212 



STELLAR PHOTOGRAPHY. 



were brought together, and every star found on either of the plates was looked 

 for on all the others. Residuals were next taken from the mean of the measures, 

 and exceeded three tenths of a magnitude in six cases only. One of these equalled 

 five tenths, the others four tenths of a magnitude. Another estimate was made in 



these cases, with results which are given in the remarks following Table IV. 



each of these cases, with results v 

 The mean of this estimate and that originally made has been employed in the table. 

 All of the measurements were made by Miss N. A. Farrar, and were entirely inde- 

 pendent, even in the case of the repeated stars. 



To determine the character of the spectra of the stars in the Pleiades, Plate 337 

 was taken on January 26, 1886. The exposure was 34 minutes, and the width of the 

 spectra was about 0.06 cm. The spectra of nearly forty stars of this group are shown 

 upon this plate, besides a large number of adjacent stars, since the region covered is 

 ten degrees square. Nearly all the brighter stars in the Pleiades have a spectrum 

 of the first type, in which the spectrum is covered by a series of well-marked lines 

 at regular intervals, including the lines C, F, G, h, and H of the solar spectrum. 

 The line K is wanting, or at least is too faint to be visible. 



The results are given in Table IV., in which 



ged in the ord 



of their photographic brightness. Stars leaving trails on all four plates are given 

 first, followed by those contained on three plates, two plates, and one plate, respect- 

 ively. The first column gives the number of the star in the Catalogue of Wolf pub- 

 lished in the Annales de l'Observatoire de Paris, Memoires, Tom. XIV., Deuxieme 

 Partie. This is followed by the designation employed by Bessel for the star, the 

 Durchmusterung number, the right ascension and declination for 1885, and the 

 mean photographic magnitude. No correction is applied for the error in the diam- 

 eter of the smallest diaphragm. The effect of diffraction would be to compensate 

 for this error. The uncertainty in this quantity, and also in the limiting magnitude 

 photographed, renders the magnitudes of the fainter stars somewhat doubtful. The 

 next column gives the residuals in tenths of a magnitude, found by subtracting 

 from the observed magnitudes on Plates 209, 248, 327, and 361 their mean values, 

 negative residuals being represented by Italics. The next column gives in the same 

 form the residuals found by subtracting the mean photographic magnitudes from 

 the results of the authorities indicated by the letters at the head of the column. 

 When the residual exceeds nine, it is indicated by a p if it is positive, and by an 

 n if it is negative. The exact value is then given in the notes following the table. 

 At the head of this column the letter a denotes the magnitudes found by Linde- 

 mann, Memoires Acad. Imper. St. Petersbourg, XXXII. No. 6, p. 22 ; b, observations 



