2 GOULD — REDUCTION OF D AGELET S OBSERVATIONS. 



Although the zone-observations of Lalande have been reduced and rendered conveniently- 

 accessible to astronomers — thanks to the suggestions of Bessel, the tables of Hansen and 

 Nissen, the liberal grants of the British Association, the industrious zeal of Bailt, and the 

 thorough accuracy of Fedorenko — still the observations of d'Agelet, though made at a date 

 anterior to any stellar observations of the modern school, save those of the incomparable Brad- 

 ley, have remained in their crude and almost useless form until the present day. I know of 

 no astronomer, excepting Argelander, who seems to have made use of them for more than 

 three-quarters of a century, and it was by this eminent astronomer that my attention was first 

 directed, more than twelve years ago, to the relatively' high value of these ancient observa- 

 tions. 



An examination of the originals soon convinced me that, if by any process the instrumental 

 errors could be eliminated, wo should have in these observations the best existing means of 

 determining proper motions for almost all the stars not observed by Bradley. Indeed, Arge- 

 lander, in his Positiones Media, has in several instances availed himself of d'Agelet' s obser- 

 vations for this purpose, doubtless by some differential process ; for the present discussion 

 of the original records has shown the determination of the instrumental corrections to bo a 

 work of such difficulty, that I can hardly imagine any other mode of procedure for isolated 

 stars. 



To the peculiar irregularities of these corrections, arising chiefly from a distortion of the 

 limb of the quadrant, I attribute the fact that these valuable observations have so long remained 

 in the crude state of ore, without any known attempts to extract the precious metal which they 

 contain. And, impelled by a strong desire to contribute to the Academy at its first scientific 

 session some memoir in the domain of practical astronomy, although destitute of any access to 

 astronomical instruments, I have thought that this could in no way be better accomplished than 

 by a discussion of the observations of d'Agelet, and the construction from them of a catalogue; 

 hoping that the work of rendering ancient observations available might not prove much less 

 serviceable than the attainment of new ones. 



Those portions of the computations which I have not made in person have been made at my 

 expense, and I desire to express my thanks to my pupils and assistants, Messrs. John N. Stock- 

 well, Erving Winslow, "William H. Palmer, S. C. Chandler, jr., and S. S. Eastwood, for 

 their valuable aid. Mr. Winslow has taken part in all the computations from the beginning. 



The catalogue contains G497 observations of 2907 stars situated between the parallels of 

 50° north and 35^° south declination. 



§ -2. HISTORICAL. 



The greater part of what we know of the astronomer to whom these observations are due 

 we derive from notices given by Lalande, and any attempt at a scientific biography of d'Agelet 

 can result in little more than a digest of what we there find, with such additional facts as may 

 be discovered by following up the clues there given. In spite of this circumstance it seems 

 desirable to give a summary of what is known concerning this zealous and devoted follower of 

 science. 



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