MIASMATA. 189 



dall pillar of light was well defined. It continued a long 

 time apparently little increased in size, and without having 

 acquired much brilliancy. At length its sides near the bot- 

 tom gave way, and the light, now stronger, dilfused itself 

 laterally to a considerable extent. By-and-by the stratum of 

 clouds immediately over this expansion displayed the roseate 

 hue of morn, and the whole heavens became (though yet 

 faintly) illuminated. The rosy tints, disappearing in their 

 turn, were succeeded by a greater degree of pale light, 

 and soon after the near approach of the great luminary him- 

 self was announced by a pillar of red or orange-red light, 

 which terminated in the orb, now appearing large and fiery, 

 through the medium of the horizontal morning air. This 

 is the general course of sunrise in India, as I have often 

 witnessed since. The precursoiy phenomenon of the pil- 

 lar of light, with the successive changes, being then new to 

 me, appeared perhaps more interesting on that account." 



This pillar of light is the zodiacal light of astronomers, 

 which we find first mentioned in modern times by Childraus 

 in the year 1559. After his observation had been recorded, it 

 was entirely forgotten until again seen by Cassini on the 

 18th March, 1683. Since that period its appearance is often 

 recorded by naturalists. Its nature is not well understood. 

 Cassini, Mairan, Euler, Laplace, Regnier, Hube, and 

 Hahn have speculated with more or less plausibility in re- 

 gard to it. 



IS. Miasmata. — Under this name we understand that 

 matter or those matters which, emanating from marshes 

 and other situations where organic bodies are in a state of 

 decomposition, and received into the human system, produce 

 disease, particularly remittent and intermittent fevers, &c. 

 A moderate degree of heat is necessarv' for the formation 

 of this poison, and also a moderate quantity of moisture. 

 Low situations are more exposed than high ones to miasm, 

 as it is formed at the earth's surface, and as it rises up- 

 wards becoming more and more diluted with pure air. 

 Thus the inhabitants of the Campagna di Roma retreat on 

 the approach of the sickly season to the higher grounds, 

 and consider it dangerous to sleep in the lower apartments 

 of a house. Stagnation of the air sometimes allows dan- 

 gerous accumulations of raiasmatous matter ; the growth 

 of underwood is very favourable to its accumulation, by 



