EECEEATIVE SCIENCE, 



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ease become if we confine our remarks to any 

 particular locality, for we shall there find con- 

 stant changes within certain limits. The pres- 

 sure may be as light as 28 inches, or as heavy 

 as 31 inches, at the sea-leyel ; but it cannot be, 

 for example, as little as 26 inches, or as great 

 as 32 inches. Here, then, we have certain 

 limits for the pressure of the atmosphere ; 

 and if the barometer rises in one locality, it 

 must necessarily fall in another, as the pres- 

 «ure from one spot must be added to another- 

 With regard to temperature, a certain degree 

 of heat is given to our globe from the sun, 

 always the same under similar circumstances, 

 but very different in difierent localities, and 

 varying in a remarkable degree, in the same 

 spot, from time to time. As an instance, the 

 temperature in the shade, in winter, in Great 

 Britain, has been known to be 60° lower in 

 one year than at the same period in another. 

 One great cause in the alteration of tempera- 

 ture depends on the position of the sun with 

 regard to a particular country ; the more 

 vertical the sun becomes, the higher the tem- 

 perature rises, whilst the nearer the sun ap- 

 proaches the horizon, the less heat does that 

 particular locality receive ; hence arises our 

 summer's heat and our winter's cold. Know- 

 ing this fact, it becomes evident that whilst 

 it is winter in the one hemisphere, it must 

 necessarily be summer in the other. But 

 the winters are not always alike. We have 

 cold winters, and we have those that are 

 warm ; nevertheless, the same temperature is 

 received from the sun every winter in each 

 hemisphere. It is simply colder in one portion 

 of that hemisphere than in another j and if 

 heat is robbed from one particular spot, it 

 must become accumiJated at another. Thus, 

 we find that last winter was excessively severe 

 in North America, whilst England experi- 

 enced mild weather. It seems as if the great 

 cold of the polar regions became master of 

 the feeble heat of the winter's sun; and, 

 under these circumstances, we are at the 

 mercy of the winds which bring the cold from 



the icy sunless districts; they may either 

 carry this icy influence over us, or avert it 

 in another direction. 



The same law which governs planetary 

 movements seems to hold good with regard 

 to wind, namely, the^r*^ impulse which pro- 

 pelled a planet in a straight line directly 

 away from the sun, and the power of gra- 

 vitation, which exerts an influence in the 

 opposite direction ; the two forces combined 

 producing nearly circular motion. Asillus- 



Fi(j. \. 



tration, see Pig. 1, where i j, k l, M N, o P, 

 represent the first impulse, and J i, l K, N m, 

 p o, the power of gravitation, these two in- 

 fluences moving a body in the direction A B, 

 B c, o D, along the arc e r g h. 



The polar currents set in straight linea 

 toward the equator, they meet the resist- 

 ance of the earth rotating on its axis and 

 become bent, whilst the equatorial currents 

 set in straight lines towards the poles, and 

 are also bent by the earth's rotation, the 

 former creeping along the ground, and rising 

 higher as they approach the equator, and the 

 latter moving at a great height, yet becoming 

 lower as they approach the poles, the two 

 currents mingling together in the regions of 

 variable winds. The same current, from the 



