134 SCIENCE OF COMMON THINGS. 



Effect of the inclination of the sun's rays. Natural heat 



Upon its altitude or height above the horizon / tlie 

 greater its altitude, the more perpendicularly will its 

 rays fall upon the earth, and the greater their heating 

 effect ; the less the altitude, the more obliquely will its 

 rays fall, and the less their heating effect. 



844 Why should the difference in the inclination of the sun's rays fall- 

 ing upon the earth occasion a difference in their heating effect f 



Because the more the rays are inclined, the larger 

 the space over which they fall. 



Let us suppose A B C D, Fig. 36, 

 to represent a portion of the sun's 

 rays; and C D a portion of the 

 earth's surface upon which the rays 

 fall perpendicularly, and C F and 

 C E portions of the surface upon 

 which they fall obliquely. Now, 



Fig. 36. it is obvious that the surfaces C F 



and C E are greater than the 

 Burface C D ; and as the same amount of rays of light and heat fall upon 

 all the surfaces, it is clear that they will fall more densely upon the 

 smaller surface (i.e. that it will be warmer there) and more diffusely 

 over the inclined or oblique surface (where it will be colder). 



845 What is the greatest natural heat ever observed f 



On the west coast of Africa the thermometer (Fah- 

 renheit) has been observed as high as 108 in the 

 shade / Burckhardt, in Egypt, and Humboldt, in South 

 America, observed it at 117 F. ; and, in 181 9-, at Bag- 

 dad, the thermometer rose to 120 F. in the shade. 



840 What is the lowest atmospheric temperature ever observed f 



From 60 to 70 below the zero of Fahrenheit's ther- 

 mometer. This temperature has been observed by Dr. 

 Kane and other Arctic navigators. 



84*7 What is the greatest artificial cold ever produced f 



220 below zero, which temperature was attained by 

 Prof. Natterer. At this temperature, pure alcohol and 

 ether did not freeze. 



848 What is the estimated temperature of the space above the earth's 

 atmosphere ? 



58 below zero. 



849 At what temperature does mercury freeze T 



