AN AMERICAN ASTRONOMICAL ACHIEVEMENT. 449 



by the method I had described. This was nearly three months before 

 Secchi's paper appeared. Subsequently Huggins observed by this 

 method a number of stars, some of which he found to be receding 

 from us, others approaching us. 



Recently, however, the method itself has been called in question 

 first, by Van der Willigen, for reasons professedly mathematical, 

 but unsound ; secondly, by Secchi, because of his failure to see what 

 Huoforins has observed. Secchi had once based his attack on his fail- 

 ure to detect by this method the effects of the sun's rotation. As the 

 sun's equator is spinning swiftly round, it is necessarily approaching 

 on one side and receding on the other. By some amazing miscalcula- 

 tion, never yet explained, Secchi made the rate of this motion many 

 times larger than it really is so large, in fact, that the method we 

 have described should have exhibited the sun's whirling motion. 

 Small as the effect really is amounting, in fact, only to a relative 

 motion of about two and a half miles per second Huggins did not 

 despair of recognizing it ; but he failed, though he used a double and 

 twice-acting battery of prisms (the invention of the present writer 

 so far, at least, as its duplex character was concerned) made by Mr. 

 Browning. Mr. Christie, of Greenwich, after resolutely grappling 

 with the work of determining star-motions by this method, and in the 

 main confirming Huggins's results, succeeded in recognizing by its 

 means the known motions of Venus toward or from the earth, in vari- 

 ous parts of their respective orbits. This was a great triumph, and 

 more than met Secchi's objections. But Prof. Young has gone, for 

 the present, ahead of all other observers by this method. Availing 

 himself of a beautiful extension of spectroscopic powers, due to Dr. 

 Rutherfurd, of New York, he has succeeded in unmistakably recog- 

 nizing the effects of the sun's motion of rotation by the spectroscopic 

 method. Young has made the observations so satisfactorily that he 

 relies even upon the difference between his results and the measured 

 rate of the sun's rotation. He finds the sun's atmosphere (whence, of 

 course, the spectral lines come) to be traveling faster than the sun's 

 visible surface. To use his own words, "The solar atmosphere really 

 sweeps forward over the underlying surface, in the same way that the 

 equatorial regions outstrip the other parts of the sun's surface." The 

 difference of rate is about ten miles per minute. For my own part, 

 I doubt very much whether so small a difference can be indicated by 

 this method. But even if we regard this part of Young's work as 

 not yet proved nay, even if we go further, and accept nothing more 

 than the bare recognition of the sun's rotation by the new method 

 he must be congratulated on having effected the most delicate piece 

 of spectroscopic observation yet achieved by man. He has placed 

 beyond doubt or cavil a method of motion-measuring the most re- 

 markable yet invented, and likely, as instrumental means improve, to 

 be most fruitful in results of astronomical interest and importance. 

 vol. x. 29 



