TY  - RPRT
TI  - Letter Circular 515: selenium cells; photocells; thermopiles (supersedes Letter Circular 199)
PY  - 1938
PB  - National Institute of Standards and Technology
CY  - Gaithersburg, MD
SN  - LCIRC 515r1938
DO  - 10.6028/NBS.LCIRC.515r1938
ER  -