deserved, and they only became an object of especial interest to students of physics when they were again studied by the famous German optician Fraunhofer, a generation later.
Incidentally the experiments are of interest, as yielding us a measure of the excellence of Herschel's telescopes, and a measure which is quite independent of the keenness of his vision. From them we may be sure that the efficiency of the nine-inch mirror used was not sensibly less than that of the highest theoretically attainable excellence. In this connection, too, we may refer to the Philosophical Transactions for 1790, pp. 468 and 475, where Herschel gives observations of both Enceladus and Mimas seen in contact with the ball of Saturn. I have never seen so good definition, telescopic and atmospheric, as he must have had on these occasions.
Researches on the Spectra of the Fixed Stars.
The spectroscope was applied by Secchi to the study of the spectra of the fixed stars
