lO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



TRANSMISSION OF RADIATION THROUGH THE SKIN 



In measurements previously made comparing temperatures by the 

 thermoelement device with temperatures computed from melikeron 

 radiation measurements, it was noted (see Smithsonian Misc. Coll., 

 vol. 81, no. 6, p. 19) that in measurements on the uncovered skin the 

 computed temperatures were about i° C. higher than those measured 

 by the thermoelement. In measurements on clothing and calorimeter 

 this difference appeared to be much smaller. It was thought that pos- 

 sibly the skin was sufficiently transparent to long-wave radiation so 

 that the melikeron in reality received radiation from a warmer layer 

 below the outer surface. To test the transparency of the skin the 

 following arrangement was prepared : 



Pyranometer S. I. 8 (for description and use of pyranometer see 

 Smithsonian Misc. Coll., vol. 66, nos. 7 and 11) was mounted without 

 glass hemisphere and with the absorbing strip vertical. A grid, cut 

 from platinum foil and blackened, served as a source of low tempera- 

 ture radiation. The resistance of the grid at room temperature 

 (22.5° C.) was 2.68 ohms. A voltmeter measured the potential fall 

 across the grid, and an ammeter measured the current flowing. The 

 temperature of the grid was roughly determined .from its increase in 

 resistance as computed from the voltmeter and ammeter readings. A 

 doublewalled screen close to the grid exposed 8 sq. cm. of grid sur- 

 face. The distance from grid to pyranometer was 10 cm., which per- 

 mitted the interposition of two filters and a double-walled shutter. 



The accepted procedure with the pyranometer is to use the first 

 swing of the galvanometer as proportional to the incident radiation. 

 When the shutter is opened, exposing radiation to the pyranometer 

 strip, the galvanometer spot immediately starts to move and, if the 

 radiation remains constant, swings to its maximum deflection in a 

 definite time. In the galvanometer used (Leeds and Northrup Type 

 R) this first swing required 3.53 seconds (mean of many trials). It 

 was noticed that when certain more or less opaque filters were inter- 

 posed the galvanometer spot did not start to move immediately and 

 took appreciably longer than 3.5 seconds to reach maximum deflection. 

 This delayed deflection was due to a combination of the direct radia- 

 tion transmitted by the filter and of the radiation from the filter 

 itself due to its increased temperature when exposed to the grid. To 

 minimize this indirect heating effect, a stop watch was used and only 

 those readings retained in which the maximum deflection was reached 

 within -J second of 3.5 seconds. Temperatures of the grid source 

 were varied in the range 75° to 170° C. 



