254 THE HUMAN MOTOR 



than 18% of volatile matters and those which contain 19% to 

 30% ; the latter explode violently, the more so if the grains are 

 small. 



The combustibility of dust is due to the fact that the individual 

 grains have a big surface in proportion to their mass. Chauffeurs 

 have been known to have eye troubles,, due to the fact that the 

 dust of the roads contains particles of tar. In fact, whilst 

 ordinary dust (silica or calcium) only cause a slight inflammation 

 of the eyelids, tar dust cause a more serious conjunctivitis of 

 a purulent character^ 1 ) The same occurs with workmen who 

 work certain coals, because of the bituminous dust.( 2 ) Apparatus 

 for sucking up the dust by means of compressed air has already 

 been installed in coal mines. One such apparatus working 20 

 days a month is sufficient for the clearing of galleries of a total 

 length of 1,600 metres. ( 3 ) 



Exhaust fans are used to get rid of the dust in cotton mills, 

 which would injuriously affect the workpeople. In this way the 

 frames of the machinery can be properly cleaned without inter- 

 rupting work.( 4 ) 



187. The Influence of Radiation. Solar Action. Radiation is 



of many kinds. Calorific radiation has been studied in connection 

 with temperature ( 165). It is most intense at the red end of 

 the spectrum. Radiant heat is almost entirely arrested by 

 glass. The heat which is experienced in a green house, or in any 

 environment bounded by panes of glass is not caused by the 

 opacity of the latter; in fact, there is the same elevation of tem- 

 perature behind slabs of rock salt, which is most transparent to 

 heat (diathermic). Wood has shown that the enclosed air is 

 heated because it does not circulate. ( 5 ) 



Calorific radiation is present in all sources of light, beginning 

 with the sun. A calorific radiation of 0-0036 c. per square centimetre 

 per hour produces a sensation of heat whilst, if it were 6-5 

 times more intense, say -024 c., it would be intolerable. An 

 ideal source of light should not radiate more than 0-0021 c., 

 according to Rubner.( 6 ) In comparing the various methods of 

 lighting, one finds that all, except lighting with kerosine oil, 

 satisfy this condition. ( 7 ) 



The luminous part of the spectrum, or, more exactly, the whole 

 light produces various effects on the organism, some of which 



(^ True et Fleig (Comptes Rendus Acad. Sc., Sept., 1910). 



( a ) Congrls des Maladies Professionnelles de Bruxelles, Sept., 1910 



( 3 ) Genie civil, 19th Aug., 1911, p. 337. 



() Genie civil, 12th April, 1911, p. 319. 



(*) Wood (Phil. Magazine, 1st Sept., 1909, p. 319). 



(') Rubner (Arch. f. Hygiene, 1895, vol. xxiv., p. 193). 



( 7 ) V. Woege (Journal fur Gasbeulechtung, 1911, No. 13). 



