EErORTS OF ASTROXOMICAL OBSERVATOEIES. 007 



and 1310 10' K r. D. as liave not been observed liere throe times in 

 both rifi'lit ascension and decHnation. 



0. Stars used in observations of comets with the 2(;-in('li and O.fi-iiieli 

 equatorial. 



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

 Coast and Geodetic Survey, the Lake Survey, Capt. ii. 31. Wiieei.eu's 

 Survey, and by Lieut. Commander F. M. GrJeen iu surveys iu the West 

 Indies. 



The whole number of observations made with the transit circle since 

 the last report is 4,140. Of these observations, (iS were of the sun, 02 

 of the moon, 1-15 of the major planets, ami 11.") of the miiKu- i)lanets. 



The printing- of the annual volume for 1870 has been delayed several 

 months by lack of funds, but it is now nearly done. Of the transit 

 circle work, that for ]S77 is ready for the ])rinter; the reductions of the 

 1878 observations are nearly tinished ; those of 1879 are nearly iinislu'd 

 to apparent j^lace ; while those of 1880 are as lav advanced as the na- 

 ture of the work will permit. 



TJic d.C) inch equdforiaJ. — This instrument is under the direction of Tiof. 

 J. E. Eastman, who has the same assistants as on the work with tlie 

 transit circle. It has been employed in the observations of coiiiets aiul 

 occultations of stars, and also in determining the ai)i)roximate correc- 

 tions to the e[)liemerides of such minor planets as are not readily found 

 with the transit circle. 



The meteorological department is under the direction of Professor 

 Eastman, and tlie usual observations^ at intervals of three hours, be- 

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

 men, Messrs. Hays, Hokigan, and Cahill. 



Astronomical photographij. — The experiments in astronomical photo- 

 graphy, including the reduction of the photographic observations of the 

 transit of Mercury in ]\Iay, 1878, are under the charge of ]*rof. W'si. 

 Haekness, who iias been assisted by Master E. F. Qualtrough and by 

 Mr. Joseph A. IJogers. 



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 

 plate used in nuiking the pictures had not been returned to this obser- 

 vatory. Since then the plate has been received, and the work of rediu> 

 ing the photographs has made considerable ]U"ogress. 



An investigation has just been conmienced for the puri)Ose 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 ai)proximate exposure coeffi- 

 cients for the difttrent classes of celestial objects? 



2d. What form of an a]>paratus is best adapted for ])hotographing 

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

 likely to be required ? 



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

 tography, and how can it be produced with certainty 1 Much 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. 



mar ccUpHes of July 29, 1878, and January 11, 18S0.— The reports on 

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

 where). , . ^1 T • ^ 



The first part of the Transit of Venus papers, embracing the history 

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



