6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



For diameter 3.66 cm. and fj'=^y.o^ cm., 



(1.8^)2 



Note. — In certain experiments on the hand (see Table A) a smaller open- 

 ing was used having diameter 2.42 cm. For this, sin^ d = .02877. 



The paper referred to above (Smithsonian Misc. Coll., Vol. 72, 

 No. 13) gives the constant of melikeron No. i as 2.45. That is, by 

 multiplying 2.45 by the square of the current, in amperes, required to 

 compensate, we obtain, in calories per sq. cm. per minute, the differ- 

 ence in radiation between the shutter and whatever object is exposed 

 on removing the shutter. The difference in radiation between the 

 " i)in-cushion " shutter and the skin would be 



A shunted voltmeter of 49.3 ohms resistance was used to measure 

 the current, hence 



2.45 V^ _ .g oioqSF^ 

 (49-3)^ sin^^ " s'm^ 

 where [^' = voltmeter reading in volts. 



The shutter being a black body at temperature to C., radiates 



8.20+10-1^(273 + /,,)* 



Then the skin radiates 



8.20 X 10-" (273 + to)* + .001008 gjj^ 



if we neglect the radiation which appears to arise in the skin, but 

 really is reflected by the skin into the instrument and was emitted by 

 the walls of the room, the vestibule of the melikeron, and so forth. 

 If the skin was a perfect radiator or " black body " this reflection 

 correction would be zero. 



We may get a line on this by computing the temperature of the 

 skin, assuming it " black " and comparing with observed tempera- 

 tures taken directly. 



If Ti = absolute temperature of skin 



To = absolute temperature of pin-cushion shutter, 



Skin radiation =:orTi* 

 Shutter radiation ~ aTo* 



Then i?=. 001 008 ~J^ =a(T,'-To^) 

 sui- 6 ^ ^ 



T,' = To' + .001008^^^ =To'+ 1.939V' X 10' 



