278 PROCEEDINGS OP THE AMERICAN ACADEMY 



Star of Class V. given in Birmingham's Catalogue is P Persei, and many 

 observers may be surprised that this should have been called a red 

 star. It is remarkable that but one star of short 25eriod, U Saglttarii, is 

 called red. On the other hand, six of the variables of long period are 

 given in the catalogue, including all of those wiiich have shown marked 

 discrepancies. Excluding these disposes of the large deviations, 66° 

 and 34°, in column three; and we find no star more distant than 16° 

 from the assumed plane in which the variables lie. Again, the large 

 discrepancies of the last column but one are removed, and T Monoce- 

 rotis probably placed with the variables of the fourth class. This view 

 is confirmed by the light curve given by Schonfeld, page 32 of the 

 catalogue cited above, which shows that in the form of its variations 

 this star closely resembles y] Aquilce and h Cephei. Another reason for 

 excluding W Virginis and the last four stars of the list is, that their 

 light is variable at their maxima, and in four of the five cases at their 

 minima. This frequently happens with stars of Class II., but would 

 not be readily explained in stars of Class IV. 



The Uranometria Argentina adds U Monocerotis to the list of red 

 stars. All stars whose period lies between 32 and 72 days have, 

 therefore, been called red, except R Coronce Australis. This star is so 

 faint that its color might well have been overlooked. 



A further discussion would have been made of T Monocerotis, but 

 no means exist for converting into light ratios the scale of magnitudes 

 of its light curve. As the brightness of the comparison stars are not 

 given, we have no means of knowing whether a tenth of a magnitude 

 corresponds to the same light ratio when this star is faint, as when it is 

 briglit. A preliminary trial showed that the maximum appeared to 

 occur more suddenly, and the minimum more slowly, tlian theory 

 would indicate. The large range of variation of this star renders it 

 well suited for study, and the same may be said of some others of the 

 list, as a slight increase in the difference between the maximum and 

 minimum greatly increases the severity of the test the liglit curve 

 offers to theory. 



The system which appears to govern the position of the companions 

 to these stars suggests an investigation which might lead to important 

 results. The planes of the orbits of the binary stars are defined by 

 their inclination and the position angle of the node. Since we cannot 

 determine micrometrically the direction in which the orbit is inclined, 

 we can only say that the pole of this orbit lies in one of two places. 

 Should any law be discovered, we might then decide for any particular 

 siar what sign should be given to the inclination, and also whether the 



