326 



NA TURE 



[August i, 1907 



situation in the southern hemisphere. Such an observ- 

 arory, energetically worked, with due attention to all 

 necessary precautions for the exclusion of systematic 

 errors, would conduce more than anything else to remedy 

 ill some degree that want of balance of astronomical 

 effort in the two hemispheres to which allusion has 

 already been made. But in designing the programme of 

 the work it should be borne in mind that the proper 

 duty of the meridian instrument in the present day is no 

 longer to determine the positions of all stars down to a 

 given order of magnitude, but to determine the positions 

 of stars which are geometrically best situated and of the 

 most suitable magnitude for measurement on photographic 

 plates, and to connect these with the fundamental stars. 

 For this purpose the working list of such an observatory 

 should include only the fundamental stars and the stars 

 which have been used as reference stars for the photo- 

 graphic plates. 



Such a task undertaken by the Carnegie Observatory, 

 by the Cape, and if possible by another observatory in 

 the southern hemisphere, and by three observatories in 

 the northern, would be regarded by astronomers of the 

 future as the most valuable contribution that could be 

 made to astronomy of the present day. Taken in con- 

 junction with the astrographic survey of the heavens now 

 so far advanced, it is .-in opportunity that if lost can 

 never be made good ; a work that would grow in value 

 year by year as time rolls on, and one that would ever 

 be remembered with gratitude by the astronomers of the 

 future. 



But for the solution of the riddle of the universe much 

 more is required. Besides the proper motions, which 

 would be derived from the data just described, we need 

 for an ideal solution to know the velocity in the line 

 of sight, the parallax, the magnitude, and the spectrum- 

 type of every star. 



The broad distinction between these latter data and 

 the determination of proper motion is this, that whereas 

 the observations for proper motion increase in value as 

 the square of their age, those for velocity in the line of 

 sight, parallax, magnitude, and type of' spectrum may, 

 for the broader purposes of cosmical research, be made 

 at any time without loss of value. We should therefore 

 be most careful not to sacrifice the interests of the future 

 by immediate neglect of the former for the latter lines 

 of research. The point is that those observatories which 

 undertake this meridian work should set about it with 

 the least possible delay, and prosecute the programme 

 to the end with all possible zeal. Three observatories in 

 each hemisphere should be sufHcient ; the qualitv of the 

 work should be of the best, and quality should not be 

 sacrificed for speed of work. ' 



But the sole prosecution of routine labour, however 

 high the ultimate object, would hardly be a healthy con- 

 dition for the astronomy of the immediate future.' The 

 sense of progress is essential to healthv growth, the 

 desire to know must in some measure be' gratified. We 

 have to test the work that we have done in order to be 

 sure that we are working on the right lines, and new 

 facts, new discoveries, are the best incentives to work. 



For these reasons Kapteyn, in consultation with his 

 colleagues in diffeient parts of the world, has proposed 

 a scheme of research which is designed to afford within 

 a comparatively limited time a great augmentation of 

 our knowledge. The principle on which his programme 

 is based is that adequate data as to the proper motions, 

 parallaxes, magnitudes, and the type of spectrum of stars 

 situated in limited but symmetrically distributed areas of 

 the sky, will suffice to determine many of the broader 

 facts of the constitution of the universe. His proposals 

 and methods are known to astronomers and need not 

 therefore be here repeated. In all respects save one these 

 proposals are practical and adequate, and the required 

 cooperation may be said to be alreadv secured — the excep- 

 tion is that of the determination of motion in the line 

 of sight. 



.All present experience goes to show that there is no 

 known satisfactory method of determining radial velocity 

 of stars by wholesale methods, but that such velocities 

 ■must be determined star by star. For the fainter stars 

 huge telescopes and spectroscopes of coniparntively low 



NO. 1970, VOL. 76] 



dispersion must be employed. On this account there is 

 great need in both hemispheres of a huge reflecting tele- 

 scope — six to eight feet in aperture — devoted almost 

 exclusively to this research. Such a telescope is already 

 in preparation at Mount Wilson, in America, for use in 

 the northern hemisphere. Let us hope that Prof. Picker- 

 ing's appeal for a large reflector to be mounted in the 

 southern hemisphere will meet with an adequate response, 

 and that it wnll be devoted there to this all-important 

 work. 



Conclusion. 



The ancient philosophers were confident in the adequacy 

 of their intellectual powers alone to determine the laws 

 of human thought and regulate the actions of their fellow 

 men, and they did not hesitate to employ the same un- 

 supported means for the solution of the riddle of the 

 universe. Every school of philosophy was agreed that 

 some object which they could see was a fixed centre of 

 the universe, and the battle was fought as to what that 

 centre was. The absence of facts, their entire ignorance 

 of methods of exact measurement, did not daunt them, 

 and the question furnished them a subject of dispute and 

 fruitless occupation for twenty-five centuries. 



But astronomers now recognise that Bradley's meridian 

 observations at Greenwich, inade only 150 years ago, 

 have contributed more to the advancement of sidereal 

 astronomy than all the speculations of preceding centuries. 

 They have learned the lesson that human knowledge in 

 the slowly developing phenomena of sidereal astronomy 

 must be content to progress by the accumulating labours 

 of successive generations of men ; that progress will be 

 measured for generations yet to come more by the 

 amount of honest, well-directed, and systematically dis- 

 cussed observation than by the most brilliant speculation ; 

 and that, in observation, concentrated systematic effort 

 on a special thoughtfully selected problem will be of more 

 avail than the most brilliant but disconnected work. 



By these means we shall learn more and more of the 

 wonders that surround us, and recognise our limitations 

 when measurement and facts fail us. 



Huggins's spectroscope has shown that many nebulae 

 are not stars at all ; that many well-condensed nebulae, 

 as well as vast patches of nebulous light in the sky, are 

 but inchoate masses of luminous gas. Evidence upon 

 evidence has accumulated to show that such nebulje 

 consist of the matter out of which stars (i.e., suns) have 

 been and are being evolved. The different types of star 

 specfra forin such a complete and gradual sequence (from 

 simple spectra resembling those of nebulae onwards 

 through types of gradually increasing complexity) as to 

 suggest that we have before us, written in the crypto- 

 grams of these spectra, the complete story of the evolu- 

 tion of suns from the inchoate nebula onwards to the 

 most active sun (like our own), and then downward to 

 the almost heatless and invisible ball. The period during 

 which human life has existed on our globe is probably 

 too short — even if our first parents had begun the work 

 — to afford observational proof of such a cycle of change 

 in any particular star; but the fact of such evolution, 

 with the evidence before us, can hardly be doubted. I 

 most fully believe that, when the modifications of terres- 

 trial spectra under sufficiently varied conditions of 

 teinperature, pressure, and environment have been further 

 studied, this conclusion will be greatly strengthened. But 

 in this study we must have regard also to the spectra of 

 the stars themselves. The stars are the crucibles of the 

 Creator. There we see matter under conditions ol 

 temperature and pressure and environment, the variety 

 of which we cannot hope to emulate in our laboratories, 

 and on a scale of magnitude beside which the proportion 

 of our greatest experiment is less than that of the drop to 

 the ocean. The spectroscopic astronomer has to thank 

 the physicist and the chemist for the foundation of his 

 science, but the time is coming — we almost see it now — 

 when the astronomer will repay the debt by wide-reaching 

 contributions to the very fundamenta of chemical science. 



Bv patient, long-continued labour in the minute sifting 

 of numerical results, the grand discovery has been made 

 that a great part of space, so far as we have visible 

 knowledge of it, is occupied by two majestic streams of 

 stars travelling in opposite d'rrrt'or.s. .Accurate and 



