OP ARTS AND SCIENCES. 



271 



vations will hereafter form a most valuable test of the correctness of 

 any assumed law, since in many cases they precede by more than half 

 a century any other observations of these stars of the same degree of 

 precision. This is shown in Table 11., which gives in successive col- 

 umns the name of the star, the number of observations contained in 

 Table I., the year in which the variability was discovered, and the 

 number of years by which this followed the observations of Her- 

 schel. A dash is inserted when the discovery preceded the observa- 

 tions. In these cases the observations of Herschel have less value, 

 since we iiave contemporaneous or antecedent observations which serve 

 to determine the nature of the changes. The last three columns give 

 the period in days, and the magnitude at maximum and minimum, 

 according to the catalogue of Professor Schonfeld.* 



TABLE II. 



The individual stars will now be considered in turn, so far as the 

 material exists for a more complete reduction than is given in 

 Table I. 



rj Aquilce. — The variation in light of this star has been discussed 

 by Argelander.f A light curve is given by which the brightness at 

 any time may be expressed in terms of an arbitrary scale of grades. 

 This scale is defined by expressing in grades the light of the compari- 

 son stars used in determining the changes in brightness of the variable. 

 Points have been constructed for each of these stars, with grades as 

 abscissas, and the photometric magnitudes as ordinates. A straight 



* Zweiter Catalog von vcriinderlichen Sternen. Mannheim, 1875. 

 t Astron. Nach., xix. 399. 



