84 THE POPULAR SCIENCE MONTHLY. 



astronomical discovery, which has since been ascribed to Janssen, 

 who, later (though independently and by another method), effected it. 

 Prof. Cooke made a series of observations on those bands in the solar 

 spectrum which are due to our own atmosphere, with the object of 

 ascertaining whether they are due to the constant constituents of the 

 air, Or to the aqueous vapor which is present in the air in variable 

 quantity. Combining hygrometric with spectroscopic observations, 

 he found that when the air is moist these bands are more clearly seen 

 than when the air is dry, and by systematic observations so definitely 

 ascertained this relation as to prove beyond all manner of doubt that 

 the bands are due to aqueous vapor. Unfortunately, though his re- 

 sults were published in America, they were not published in such a 

 way as to attract notice in Europe, and accordingly European as- 

 tronomers remained ignorant of the most important fact discovered 

 by Cooke until they had rediscovered it for themselves. 



The observatory at Ann Arbor, Michigan, was erected in 1854, 

 chiefly through the exertions of Chancellor Tappan, of the Michigan 

 University. Dr. Brilnnow, our present Astronomer Royal for Ireland, 

 was for a long time director of this observatory. It is at present un- 

 der the able control of Prof. Watson, who has added nearly a score 

 of planetoids to the known members of the solar family. 



The observatory of Dartmouth College, Hanover, New Hampshire, 

 illustrates in a remarkable way the energy and zeal with which college- 

 observatories are managed in America. It would be difficult to name 

 any observatory in this country where observations of greater interest, 

 as respects the physics of astronomy, have been made than those 

 effected by Prof. Young with the nine-inch telescope constructed by 

 Alvan Clark for the Dartmouth College ; or than the supplementary 

 observations made by Young with a powerful telescope conveyed to 

 an elevated pass in the Rocky Mountains. Among his results may 

 be specially mentioned first, the observations of the most remarkable 

 solar outburst yet witnessed, an outburst during which the glowing 

 hydrogen of the prominences was driven to a height of at least 200,000 

 miles from the surface of the sun; and, secondly, the identification 

 of more than 250 lines in the spectrum of the solar sierra. 



And as the most interesting and characteristic observations yet 

 made upon solar prominences are due to Prof. Young, of Dartmouth 

 Observatory, so the most accurate and detailed drawings yet made 

 of sun-spots are those by Prof. S. Langley, of the Alleghany Observa- 

 tory, near Pittsburg. 



At Chicago, a very fine telescope, eighteen inches in aperture, by 

 Alvan Clark, has been erected ; but, owing to pecuniary difficulties 

 consequent on the great fire (followed by the commercial depression 

 which has recently affected the United States), that observatory has 

 suffered considerably from the want of a properly remunerated direc- 

 tor. The Astronomical Society of Chicago has done its best to set 



