THERE are numerous gaps in our knowledge of the physics and chemistry of colored glasses which either have not been spanned at all or have been flimsily bridged by theory supported more or less by inadequate experimental data. On the other hand, a number of investigators have made excellent contributions which indicate that light may be shed on some of the questions by physical data of various kinds. Hyde, Cady, and Forsythe, in studying red pyrometer glasses, noted the influence of temperature

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... on the transmission characteristic of a red glass and investigated this influence for temperatures of 20' C. and 80" C. The transmission-factor of the red glass is a,ppreciably less for various wave-lengths a,t the higher temperature than at 'the lower temperature. It appeared of interest to study this aspect with a number of commercial colored glasses and later to carry the work further with glasses especially made for the purpose. Only the transmission-factor for t'otal visible radiatioa has been considered so far, but an idea of the change in spectral transmission may be gained by noting lthe change in cslor of the heated specimen. A given specimen was cut into two pieces and one was kept at room temperature, while the t'emperature of the other was increased gradually to 350" C. The relative transmission-factors of the two specimens were measured throughout this range, and a few of the results are presented in the table. No color-difference was encountered during the measurements except that due to a change in the spectral transmission characteristic of the heated specimen. This color-difference became very marked for specimens 5 and IO at temperatures above 100' C. No analyses of the glasses have been made in this preliminary work. The color of the hot specimen is given as compared with that of the cold * Communicated by the Director. 22.5