ATMOSPHE^ROLOGY. 379 



material elevation of temperature ; but when they 

 impinge on the black exterior of a ship, the pitch on 

 One side occasionally becomes fluid, while ice is ra- 

 pidly generated on the other ; or while a thermome- 

 ter, placed against the black paint-work on which 

 the sun shines, indicates a temperature of 80 or 90 

 degrees, or even more, on the opposite side of the 

 ship a cold of 20 degrees is sometimes found to pre- 

 vail. 



This remarkable force of the sun's rays, is accom- 

 panied with a corresponding intensity of light. A 

 person placed in the centre of a field or other compact 

 body of ice, under a cloudless atmosphere and ele- 

 vated sun, experiences such an extraordinary inten- 

 sity of light, that, if it be encountered for any 

 length of time, is not only productive of a most pain- 

 ful sensation in the eyes, but sometimes of tempora- 

 ry, or even, as I have heard, of permanent blindness. 

 Under such circumstances, the use of green glasses 

 affords a most agreeable relief Some of the Indi- 

 ans in North America defend their eyes by the use 

 of a kind of wooden spectacles, having, instead of 

 glasses, a narrow perpendicular slit, opposite to each 

 eye. This simple contrivance, which intercepts, 

 perhaps, nine-tenths of the light that would reach 

 a ndked eye, prevents any painful consequences from 

 the most intense reflection of light that ever oc- 

 curs. 



