Scientific paper issued by the Bureau of Standards over thermal expansion of fused silica. As stated in the abstract, "this paper gives the results of an investigation on the thermal expansion of transparent and nontransparent fused silica for various temperature ranges between -125 and +1,000 degrees Celsius. A detailed description of the apparatus and the methods used in this research and a summary of available data obtained by previous observers on the thermal expansion of fused silica are given" (p. 1). This paper includes tables, photographs, and illustrations.