III. ABSORPTION OF VARIOUS SPECIMENS AT HIGH TEMPERATURE. T HE effect of high temperature on the absorption of the specimens described in this paper is a continuation of the work done on uranium glass at high temperatures 1 and at low temperatures. 2 The substances investigated consisted of various colored glasses of unknown composition, a few cubes, the composition of which was partially known, and a cube of fluorite. Only a few of these specimens showed any fluorescence. APPARATUS. The

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... n G was placed inside a hollow iron cylinder, as indicated in Fig. 16 . On the outside of the cylinder was wound a few layers of iron wire and heating was secured by sending an electric current through this wire. The temperature of the specimen was measured by an iron constantan thermo-j unction /. For convenience in inserting the specimen into the furnace, it was first placed inside of a cylindrical iron case C. This case fitted rather closely into the opening in the iron cylinder and was pushed into place by another hallow iron tube T, the inner cross section of which was slightly smaller than that of the case. In order to prevent internal reflection as much as possible, iron washers W\ and W2 were placed at each end of the iron case. To prevent air currents and therefore unequal heating, two mica windows were placed in positions indicated by Mi and M%. A hole was drilled in the side of the furnace for the purpose of observing the effect of high temperature on the fluorescence of the specimens studied and was filled with a plug P when the intensity of transmitted light was