REPORT OF THE SECRETARY 113 



error, and a certain slowness of reading characteristic of the silver- 

 disk instrument which it is hoped to improve upon. Thus far the 

 new instrument, of a compensating electrical type, has not quite 

 reached expectations, but it is still hoped to overcome its deficiencies 

 and retain its advantages. 



Attention was also paid to the improvement of the radiometer for 

 measuring the energy of the spectra of the stars. In this instrument 

 it was proposed to seal the sensitive ejement in a truly circular, 

 optically figured quartz tube containing a small pressure of hydrogen, 

 and to adjust the position and direction of the system by moving and 

 rotating the inclosing cylinder. The device was made ready for use 

 by the writer during the summer of 1928 at Mount Wilson, Calif., 

 with good results, which will properly be described in next year's 

 report. 



In connection with a research by Mr. Aldrich on the radiation and 

 convection of the normally clothed human body, a number of instru- 

 mental appliances were also made. 



(c) Research on the loss of heat from the human hody. — Inquiry 

 was made of the writer by Mr. T. J. DufReld, secretary to the New 

 York Commission on Ventilation, as to the proportion of the loss of 

 heat of the normally clothed human body which should be ascribed 

 to radiation rather than to convection by the air. The subject needed 

 investigation, and at the writer's suggestion a grant of $1,000 was 

 made by the New York Commission on Ventilation to the Smithsonian 

 to promote it. My colleague, Mr. Aldrich, undertook the work and 

 made several long series of novel and valuable experiments, the results 

 of which will shortly be published. He employed principally two 

 instruments: First, the melikeron, or honeycomb pyranometer, for 

 observing radiation of bodies at low temperature, first described in 

 these reports for the years 1919 and 1920; and second, a special 

 thermoelectric temperature tester constructed for the research. 



Mr. Aldrich sums up his results as follows : 



(1) The radiation from the skin and clothing is approximately 

 that of a " black body " or perfect radiator. 



(2) Skin temperatures computed from melikeron radiation measure- 

 ments are about 1° C. higher than skin temperatures measured di- 

 rectly with the thermoelement. This is not true on clothing of 

 calorimeters. Apparently the melikeron sees deeper into the pores 

 of the skin than the level observed by the thermoelement. 



(3) A cloth-covered, vertical, cylindrical calorimeter at body tem- 

 perature loses in still air 60 per cent by radiation, 40 per cent by 

 convection. A similar horizontal calorimeter loses 54 per cent by 

 radiation, 46 per cent by convection. The human body convection 

 loss is probably similar to this; that is, the convection loss is roughly 



