Stars about j3 Gygni. 333 



plates it does not appear altogether necessary to adopt this process. 

 The interval between the dates of the plates is not long enough to 

 give a determination of parallax, even if it be desired to discuss 

 the observations with that object in view. Moreover, I know of 

 no reason for selecting as standard one set of distances rather than 

 another. The alternative would be to correct the scale values so 

 that the sum of all the distances on each plate would be equal to 

 the mean value of that sum. But a little consideration shows that 

 this would not change the final results. 



I have therefore set down in table V. the results of the measures, 

 in a form somewhat more condensed than that adopted for the 

 Pleiades.* It has appeared desirable to make it possible to return 

 to the original observations at any time, and the numbers in the 

 table are arranged in such a way that the separate observations of 

 the Eastern and Western impressions may always be made avail- 

 able. The first two columns give the numbers of the star and plate. 

 Then follow the observed distances, which are given in divisions of 

 the glass scale. The numbers set down are the fractional part of 

 the measured distance, the whole number of divisions being ordi- 

 narily the same as that given in the column corrected mean. Occa- 

 sionally the corrections have been' sufficient to change the whole 

 number of divisions, in passing from the observed distance to the 

 corrected mean. In that case we may expect that the number in the 

 observed distance column will begin with a 9, while the fractional 

 part of the corrected mean will begin with a 6. All the quantities 

 given in the columns headed observed are taken without change from 

 the observation books. The corrections for division error, which 

 have been added to the observed values, are given in the next 

 columns. They are expressed in units of the fourth decimal place. 

 The corrected mean is obtained from the observed values by using 

 the division error corrections as given, and apptying further the 

 tangent correction, and those for refraction and aberration. For 

 the position angles I have given the observed value for the Eastern 

 impressions, taken without change from the observation books. The 

 last column gives the final corrected mean position angle. It is 

 obvious that the observed values for the Western impressions can 

 be reproduced from the two quantities given, by the aid of the cor- 

 rections contained in tables II. and IY. It will be noticed that the 



* Compare Ann. N. Y. Acad., vi, p. 280, et seq. 



