are cub. in. and cub. in. respectively, and .
Also, if
(5) The reading of a Féry’s Radiation pyrometer is related to the Centigrade temperature of the observed body by the relation
,
where is the reading corresponding to a known temperature of the observed body.
Compare the sensitiveness of the pyrometer at temperatures C., C., C., given that it read when the temperature was C.
The sensitiveness is the rate of variation of the reading with the temperature, that is . The formula may be written
,
and we have
.
When , and , we get , and respectively.
The sensitiveness is approximately doubled from to , and becomes three-quarters as great again up to .