TY  - RPRT
TI  - Letter Circular 673: optical instruments, refractometry and optical properties of glass (supersedes Letter Circular 571)
PY  - 1941
PB  - National Institute of Standards and Technology
CY  - Gaithersburg, MD
SN  - LCIRC 673
DO  - 10.6028/NBS.LCIRC.673
ER  -