248 THE CHEMISTKY OF CREATION. 



mospheres. A quantity of ammonia sufficient to 

 render rain quite alkaline is occasionally present. 

 The most curious illustration of the existence 

 of such impurities in the air has been noticed 

 at Manchester. The rain which falls in that 

 city, owing to the enormous amount of mineral 

 ingredients poured by its immense chimneys 

 into the air, is found to be harder, that is, to be 

 more charged with mineral and saline ingre- 

 dients, even than the water from the neighbour- 

 ing hills, which it is now intended to use instead. 

 Occasionally an adulteration of a more sen- 

 sible character is infused into the atmosphere, 

 increases to an enormous extent, and fills the 

 air with haze. A remarkable event of this 

 kind took place in 1782. The phenomenon 

 of which we are about to speak is commonly 

 called " Dry Fog," to distinguish it from the 

 ordinary humid mist called fog. The vast space 

 between Lapland and Africa was shrouded 

 over, during the years 1782 and 1783, with a 

 dry fog unequalled in intensity. It was in the 

 form of a pale blue haze, and was so thick at 

 noon-day that the sun looked of a blood-red 

 colour through it. It was not affected by rain, 

 and it extended alike over countries, like our 

 own, of " distempered climate," and others 

 where the air is usually serene and clear. 

 Voyaging was dangerous even in the Medi- 



