Example I.—A black body at an absolute temperature T1 is found to give twice the intensity observed at 1200° abs., the comparison being made with red glass transmitting wave-length 65 × 10-6 cms. To find the value of T1.
Applying values to formula (3)
log 2 = ( 1450000 ⁄ 65 ) log 2·7183 × ( 1 ⁄ 1200 - 1 ⁄ T1 )
and
0·3010 = ( 1450000 × 0·4343 ⁄ 65 ) × ( 1 ⁄ 1200 - T1 ⁄ 1 )
from which T1 = 1237° abs.
Example II.—The intensity of the radiations from a black body at 2000° abs. are found to be equal to those from a given standard, taken as unity. To find the intensity at 3000 abs., compared with the same standard. λ = 65 × 10-6 cms.
Applying in (3) as before,
log ( J1 ⁄ 1 ) = ( 1450000 × 0·43435 ⁄ 65 ) × ( 1 ⁄ 2000 - 1 ⁄ 3000 )
from which log J1 = 1·615, and J1 = 14·5.