of the heavens, to take pictures of the stars by photo- 

 graphy, showing, with the greatest care, the appearance 

 of the heavens as they are at the present time, in order 

 that at a future time these pictures might be used, by 

 comparison with other pictures taken under similar con- 

 ditions or directly with the sky, to determine the many 

 questions that could be dealt with in this way — to enable, 

 in fact, the astronomer of the future to have the sky of 

 his past and his present to deal with. That this was so 

 will be seen from a consideration of the three following 

 resolutions which were agreed to unanimously by the 

 Conference : — 



"1. The progress made in astronomical photography 

 demands that the astronomers of the present day should 

 unite in undertaking a description of" the heavens by 

 photographic means. 



" 2. This work should be carried out at selected stations, 

 and with instruments which should be identical in their 

 essential parts. 



"3. The principal objects are (a) to prepare a general 

 photographic chart of the heavens for the present epoch, 

 and to obtain data which will enable us to determine with 

 the greatest possible accuracy the positions and the bright 

 ness of all the stars down to a given magnitude (the 

 magnitude being understood in a photographic sense to 

 be defined) ; (#) to provide for the best means of utilizing 

 both at the present day and in the future the results of the 

 data obtained by photographic means." 



These were the fundamental resolutions ; others, 

 recommended by the two sections into which the Con- 

 ference divided, were adopted as explanatory of the first. 

 Amongst these was one in which it was decided to take 

 "a second series of plates down to the nth magnitude, 

 in order to insure greater precision in the micrometric 

 measurement of the reference-stars, and render possible 

 the construction of a catalogue." We have stated these 

 fundamental resolutions at length as bearing on the 

 question of a catalogue of stars, for the paper by Dr. 

 Gill contains the astounding proposition of cataloguing 

 no less than 2,000,000 stars ; that is to say, Dr. Gill 

 gravely and seriously proposes the establishment of a 

 Central Bureau, consisting of chief, assistants, secret- 

 aries, and a staff of measurers and computers, to take 

 the photographs and measure them, and make a catalogue, 



the work to go on for twenty-five years at a cost of" 

 250,000 francs, or ,£10,000, per annnm, or for fifty years 

 at 150,000 francs. 



It is quite true that this is only a proposition that 

 Dr. Gill makes ; but if such a proposition is possible in 

 face of these direct resolutions of the Conference, it is 

 quite time that everyone interested in the success of the 

 work the Conference met to consider (that is, the photo- 

 graphic chart of the heavens) should bestir himself and 

 see that the proposed work is not endangered by such 

 astounding proposals. 



To tack on to a work such as that sanctioned by the 

 Conference — a work eminently practical, that has the 

 support of all astronomers, and that has already been 

 taken up by many of the Governments who were expected 

 to join — a gigantic work such as Dr. Gill proposes, a work 

 beside which that proposed by the Conference sinks into 

 insignificance, would neither be fair to the Conference 

 nor just to those Governments who have joined in the 

 undertaking. The feature of the international scheme 

 that makes it possible to obtain the assent of Government 

 is that the work is proved to be practicable by experiment, 

 and that it can be done at a moderate cost in something 

 like five years, while the results are good for as long as the 

 plates will last. To increase this work by extending it to,, 

 at the lowest computation of time, twenty-five and possibly 

 fifty years, and to add enormously to the cost, would be to 

 jeopardize the whole scheme. 



Dr. Gill states that the actual state of astronomical 

 science demands a catalogue of stars to the nth magni- 

 tude. He thus raises the question on its merits ; and we 

 would here state that it is more than possible that not 

 only is there no need of such a catalogue, but that the use 

 of such catalogues as he proposes has for ever ceased. 

 The minds of some astronomers move in grooves, and it 

 will, no doubt, never be conceded by them that catalogues 

 can be superseded ; they will die as they have lived, in 

 the strong belief that the only way to use the stars is to 

 catalogue them. 



Till recently the knowledge we had of the stars was 

 only to be gained from a written description of their 

 brightness and position with regard to each other ; hence 

 the catalogue was an absolute necessity if we needed to 

 know the number or brightness of certain stars in any 

 part of the sky at any previous time ; and we could only 

 find this out if we had a catalogue of that time. Our 

 catalogues of stars are all we have to show what has been 

 observed up to the present time ; but when we have a 

 photographic chart of the heavens, we have for our record 

 not a catalogue, but a representation. That catalogues of 

 stars such as are used for fundamental places will be 

 always used goes without saying ; the photographic plates 

 themselves, and the four or five stars on each required as 

 the fiducial points and for identification, will of course be 

 catalogued ; but, beyond this, to catalogue the stars on 

 each plate, to measure them for the purpose only of getting 

 their places written down, would be the most utter waste 

 of time, labour, and money that it could enter the mind 

 of man to conceive. 



The proposition brought forward by Dr. Gill should be 

 settled decisively so far as the proposition concerns the 

 work proposed by the Conference. There can be no 

 question that such a thing was never intended ; had such 

 a thing been thought of, we should have had a " Conference 

 for discussing the best way of making a Catalogue of 

 Stars by photography." 



As this was not done, it can be done now ; and if there 

 is the great need of a catalogue of stars to the nth 

 magnitude felt by so many astronomers, as stated by 

 Dr. Gill, it is a thing of so mu:h greater importance as 

 far as cost and time are concerned, that it should be 

 considered and dealt with entirely apart from the other 

 work. A new Congress might discuss it ; the one which 

 met in 1887 is not in any way committed to such a scheme. 



