416 



PROCEEDINGS OP THE AMERICAN ACADEMY 



TABLE VII. 



of Table VII. None of them are given in the list prepared by Lord 

 Rosse of the stars not contained in the catalogue of Struve (Phil. Trans., 

 1868, p. 59). A comparison with the map of Mr. Common (Monthly 

 Notices, XLIII. 256) showed that Nos. 10 and 11 were already given 

 there. Mr. Common's stars 7if. 690 and np. 750 are not visible on G, 

 althouiih the first of them is well shown on F. The stars near Bond 

 685 and 741 were not measured on account of the nebulous light with 

 which they are surrounded. Their presence in G is somewhat doubt- 

 ful. Until the remaining stars are actually seen, we may infer that 

 they are too faint to be visible to the eye, and that our only evidence 

 of their existence is by means of the photographic jjlate. These stars 

 are also probably of a bluish color. As the number of stars is nearly 

 the same in the two parts of Table VI., we may infer that for white 

 stars the limiting magnitude for the photograph does not differ much 

 from that for the eye. 



The agreement of the results given on page 408 is hardly a fair test 

 of the errors of measurement. A better indication is afforded by the 

 repetition of the measurement of the red and blue stars in Table V. 

 The average difference in the results is .14 of a magnitude, which indi- 

 cates a probable error of each of about .08. The two measures of E 

 by Argelander's method and by sequences give for the Sij stars com- 

 })ared by both methods an average deviation of .20, or a probable error 

 of .12. Forty stars are common to E and F. Omitting the five 

 which are stated on page 413 to be discordant, the average difference 

 in the two magnitudes of the remaining thirty-five is .27. The proba- 

 ble error of each, if they are equal, is .16. 



