Periodicity of insalubrious Conditions. 97 



invariably prejudicial. At these times light variable winds 

 alternate with thunder-showers, after which there is usually 

 experienced great heat by solar radiation, which at once 

 liberates the noxious emanations of the humid soil. Further 

 on, during the actual rain}^ season, when the heavens are 

 almost continually veiled, and the <}ondition of the atmo- 

 sphere and the soil is alike one of comj^lete saturation, this 

 phenomenon appears much less marked, and becomes in a 

 corresponding degree less dangerous to human organization. 



We are also of opinion that the time from the end of March 

 to the end of April, as also the months of September and 

 October, are the most insalubrious parts of the year, although 

 on the Nicobars a man may be struck down with fever at any 

 season, so soon as those precautions have been neglected, 

 which are so necessary to observe in the uncultivated regions 

 of the tropics. An instance on this point is furnished in the 

 case of the crew of the Danish corvette Galatea. Of thirty 

 individuals engaged in an exploring expedition up what is 

 known as the Galatea river, in the southern Bay of Great 

 Nicobar, and caught one night in a thunder-storm, which 

 compelled them to remain in the forest wringing wet, no 

 fewer than twent3^-one fell ill of fever, which ultimately 

 proved fatal in four cases. 



So far as our own experience goes, the state of health on 

 board the frigate during a stay of thirt3^-two days was highly 

 satisfactory. During that entire period, out of 350 men only 

 six took ill with fever, which number, however, at a later 



VOL. II. II 



