Westland. — Southern Variable Stars. 



501 



plate on it on the 25th November, and on examining the result afterwards 

 I found the variable rather bright. It was really about the sixth magni- 

 tude at the time, and, as the exposure had been long enough to show ninth- 

 magnitude stars, a star of sixth magnitude left a very distinct impression. 

 I watched the star for several weeks, and saw it pass through a maximum 

 in January, 1912. 



This star follows a custom which is common among variable stars, in 

 that it rises to maximum very rapidly, but falls slowly. The usual method 



^W v4/ ' -^'^ Q^ ^-^ /'^^ /'■^ du^ "?<* ^'^- -^ ^"~ 



V /o io 3a f 'f ' II Zi 3i /o 2o 3o it, la Jo 9 /J? 2f f /f if S ,g ig J ij s.y ^ ij i^ / //.?/ / //V . 



vf_a^ 1 1 1 1 T 1 r ■ ! 1 1 1 1 1 1 1 1 1 ! 1 ' r T 1 1 1 1 1 1 1 1 1 1 1 1 — -r 



40 

 so 



u 



;.. 

 8o 



Fig. 1.— Curve of R. Hydrae in 1913. 



of dealing with observations is to plot them on squared paper, making the 

 horizontal scale represent time and the vertical scale show the magnitudes. 

 Then the characteristic I have mentioned is expressed by saying that the 

 rise is much steeper than the fall. The curve of this star in 1913 is shown 



in fig. 1. 



^^ 



^ 



6a 



$0 



Q/or ^W i^ fJ^ ^^ A^' 



// II 31 /o Ho 3o /o Zo 3o f /f if ^ If 2^ g /? iS 7 



Fig. 2. — Curve of T. Centauri in 1913. 



A peculiarity in the period of R. Hydrae is that it is growing decidedly 

 shorter. The observations of last year show that only 409 days elapse 

 between one maximum and the next, whereas all books of reference at pre- 

 sent give the period as 425 days. Mr. Gore's book states that the period was 

 500 days in the year 1708, 487 days in 1785, 461 in 1857, and 437 in 1870. 



There are a good many variables whose curves are similar to that of 

 R. Hydrae. A few of these curves — Mira Ceti, R. Leonis, and others — are 

 given herewith.* Fig. 2 is the curve of a southern star, T. Centauri, 



* Other diagrams and lantern -slides were shown at the meeting. 



