EEPOETS OF ASTRONOMICAL OBSERVATORIES. GG7 



and lol'^' 10' X. P. D. as have not been observed liere three times in 

 both ri<>ht ascension and declination. 



G. Stars nsed in observations of comets with the LMJ-iiich and U.d-inch 

 equatorial. 



7. Stars nsed in the determination of latitude by the United States 

 Coast and Geodetic Survey, the Lake Survey, Capt. G. M. Wueeler's 

 Survey, and by Lieut. Conunander Y. M. Greeis' in surveys in the West 

 Indies. 



Tbe whole number of observations made with the transit circle since 

 the last report is 4,140. Of these observations, 08 weic of the sun, 02 

 of the moon, 145 of the major planets, and ll") of the minor planets. 



The printing of the annual volume for 1870 has lieen delaytMl several 

 months by lack of fuiuls, but it is now nearly d()iu\ Of the transit 

 circle Avork, that for 1877 is ready for the })rint(M': the reductions of the 

 1878 observations are nearly hnished ; those of 1879 are nearly tinished 

 to apparent i)lace ; while those of 1880 are as lav advanced as the na- 

 ture of the w^ork Avill permit. 



The d.G inch equatorial. — This instrument is under the direction of Prof. 

 J. R. EAST3IAN, who has the same assistants as on the work with the 

 transit circle. It has been emi)loyed in the observations of comets and 

 occultations of stars, and also in determining tlie apjtroximate correc- 

 tions to the ephemerides of such minor planets as are not rea<lily found 

 with the transit circle. 



The meteorologi(;al department is under the direction of l*rofessor 

 Eastman, and tlie usual observations, at intervals of three hours, 1)e- 

 giuningat midnight, have been made throughout the year by the watch- 

 men, Messrs. Hays, JIoeigan, and Cahill. 



Astronomical photographii. — The experiments in astronomical i)hoto- 

 graphy, including the reduction of the i^hotographii! observations of the 

 transit of IMercury in May, 1878, are under the charge of Prof. Wm. 

 H ARKNESS, who has been assisted by Master E. F. Qualtrough and by 

 Mr. Joseph A. Kogers. 



At the date of my last report the reductions of the Ann Arbor photo- 

 graphs of the transit of Mercury were suspended because the reticule 

 l>hite used in making the pictures had not been returned to this obser- 

 vatory. Since then the plate has been received, and the work of reduc- 

 ing the i>hotographs has made considerable progress. 



An investigation has just been commenced for the purpose of obtain- 

 ing some light on the following questions, namely : 

 • 1st. What are the capabilities of objectives of various sizes for as- 

 tronomical photography, and what are the ajjproximate exposure coefli- 

 cieuts for the different classes of celestial objects"? 



2d. What form of an ai)paratus is best adapted for photographing 

 the corona during total solar eclipses, and what exposure coefficient is 

 likely to be required ? 



3d. What kind of pyroxylene is best adapted for astronomical pho- 

 tography, and how can it be produced with certainty ? IMuch time has 

 been spent in planning these experiments, and in devising suitable 

 apparatus for executing them, and it is hoped that they will lead to 

 practical results. ^ 



Solar ecliines of July 20, 1878, and January 11, 1880.— The reports on 

 these eclipses have been collected into a volume (which is noticed else- 

 where). 



The first part of the Transit of Veims papers, embracuig the liistory 

 and general discussion, is in the hands of the printer, and the composi- 



