XXI. Researches in circular solar spectra, applied to test residuary aberration in microscopes and telescopes, and the construction of a compensating eyepiece, being a sequel to the paper on a searcher for aplanatic images

The researches detailed in the present paper were commenced in May 1871. The results arrived at were largely obtained from using the microscope. Similar but less brilliant and more scanty appearances can be obtained with the telescope; but the very high power and ready adaptability of the former confers some advantages not offered by the latter. In both, however, the same principles are illustrated. A cone of rays of small angular aperture having the object-glass for its base in each case engages the eyepiece and emerges parallel, and the eyepieces are similar in each.