658 EEPOETS OF ASTKONOMICAL OBSEEVATOKIES, 



ferent observers, Mr. M. Mci^^eill and Mr. 'A. S. Flint, with tbree 

 different instruments, the Kahler transit and the Fauth transit (used 

 as zeuitli telescopes), and the prime vertical. The results agree re- 

 markably well, all giving the latitude between 40° 20' 57".76 and 40° 20' 

 57". 81, The final result is 40° 20' 57".79 ± 0". 04. In November, 1879, 

 a series of micrometrical observations were made ux)on the planet Mars 

 with the 0^-inch equatorial, for the purpose of fixing its i^olar compres- 

 sion. The reduction of the observations gives 2\q for the value of this 

 quantity: a result surprisingly accordant with that deduced theoreti- 

 cally by Adams, on the supposition that the law of density of the planet 

 is not very different from the earth's. Both satellites were readily seen 

 with the instrument, and this fact, with many others, goes to show that 

 the telescope, the object-glass of which it will be remembered has the 

 Gaussian curves, is one of the best, if not the best, of its size in exist- 

 ence. 



Occasional spectroscopic observations have been made; especially a 

 minute examination of the 70 dark lines in the solar spectrum given by 

 Angstrom and Thalen as belonging to the spectra of two or more 

 metals in common ; indicating, according to Mr. Lockter's ideas, the 

 existence of some common constituent in the metals concerned, and so 

 tending to show them to be really non -elementary. The examination 

 was made in the summer of 1881 with an apparatus of ur])recedented 

 dispersive power, consisting of a Rutherfurd grating of 17,000 lines 

 to the inch, and collimator and telescope of about 4 feet focus. As a 

 result, 5G lines of the 70 were found to be distinctlj' double or multiple; 

 7 were doubtful, generally because they could not be certainly iden- 

 tified, and 7 api)eared to be single; 3 of the 7, however, while shown 

 on the map as common to iron and some other metal, are not so given 

 in Thalen's tables. On the whole, it is clear that the facts brought 

 out do not favor Lockyer's hypothesis. 



One remarkable solar prominence was observed in October, 1881, 

 which in an hour reached an elevation of 350,000 miles — the highest yet 

 on record. 



The spectra of several comets have been observed, and some series of 

 observations have been made upon their places which have been of use 

 in computing their orbits. A few double-star measures have been 

 taken; and observations were made upon the transit of Mercury in 

 1878, the solar eclipse of last December, and sundry occultations. 



The solar eclipse of 1878 was observed at Denver by an expedition 

 sent out from Princeton, under the direction of Professors Brackett 

 and Young, and its results were duly published in the American Journal 

 of Science. 



Besides the members of the college classes, several others have 

 availed themselves, for a longer or shorter period, of the opportunities 

 at Princeton for the study of practical astronomy. 



