12 
HAGEN. 
character of the light-curve is, like that of U Geminorum, the 
inversion of the Algol-type, the maximum brilliancy flash¬ 
ing up suddenly and lasting but a short time. This uni¬ 
formity in period, range, and light-curve is peculiar to the 
cluster Messier 5, and has not been observed in other clus¬ 
ters, as, for instance, in a> Centauri, in which over a hundred 
variables of very different characters have been found. 
The uniformity in the effect calls for a uniform cause, and 
if the writer be allowed to make a suggestion of his own, he 
would like to offer the following: The mean range of 1.1 
magnitude multiplied by Pogson’s light factor, 0.4, shows 
that these 38 variable stars lose about one-half of their light 
at the time of their minimum brightness. This would hap¬ 
pen, if each of them w^ere a binary star, with components of 
equal brightness and with orbits whose planes pass through 
our solar system. If this explanation expressed the physical 
cause of this phenomenon, it would throw some light on the 
interior structure of this cluster. 
2. Spectroscopic Binaries .—When the past generation of as¬ 
tronomers opened the new field of stellar spectroscopy their 
studies were mainly directed to the physical aspect and clas¬ 
sification of the stellar spectra, while the measuring of the 
spectral lines was reserved to our present generation. The 
former study shows its progress in the number of stars ex¬ 
amined, in the method of the objective prism, in the addi¬ 
tion of a fifth type to Secchi’s historical types, and in sub¬ 
dividing these types. This progress is largely embodied in 
the volumes published by Director Pickering, but does not 
form the special subject of this report. Nor can the shifting 
and doubling of some spectral lines be put under the head 
of “ recent progress ” in astrophysics. What calls for our 
attention here is the periodicity in the shifting and doubling 
of these lines. 
In addition to our scanty knowledge in this field, we have 
two recent discoveries, one by Mr. Campbell regarding the 
pole star, the other by Mrs. Fleming about the star C Cen¬ 
tauri. The velocity of Polaris in the line of sight has been 
