208 



Prof. C. Pritcliard. 



Table V. 



Star. 



No. 7 . 

 » 8. 

 » 9- 



» io. 



„ 12. 

 „ 13. 

 „ 15. 

 „ 24p 

 » 17. 

 » 18. 

 „ 19. 

 „ 20. 

 22. 



Mean deviation 



On 



photograph. 



0-16 

 0-22 

 0-05 

 0-38 

 0-36 

 0-05 

 0-31 

 0-23 

 0-23 

 0'12 

 0-09 

 0-39 

 0-37 



In 



heliometer. 



23 

 0-27 

 23 

 0-11 

 0-19 

 0-19 

 0-20 

 0-26 

 0-33 

 0-18 

 0-71 

 0-43 

 0-43 



Star. 



No. 24 , 

 „ 27. 

 „ 29. 

 „ 30. 

 „ 31. 

 „ 32. 

 „ 33. 



Merope 

 Maia . . 

 Atlas . . 

 Pleione 

 26s 



Mean deviation 



On 

 photograph, 



027 

 0-18 

 0-03 

 0-32 

 0-48 

 0-17 

 0-45 



0-24 

 0-31 

 0-13 

 0-28 

 0-24 



In 



heliometer. 



0-20 

 0-11 

 25 

 0-47 

 0-36 

 0-37 

 0-42 



# 

 # 



* For these five stars, Bessel has not expressed the individual results in seconds 

 of arc. 



The average discordance for the entire group is in the case of photographic 

 measures , 24 // , and in the case of heliometer measures 0"29". 



In the above preceding clause I have adopted the term general mass, 

 because on one of the plates (fig. 2) there occurs a somewhat curious 

 and instructive fact, viz., that while for nineteen instances of stars 

 measured from tj Tauri, the distances agree with those of the same 

 stars on the other three plates, there is a sensible discordance between 

 the measures of Atlas, Pleione, Nos. 29, 31, 32, and 33, when com- 

 pared with the similar measures on the three other plates. This fact 

 indicates a distortion of the film at the places where these six stars 

 are impressed. On inspecting the diagram of the plate, it is observ- 

 able that all these six stars, exhibiting these discordances of distance 

 from 7], lie on the same portion of the plate. It follows, necessarily, 

 that three of the plates must accurately represent the portion of the 

 heavens impressed, and the fourth plate in those portions only which 

 exhibit an identity with the other three. From this fact we conclude 

 that it is not safe to regard any single plate as necessarily accurate 

 in itself, unless it is corroborated by the identity of exact measure- 

 ments, when compared with others also. The discordances here 

 referred to are small, but existent, perceptible, and in themselves 

 destructive of accurate astronomical conclusions involved therein. 



