Physical Problems in Study of Conditions for Health 31 



for open air conditions. The determination of corrections for 

 incident radiation, and surface emissivity constitutes one of the 

 chief difficulties in the work. 



A radical simplification in the design and operation of these 

 instruments is also essential before they can pass into the general 

 usage which they deserve on theoretical grounds. An instrument 

 which virtually requires the performance of an experiment in order 

 to obtain a reading, or which requires skilled attention, is very 

 difficult to introduce into customary usage. Readings must be 

 available instantly on a scale or dial, and the expense must not be 

 prohibitive. Although this particular field of work as a whole 

 is difficult both theoretically and experimentally, there are many 

 pieces of information that are worth securing and which should 

 require little more than a kata-thermometer, a pitot-tube, an 

 electric fan, an electric heater, an aspiration hygrometer and the 

 facilities for enclosing the instrument in vacuo. 



(6) Devices which when desired can be made to insure a more 

 definite avoidance both of ''monotonous'' conditions, and of ''monot- 

 onous'' variations in the large calorimeters used for metabolism 

 experiments, are required in conjunction with the means of knowiug 

 exactly what conditions are being produced. At present the 

 results of the best investigations are somewhat in disagreement, 

 very largely on account of uncertainty about this matter. 



(7) The theory of the atmometer and its relation to the cooling 

 and evaporative power of the surrounding atmosphere on other 

 surfaces, requires considerable amplification with reference to the 

 points which have been indicated in regard to hygroscopic surfaces. 



(8) The influence of the atmospheric conditions on the electrical 

 state of surfaces and small particles, requires more attention. 

 The circulation of dust particles is very greatly influenced by the 

 electrical charges which they obtain in dry moving air. The 

 critical conditions which lead to extreme static charging of surfaces, 

 are not completely understood, and in many manufacturing pro- 

 cesses are a source of danger. Very little attention has been paid to 

 the possible reaction of the surface electrical conditions which are 

 created in turbulent arid atmospheres on the subcutaneous nerve 

 endings. Ionization experiments alone will not suffice in dealing 

 with such problems; questions of surface electrical conductivity 

 arise and lead one at once into the large field of problems which 



nvolves the simultaneous consideration of the surface electrical 

 conductivity, the concentrations of conducting medium, and the 

 surrounding conditions. 



