386 



PROCEEDINGS OF THE AMERICAN ACADEMY 



decreasing and while increasing. The successive columns give the 

 light in magnitudes, the corresponding times before and after the min- 

 imum, and the mean of these times. 



TABLE VIIL — Time of Minimum. 



From the numbers in the last columns we may infer a correction of 

 13 minutes when the light equals 1.24, or at the minimum. In other 

 words, thirteen minutes should be subtracted from the adopted epheraeris 

 of the minima. The minimum can evidently be determined with much 

 precision from any observations of the times at which the light is equal 

 when diminishing and increasing. If the light is less than 2.9, or the 

 interval between the times less than five hours and a half, it is only 

 necessary to take the mean of the two times and subtract from two to 

 four minutes. The exact correction is found from the last column of 

 the table after subtracting thirteen minutes. The observation is easily 

 made witli a small telescope, as there are so many comparison stars of 

 suitable briglitness near the vari:il)le. Doubtless a very precise de 

 termination of the minimum could thus be easily obtained. 



To reduce the separate observations we must determine the rate of 

 change in light. The method employed for ft Persei has again been 

 used; the results are given in Table IX. The colunnis have the same 

 meaninnf as in Table III. 



