From this time forward Brewster seems to have manifested the keenest interest in all questions connected with the origin and history of a substance possessing such singular physical properties. By the aid of Mr. Swinton, secretary to the government at Calcutta, he formed a large and interesting collection of all the different varieties of tabasheer from various parts of India. He also obtained specimens of the bamboo with the tabasheer _in situ_. In 1828 he published an interesting paper on "The Natural History and Properties of Tabasheer" (_Edinburgh Journal of Science_, vol. viii., 1828, p. 288), in which he discussed many of the important problems connected with the origin of the substance. From his inquiries and observations, Brewster was led to conclude that tabasheer was only produced in those joints of bamboos which are in an injured, unhealthy, or malformed condition, and that the siliceous fluid only finds its way into the hollow spaces between the joints of the stem when the membrane lining the cavities is destroyed or rent by disease. Prof. Edward Turner, of the University of London, undertook an analysis of tabasheer, the specimens being supplied from Brewster's collection (_Edinburgh Journal of Science_, vol. viii., 1828, p. 335). His determinations of the specific gravities of different varieties were as follows: Chalky tabasheer. 2.189 Translucent tabasheer. 2.167 Transparent tabasheer. 2.160 All the varieties lose air and hygroscopic water at 100° C., and a larger quantity of water and organic matter (indicated by faint smoke and an empyreumatic odor) at a red heat. The results obtained were as follows: Loss at 100° C. Loss at red heat. Chalky tabasheer. 0.838 per cent. 1.277 per cent. Translucent tabasheer. 1.620 " " 3.840 " " Transparent tabasheer. 2.411 " " 4.518 " " Dr. Turner found the ignited Indian tabasheer to consist almost entirely of pure silica with a minute quantity of lime and vegetable matter. He failed to find any trace of alkalies in it. In 1855, Guibourt (_Journ. de Pharm_. [3], xxvii., 81, 161, 252; _Phil. Mag_, [4], x., 229) analyzed a specimen of tabasheer having a specific gravity of 2.148. It gave the following result: Silica. = 96.94 Potash and lime. = 0.13 Water. = 2.93 Organic matter. = trace