Page:Popular Science Monthly Volume 69.djvu/181

Rh were obtained which showed well the characteristics of scores of spectra on a single plate. Variable stars of long period were found to have spectra in which the hydrogen lines were bright, when the variables were near maximum. By taking advantage of this spectral peculiarity Mrs. Fleming has been able to 'pick up' as a by-product of other investigations concerning stellar spectra, some 200 variables of long period.

In 1895, the writer, while engaged in photographic work at the Arequipa Station of the Harvard Observatory, began an examination of photographs of the globular clusters of stars. By the use of improved devices for controlling the motion of the telescope, satisfactory photographs were obtained of the dense globular clusters. An examination

of these led to striking results. It was found that while certain clusters contained few or no variable stars, other similar clusters were closely packed with them. Messier 3, a faint group, barely visible as a hazy star to the naked eye, was found to contain 137 variables out of 900 stars examined, or about one in every seven stars. This is by far the greatest proportion of variables yet found anywhere in the sky. Over 500 variable stars have been found so far in dense globular clusters, and, undoubtedly, these do not entirely exhaust the number.

Madame L. Ceraski, wife of the director of the astronomical observatory of Moscow, has found a large number of variables by an examination of photographs made by M. Blajko, of the same