The Collaborative International Dictionary of English v.0.48:

Radiometry \Ra`di*om"e*try\ (r[=a]`d[i^]*[o^]m"[-e]*tr[y^]), n.
   (Physics)
   The use of the radiometer, or the measurement of radiation.
   -- Ra`di*o*met"ric (r[=a]`d[i^]*[-o]*m[e^]t"r[i^]k), a.
   [Webster 1913 Suppl.]