Page:Popular Science Monthly Volume 18.djvu/199

Rh found the shower double at 46° $$+$$ 57.6° and 38° $$+$$ 56°; and in 1880 he strongly corroborated the results obtained at Bristol, though his observations were mainly confined to the night of August 9th. At the latter station the radiant apparently advanced among the stars of Perseus, for, while early in the month it was observed at 38° $$+$$ 56°, it had shifted to 49½° $$+$$ 57½° by the 13th. The same peculiarity was noted in 1877, when the following determinations were made:

There is a prominent display of meteors from the star-group χ Persei at the end of July and beginning of August, and it is possible that these showers may belong to the same system of concentric meteor streams. It is certain that this fact of a progressive radiant requires fuller elucidation, and to this end observers should keep the data obtained each night separate. It may also be suggested that the radiant point should be ascertained during each hour of observation, and then, when the series are compared, any displacement must immediately become obvious, and its extent and character well defined by the observations. The meteors from Perseus are so numerous, and the place of divergence so readily denoted by their enduring streaks, that there will be no difiiculty in an investigation of this kind. The last two years' observations have shown how exactly the radiant may be found by carefully conducted researches, and how closely the positions derived by different observers will agree on being compared together:

From these values a mean of 44.8° $$+$$ 56.8° is derived, which is probably very near the truth. There is a secondary shower higher in declination (at about 44½° $$+$$ 60°), but this is merely a branch of the same stream, for the meteors exhibit the same specialties of appearance as those common to the major shower. An apparent diffuseness of the radiant point is often brought about by imperfectly registered tracks, and by allotting the meteors of bordering showers to the radiant of the Perseids, when in fact they belong to evidently distinct families.

A few years ago the writer undertook the investigation of these co-Perseid showers from the large mass of shooting-stars which had been registered at this epoch at foreign observatories, and are contained