An examination of the earth metals contained in samarskite proved that the rare earth-metal announced by Delafontaine under the name of “philippium” was a mixture of yttrium and terbium.[24] The spark spectrum of terbium was at the same time mapped by him and Schuster. An examination of a specimen of oxide which ought to contain “philippium” in large quantities if that chemical element existed showed no conclusive evidence of any other metals than yttrium or terbium.[25] In 1882 he sent to the French Academy a note on a re-determination of the atomic weight of carbon by the method of Dumas and Stas, using Cape diamonds, and obtained the value 12·002 (O = 16) as the mean of six experiments (_Chem. Soc. Abstracts_, 1882, 724). He also showed, with the assistance of Schuster, that the spectrum of the carbon dioxide furnished by the South African diamond was identical with that furnished by other forms of carbon. So long as he remained in Manchester Roscoe was in the habit of making occasional contributions to the meetings of the Literary and Philosophical Society on general or local interest. Among these communications were papers on arsenic-eating in Styria; on a crystallizable carbon compound in the Alais meteorite; on the amount of carbonic acid in Manchester air; on the corrosion of leaden hot-water cisterns; Dalton’s first table of Atomic Weights, etc.—all of which are printed in the _Proceedings_ or _Memoirs_ of the Society. Roscoe was largely instrumental in making spectrum analysis first known to British men of science and the British public generally. Almost immediately after the publication of Bunsen and Kirchhoff’s classical paper in _Poggendorff’s Annalen_, he translated it for the _Philosophical Magazine_. He also gave many public lectures on the subject, beginning with that at the Royal Institution on March 1, 1861—one of the most successful of the many he delivered there. Indeed, there were few of our larger towns in which he was not invited at one time or other during the sixties and early seventies to lecture on that astonishing development of nineteenth-century science. These lectures involved no inconsiderable effort. They necessitated much bulky and fragile apparatus difficult to transport. Some of the illustrations could only be shown to a large audience by means of the electric lantern, and this, in those days, needed the provision of a large battery of Groves’s cells; electricity “laid-on” by a public authority was not then, as now, almost everywhere available.