172 THE WEATHER. 



would not bring it perhaps even to the heat at 

 which ice melts at the great elevations. At less 

 difference of height, the differences of resistance 

 would be less than that ; but there is a difference, 

 even for the smallest difference of height, although 

 our observation will not reach the very minute 

 cases, any more than it will reach the very 

 minutest ends in any department of observation. 

 We see as much, however, as may suffice to con- 

 vince us that the law is general; and that is all 

 which is required for the purposes of knowledge. 



The daily and annual motions of the earth (and 

 the atmosphere moves along with it) cause the 

 heat of the sun to fall differently on every place, 

 on every day in the year, and at every hour of the 

 day; and the different effects of the heat of the 

 sun on different kinds and forms of surface, farther 

 increase the variety, till the relative portions of 

 heat, at any considerable number of places, for 

 any one time, cannot be calculated with any thing 

 like certainty, or indeed at all. 



If that could be done, we should all be perfectly 

 " weather-wise," and should be able to tell how 

 the sky looked and felt in distant places, and how 

 it would look and feel at future times, with just 

 as much ease and certainty as we could state the 

 facts before our eyes. But that is an extent of 

 knowledge which no human being can by possi- 

 bility attain ; and the utmost we can expect as the 

 reward of the most careful observation, is to un- 

 derstand what is actually before us, and make a 

 shrewd but silent guess at what may immediately 

 follow. In all things the past is the only mirror 

 in which we can see the future ; and if we search 

 for knowledge of it any where else, we fail in our 



