June 15, 1911] 



NATURE 



537 



images of these stars as compared with the corresponding 

 apparent distance on the sky serves to furnish a determina- 

 tion of the scale of the plate, while the direction of the 

 line joining them serves to fix the orientation of the plate, 

 i.e. enables us to turn the plate round in its own plane, 

 so that the true N. and S. line may be placed exactly in 

 a truly horizontal, truly vertical, or, in fact, any other 

 desired direction. With these quantities correctly assigned, 

 either star will be sufficient to correlate the plate exactly 

 with the sky. In practice it is customary to refer to a 

 larger number of stars than two on each plate. Not only 

 are the determination of these necessary " plate constants " 

 strengthened thereby, but in the consistency with which the 

 photographic pictures reproduce the actual distribution of 

 the stars, we have a valuable check on our methods and 

 a test of the faithfulness with which also other features 

 on the sky are represented on the photographs. For the 

 Cape plates, the determination of the "plate constants," 

 i.e. of those elements which serve, as it were, for the 

 coordination of the isolated maps contained on each plate 

 with a general map of the whole, has been made to depend 

 on a number of stars on each plate varying, as a rule, 

 between 8 and 12. In all, 8560 stars, so far as possible 

 evenly distributed over the whole of the zone, were selected 

 as comparison stars. These stars constitute a framework 

 to which the detailed results derived from the photographs 

 may be attached, but the structure of which requires to be 

 independently built up. For such a purpose, photographic 

 methods have not as yet proved available, and recourse 

 was necessary to the older method of visual observing with 

 the meridian circle. From observations made in the years 

 1897-1900 with the transit circle an accurate catalogue of 

 these 8560 stars has now been formed, and has been 

 utilised for the purpose of standardising each of our 

 plates. The heavy arithmetical work involved in apply- 

 ing to each of our original measures more than two 

 millions in number, the derived correction to refer the 

 whole to a common standard is now rapidly proceeding, 

 and at the present time is about half completed. 



I have above referred to the catalogue of 8560 com- 

 parison stars as framework for the support of the more 

 extensive photographic catalogue. Such a framework, at 

 least on the basis on which the one was constructed, is 

 not entirely self-supporting, and it thus behoves us to 

 carefully consider its foundations and to ensure that they 

 possess the necessary solidarity. Not the least of the 

 important questions brought up for discussion at the last 

 meeting of the International Committee charged with the 

 conduct of the photographic work was that of the steps 

 to be taken for this purpose. It was recognised on all 

 sides that even the test existing meridian catalogues were 

 inadequate, and that they would have to be supplemented 

 by extensive additional observations. The main object of 

 the discussion was to secure the most extensive coopera- 

 tion from observatories provided with suitable meridian 

 equipment, and to classify the work in various grades of 

 accuracy, so that each establishment might devote itself 

 primarily to that branch for which its equipment was best 

 adapted, at the same time keeping in view the coordina- 

 tion of its work with the larger scheme. The resolutions 

 adopted have since been favourably received by meridian 

 observers, and we may look in the future to a systematic 

 organisation of meridian astronomy throughout the world, 

 the results of which, apart from the mere economic aspect, 

 cannot fail to be of the highest importance to science. It 

 may well be asked. What is the use of such a chart as 

 you have been describing? or, Will it repay the enormous 

 cost involved in compiling it? As regards its use, I 

 endeavoured to indicate in my address last year some of 

 the problems which awaited solution, and which serve to 

 inspire the astronomer in conduct of the lengthy routine 

 operations involved. These motives are, perhaps, for the 

 most part scientific and intellectual rather than utilitarian, 

 and it is possible, even probable, that to many of the 

 questions arising answers which will afford complete satis- 

 faction will not be forthcoming at least for a generation 

 or two to come. I think I am sufficiently voicing the 

 view of those who took part in the original discussions at 

 Paris when I state that they, as a body, attached greater 

 importance to the complete and thorough systematic record 

 of the phenomena prevailing during their own gpn^rntion 



NO. 2172, VOL. 86] 



than to the immediate interpretation of these phenomena. 

 It was felt to be a scientific duty, incumbent on them to 

 provide, so far as lay within their means and capacity, 

 data which should be beyond reproach. By this means 

 they were preparing the ground and planting the seed, 

 which they hoped would yield a rich crop of scientific 

 results, even though it should remain for their children's 

 children to reap the harvest. 



Much has already been attained. The ghosts which beset 

 the use of photography in relation to the science of exact 

 measurement have in a large measure been laid, and 

 photographic methods have now been successfully used for 

 some of the most delicate measurements ever attempted 

 even by direct visual operation. 1 have in mind such 

 questions as the determination of the distance of annual 

 parallaxes of the fixed stars, and of the parallax of the 

 sun, in connection with which, under the auspices of the 

 Paris conference, an extensive photographic campaign, 

 combined with visual methods, was undertaken on the 

 occasion of the near approach of the planet Eros in the 

 years 1900-1. The discovery of the latter planet was itself 

 a product of photography, while by similar means the 

 number of known minor planets has within the last few 

 years increased by leaps and bounds, until at the present 

 day they are nearly seven hundred in number. Photo- 

 graphy has also been prolific in the discovery of variable 

 stars and new stars, and the tracing of their light changes. 

 All these purposes will be greatly facilitated by the exist- 

 ence of a trustworthy chart or catalogue containing more 

 especially the fainter stars about which our exact know- 

 ledge hitherto has been almost non-existent. Time must 

 elapse before we may expect to be able to evaluate with 

 any certainty the slow changes of position due to the 

 proper motion, at least, in relation to the previously un- 

 catalogued faint stars ; but this is to-day one of the 

 greatest desiderata for the advancement of our knowledge 

 of the universe, and is one of the purposes for which the 

 photographic catalogue was primarily intended. By photo- 

 graphic methods and by cooperative effort throughout the 

 world alone has it been possible to collect evidence on a 

 sufficiently wholesale scale, so that already we are 

 beginning to feel the solution of some of the most profound 

 problems relating to the universe almost within our grasp. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Camhridoe. — The Public Orator, Dr. Sandys, spoke as 

 follows in presenting for the degree of Doctor in Science, 

 honoris causa, (i) Dr. G. E. Hale, director of the Solar 

 Observatory on Mount Wilson, California, and (2) Prof. 

 T. W. Richards, professor of chemistry in Harvard 

 Universitv : — . 



(i) Adest vir in republica maxima transmarina caeh m 

 orbibus observandis iam per annos plurimos inaximo cum 

 fructu exercitatus, qui Californiae sub caclo sereno, 

 montis Wilsonii in vertice e.xcelso, instrumentis novis 

 adhibitis, solis ipsius materiem exquisivit et stellarum 

 remotissimarum mutationes invcstigavit. Rerum caeles- 

 tium auguri tam perspicaci stellarum ipsas origincs 

 nebularum (ut aiunt) formae obscurae illustrant ; stellao 

 autem colore priitium candido, dcindc Havo. dcnique rubro 

 coruscantes, orbium illorum vitam per scriem cxoricntem, 

 maturescentem, deficientem indicant ; orbis dcnique terra- 

 rum noster quasi imago stellae est ex qua lumen calorque 

 iam dudum evanuerunt. Ncwtoni nostri in Opiicis dicilur 

 in montibus summis, supra nubcs densiores. in acre 

 maxime sereno et tranquillo, Stellas inclius posse 

 observari : ' gratulamur auguri nostro caelcsti quod Cali- 

 forniae in monte altissimo arccm nactus est, caelo 

 observando tam opportunam, unde orbis terrarum incolis 

 vallium et camporum in obscuritatc degentibus rerum 

 naturae lucem ipsam possit dcsuprr transmittere. Viro 

 tot titulis aliunde cumulate, etiam nostram coronam 

 libenter donamus. _ 



Duco ad vos astronomum insigncm, Gcorgiutn Ellery 

 Hale. 



(2) Filiam suam, aequore Atlantico a se divisam, 

 studiorum communium amore coniunctnm, mater alma 

 1 Newton's " Optics," Book I., part i., ad/inftn. 



