came in the first years of this century, with the discovery of three small planets having orbits lying between those of Mars and Jupiter. Herschel gave the name Asteroids to these bodies. As the appropriateness of this term had been violently assailed, the discovery of Juno, in 1804, the third one of the group, led to a careful experimental study of the defining power of the telescope used, and of the laws governing the phenomena of spurious disks.
With a telescope of about nine inches in aperture, Herschel found that if Juno subtended an angle greater than a quarter of a second of arc, a certain indication of the fact would have shown itself in the course of the experiments. This conclusion was a justification of the name Asteroid, since the appearance of the new planet was strictly stellar. On other grounds, a better name might have been selected.
In the paper giving the results of the experiments, the phenomena of the spurious disks are very completely described; but they did not attract the attention which they
