230 POPULAR SCIENCE MONTHLY. 



result was the discovery of the planet upon more than a score of plates 

 taken at various times during the preceding ten years. New stars 

 were formerly supposed to be of very rare occurrence, but since the 

 Harvard system of photographing the heavens has been introduced, 

 no less than three have been known to break out. 



The great revelations of our times have come through the applica- 

 tion of the spectroscope to the measurement of motions in the line 

 of sight from us to a star. No achievement of the intellect of man 

 would have seemed farther without the range of possibility to the 

 thinker of half a century ago, than the discoveries of invisible bodies 

 which are now being made with this instrument. The revelations of 

 the telescope take us by surprise. But, if we consider what the thinker 

 alluded to might regard as attainable, they are far surpassed by those 

 of the spectroscope. The dark bodies, planets, we may call them, 

 which are revolving round the stars, must be forever invisible in any 

 telescope that it would be possible to construct. They would remain 

 invisible if the power of the instrument were increased ten thousand 

 times. And yet, if there are inhabitants on these planets, our astrono- 

 mers could tell them more of the motions of the world on which they 

 live than the human race knew of the motions of the earth before 

 the time of Copernicus. 



The men and institutions which have contributed to this result 

 are so few in number that it will not be tedious to mention at least the 

 principal actors. The possibility of measuring the motions of the stars 

 in the line of sight by means of the spectroscope was first pointed out 

 by Mr. now Sir William Huggins. He actually put the method into 

 operation. As soon as its feasibility was demonstrated it was taken up 

 at Greenwich. In these earlier attempts, eye methods alone were used, 

 and the results were not always reliable. Then spectrum photography 

 was applied at the astrophysical observatory at Potsdam by Vogel. 

 Thence the photographic method soon spread to Meudon and Pulkova. 

 But, as often happens when new fields of research are opened, we find 

 them ablaze in quarters where we should least expect. The successful 

 application of the method requires not only the best spectroscope, but 

 the most powerful telescope at command. Ten years ago the most pow- 

 erful telescope in the world was at the Lick Observatory. Mr. D. 0. 

 Mills put at its eye end the best spectograph that human art could 

 make at that time, the work of Brashear. It is Campbell, who, with 

 this instrument, has inaugurated a series of discoveries in the line in 

 question which are without a parallel. 



A mere survey of what has been done in the various lines we have 

 mentioned would be far from giving an idea of the real significance 

 of the advance we are considering. Cataloguing the stars, estimating 

 their magnitudes, recording and comparing their spectra and deter- 



