HALL, ABERRATION CONSTANT. 39 



In the Notices are given, also, the determinations of the places of a 

 number of comparison stars for asteroids and comets. Sev'cral of the 

 older graduates have told me that Briinnow made with this meridian 

 circle an elaborate series of observations of the Bradley stars, the records 

 of which he took to Europe for reduction, by permission of the fniversity 

 authorities. I cannot find out anything regarding such observations. 



Professor Watson, after taking charge of the observatory, seems to have 

 been interested in the construction of ecliptic charts and the discovery of 

 minor }»Ianets, and not to have made any regular use of the meridian 

 circle. It w^as employed by Professor Schaeberle, however, for the observa- 

 tion of latilude stars, Struve double stars, and planets. See reporl of 

 Professor Harrington to the Regents, 1881. A list of 155 stars ol3served 

 by Professor Schaeberle was printed in the ''Publications of the Wash- 

 burn Observatory." They were reduced, it is stated, differentially, but 

 none of the constants of reduction are given. 



After some experience at. the Naval Observatory under Professor East- 

 man, I became interested in meridian circle work, and on coming to this 

 place resolved to make such observations. A new micrometer was pur- 

 chased from the Repsolds, a chronograph from Saegmiiller, and a clock 

 from Howard. The object glass was taken to the Clarks' shop and a 

 spring was put in the cell to act against the glass. The instrument was 

 taken to pieces and carefully cleaned. Observations were begun of a list 

 of Bradley stars, including a number to be used for latitude at the George- 

 town College Observatory. 



On looking up the latitude of this place no record could be found of an 

 accurate determination, so that observations were made of Polaris, both 

 for the purpose of determining latitude and with the idea of obtaining the 

 amount of latitude variation at Ann Arbor. Also, an examination was 

 begun of the division errors of the fine circle, to test the permanency of 

 the values given by Dr. Briinnow. The reduction of the nadirs was kept 

 up, and they seemed to show that the instrument was steady and the 

 work good. During term time of the University it was necessary to 

 neglect the other reductions. As soon as they could be brought up the 

 work was shown to be not first rate. The reduction of the observations 

 of the Bradley stars are pretty well completed. They can be used, I think, 

 if they are made strictly differential. 



On looking the instrument over again the following trouble was found 

 which had probably existed since it was first mounted. To support our 

 meridian circle two brass cones with lugs attached are let into the stone 

 piers, and to the cones are screwed heavy brass discs. The discs support 

 the wye blocks which carry the pivots, and to the discs, also, are clam])('d 

 the microscope arms. The cones were found to be loose in their jtacking. 

 This packing was what seemed to be mortar mixed with brick dust, the 

 brick dust being added, I suppose, to make the mixture hydraulic. See 

 the older hand books of engineering under cements. The packing when 

 removed was a fine, dry dust. 



I attempted to mount the cones in the piers first with lead and then 

 with plaster of Paris. Finally Portland cement was used and with it 

 they seem steady. We are under obligations to Mr. Fecker, superintend- 

 ent of Warner and Swasey's instrument department, and to Messrs, 

 Warner and Swasey for the remounting of the instrument. Mr. Fecker 

 called my attention to the fact that the object glass cell fitted loosely in 



