12 



Herman Schultz, 



focal-adjustment under different temperatures has, at the different seasons 

 of the year, been found necessary, and I am certain that no serious errors 

 of this kind have presented themselves during the observations. 



In the work referred to I have given a detailed account of the two 

 parallel -wire-micrometers employed (I and II), of the reasons for procuring 

 the new micrometer, of the advantages possessed by microm. II over the 

 older one, of the examination of the micrometers, etc. Micrometer I was 

 used up to 1868 May 9 (night 215), and micrometer II was first used in 

 observation Aug. 11 (night 216) of the same year. As regards micrometer 

 I, here, as in the reduction of 20 Vulp., care was taken to determine the 

 coincidences made use of nearly in the same position of the screw as in 

 the corresponding observations. In the reductions of the observations, made 

 with microm. II, the corrections given loc. cit. p. 24 for the different breadth 

 of the threads of the screw have been employed here also. It is tolerably 

 clear, that these corrections depend more on the mounting of the screw 

 than on any really existing difference in the breadth of the threads. It is 

 also shown (loc. cit. pp. 21 — 23), that the corrections due to the form of the 

 threads are extremely small and accordingly of no practical consequence in 

 the reduction of the observations. The values of a single revolution of the 

 screws here made use of are (loc. cit. p. 26) respectively 



For micrometer I 17",230 



— micrometer II 12",887. 



The observations have not indicated any variation in the value of a revo- 

 lution for differences of temperature. 



The timekeeper used throughout the whole series of observations is a 

 Chronometer by Kessels N:o 1329. It is adjusted to sidereal time and beats 

 half-seconds. 



RESULTS OF THE AUTHOR S OBSERVATIONS. 



This section of the work presents the tables of the differential coordi- 

 nates resulting from each several evening's observations which constitute 

 the main matter in the present communication, preceded by such tables and 

 notices as are necessary for their illustration. These are followed by three 

 notes — note I containing an approximate catalogue of the right ascensions 

 and declinations of the stars of comparison; note II different supplementary 

 details of observation; and lastly note III a table of the nights of observation. 



