Meteor Observing.—The actual observation of meteors forms one of the branches of astronomy best suited to amateurs. The only equipment needed is a star chart on which to plot the paths, a notebook and watch. Observations are made by noting care fully the points among the stars at which the meteor begins and ends, and plotting this path upon the map. Records of the time, colour, magnitude, etc., are made in the notebook at the same time. Societies for this work, largely composed of amateurs, now exist in several countries. Such work is of real scientific value and is the basis for advances in meteoric astronomy.
For more than 3o years attempts have been made to apply pho tography, but progress has been slow. It has been proved, how ever, that only short-focus instruments of considerable light gathering power are of real service. Lenses four to six inches in diameter with a focal ratio of about :4 have been most used. Even with these only bright or very slow-moving meteors regis ter themselves, and as no great shower has come of late the total number of trains photographed has not exceeded a few hundred. In some cases enough have been photographed on one night to give a radiant, but most are isolated. Attempts to obtain heights and velocities by photography have met with some success, but progress has been painfully slow. Nevertheless this method holds out great promise for the future. Some of the few radiants so
derived were found with gratifying exactness.
Accepting the Planetesimal Hypothesis, or some modification of it, as the true one, we may look upon all meteoric bodies as the debris of evolution—as fragments left over, or as parts of plane tesimals that were destroyed before achieving full growth. But a study of the orbits and velocities of numerous fireballs and me teorites proves that they originated outside the Solar System. Analyses of some such meteorites prove beyond controversy that they once formed part of larger solid bodies of planetary dimen sions. Hence we must infer an origin for these similar to those we know originated here. This brings us to one of the most important results of recent meteoric astronomy : if a catastrophic origin must be assumed for our Solar System, similar origins must be assumed for innumerable others, and hence we must admit that many other stars have systems of planets which were evolved in a manner similar to our own.