Note FO — Chapter VII · THE SENSES OF ANIMALS. (continued 2)
Reading edition
Professor Langley finds that the maximum effect with a radiating
source at 170° C. is at about5.0thousandths of a millimetre wave-length.
"100° C."" 7.5 """
"0° C."" 11.0 """
We are sensitive to radiations from a body at 100° C. But when the temperature falls below the normal temperature of the body we are not sensitive to heat-vibrations, but to loss of heat from the surface exposed. The limit of sensibility to heat-vibrations, therefore, probably lies between 7.5 and 11 thousandths of a millimetre. I have taken about 9.25 as the limit.