[Sidenote: GLASS-MAKING LAID ASIDE.] In answer to this Faraday sent the following letter to Dr. Roget, Sec. R.S.:-- [_M. Faraday to P. M. Roget._] Royal Institution, July 4, 1831. DEAR SIR,--I send you herewith four large and two small manuscript volumes relating to optical glass, and comprising the journal book and sub-committee book, since the period that experimental investigations commenced at the Royal Institution. With reference to the request which the Council of the Royal Society have done me the honour of making--namely, that I should continue the investigation--I should, under circumstances of perfect freedom, assent to it at once; but obliged as I have been to devote the whole of my spare time to the experiments already described, and consequently to resign the pursuit of such philosophical inquiries as suggested themselves to my own mind, I would wish, under the present circumstances, to lay the glass aside for a while, that I may enjoy the pleasure of working out my own thoughts on other subjects. If at a future time the investigation should be renewed, I must beg it to be clearly understood I cannot promise full success should I resume it: all that industry and my abilities can effect shall be done; but to perfect a manufacture, not being a manufacturer, is what I am not bold enough to promise. I am, &c., M. FARADAY. The optical glass was a failure, so far as concerned the original hope that it would lead to great improvements in telescopes. Nevertheless it furnished scientific men with a new material, the “heavy glass” consisting essentially of boro-silicate of lead, for which sundry uses in spectroscopy and other optical instruments have since been found. In 1845 Faraday added this note:-- I consider our results as negative, except as regards any good that may have resulted from my heavy glass in the hands of Amici (who applied it to microscopes) and in my late experiments on light. These were the famous experiments on magneto-optics and diamagnetism. Incidentally the research had led also to the permanent engagement of Sergeant Anderson as assistant to Faraday. [Sidenote: RESEARCHES AND LECTURES.]