V. On the spectra of some of the nebulæ.—On the spectra of some of the fixed stars

The author commences by showing the importance of bringing analysis by the prism to bear upon the remarkable class of bodies known as nebulæ, especially since the results obtained by the largest telescopes hitherto constructed appear to show that increase of optical power alone would probably fail to determine the question whether all the nebulæ are clusters of stars too remote to be separately visible. The little indication of resolvability, the absence of central condensation, the greenish-blue colour, and the intrinsic brightness characterizing many of the nebulæ classed by Sir W. Herschel as planetary, induced the author to select chiefly nebulæ of this class for prismatic observation.