CHAPTER VIII 



PRESSURE AND RADIATION 



Preliminary — Increased pressure — Diminished pressure — Radiation — 

 Electricity — References. 



PRELIMINARY. 



The present chapter is devoted to the study of the pathological 

 effects of atmospheric pressure when considerably increased or 

 diminished, and of the rays from the sun under conditions which 

 produce disease. 



If there are pathological effects, other than those already 

 mentioned (p. 88), as the result of rays from the moon, they are 

 unknown. Probably they do not exist, and possibly the effects 

 already described may be due to the fact that the moon's rays when 

 reflected become polarized. 



A passing reference will be made to the effects of lightning, as 

 death from this cause is not infrequent in the tropics. 



INCREASED PRESSURE. 



The work of facilitating trade by means of roads and railways 

 throughout the tropics necessitates the construction of bridges 

 across deep rivers, and therefore for many years to come the effects 

 of artificially increased atmospheric pressure will be more obvious 

 in these regions than elsewhere. 



Moreover, for centuries tropical natives have been exposed to 

 increased pressure when diving for commercial purposes, and though 

 generally they do not remain down long enough to suffer any bad 

 effects, still at times these are noted. 



The effects of greatly increased atmospheric pressure are usually 

 termed ' caisson disease,' because it was observed first in connection 

 with the special compressed air apparatus used by engineers for 

 ' work under water. 



In 1878 Paul Bert, as the results of his experiments upon animals, 

 showed that the extraordinary symptoms of this disease could all 

 be explained by increased atmospheric pressure, but it is mainly 

 by the labours of Leonard Hill that Paul Bert's work has been 

 confirmed and made known. 



Symptoms of the disease are rarely observed until a pressure of 

 one atmosphere (15 pounds to the square inch) has been reached, 



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