August 16, 1907] 



SCIENCE 



211 



tions, parallaxes, magiiitudes, and the type 

 of spectrum of stare 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 ara 

 known to astronomers and need not there- 

 fore be here repeated. In all respects save 

 one these proposals are practical and ade- 

 quate, and the required cooperation may 

 be said to be already 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 spectro- 

 scopes of comparatively low dispersion 

 -must be employed. On this account there 

 is great need in both hemispheres of a huge 

 reflecting telescope — 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 hemis- 

 phere. Let us hope that Professor Picker- 

 ing's appeal for a large reflector to be 

 mounted in the southern hemisphere will 

 meet with an adequate response, and that 

 it will be devoted there to this all-im- 

 portant work. 



CONCLUSION 



The ancient philosophere 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 unsupported 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 center of the universe, and the battle 



was fought as to what that center 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 oc- 

 eupation for twenty-five centuries. 



But astronomers now recognize that 

 Bradley's meridian observations at Green- 

 wich, made only one hundred and fifty 

 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 phe- 

 nomena of sidereal astronomy must be con- 

 tent to progress by the accumulating labors 

 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 discussed 

 observation than by the most brilliant 

 speculation; and that, in observation, con- 

 centrated systematic effort on a special 

 thoughtfully selected problem will be of 

 more avail than the most brilliant but dis- 

 connected work. 



By these means we shall learn more and 

 more of the wonders that surround us, and 

 recognize our limitations when measure- 

 ment and facts fail us. 



Huggins's spectroscope has shown that 

 many nebulse 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 nebulae consist of the 

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

 been and are being evolved. The different 

 types of star spectra form such a complete 

 and gradiial sequence (from simple spectra 

 resembling those of nebulse onwards 

 through types of gradually increasing com- 

 plexity) as to suggest that we have before 

 us, written in the cryptograms of these 



