PROBLEMS IN TERRESTRIAL PHYSICS. 143 



is no longer there, and that it has actually flowed off toward and over 

 regions less heated by the sun where the upper limit of the atmosphere 

 was, therefore, lower. 



7. Therefore, if the eastward movement of the surface winds in the 

 temperate regions is due to the smaller diameter of the earth in those 

 regions than at the equator, the force exerted by those surface winds 

 toward rotating the earth is not derived from the earth's rotation, but 

 indirectly from the sun, because the atmosphere in its expansion out- 

 ward and upward at the equator in the forenoon contributed by its 

 pressure toward the earth's rotation, as may be made plainer further 

 on, and its eastward movement later in the temperature regions it again 

 contributed in the same direction. 



It may be a fact, however, that those surface winds in the tropics which 

 bring air into those regions from the temperate zones, are deflected to- 

 ward the westward because of the earth's rotation. 



I would modify "the law of the winds'' as expressed by Buys Ballot — 

 viz. : "The wind blows from a region of high pressure toward one of 

 low pressure, and, owing to the rotation of the earth, is deflected to the 

 right in the northern hemisphere, and to the left in the southern." (A. 

 Guyot, page 1446 Johnson's Encyclopedia.) I would make it read : The 

 wind blows from a region of high pressure toward one of low pressure, 

 which is generally eastward because the afternoon low pressure is gener- 

 ally eastward from the forenoon high pressure. 



In response to the question,- — why does the earth rotate? a number 

 of persons have replied to me that they believe it is because of its 

 inertia, that having started rotating in that direction there is no friction 

 or resistance, therefore it continues. 



Bearing upon the smallness of the loss of motion of a planet by rea- 

 son of friction in an atmosphere of the density of that two hundred 

 miles above this earth, Sir Isaac Newton (Principia, page 401), said: 

 "The planet Jupiter, revolving in a medium of the same density with 

 that superior air, would not lose by the resistance of the medium the one 

 millionth part of its motion in one million years." 



Many years ago, Herbert Spencer suggested how the initial rotation 

 might naturally occur in the formation of a world by the falling to- 

 gether of nebulous matter, some portion of which would come with 

 greater momentum than others and thus cause rotation to begin. Thus 

 the initial rotation of our sun may be accounted for. If our earth, in 

 common with the other planets, was given ofl" from the sun, its initial 

 rotation may have been started at that time. Persons who believe the 

 present rotation to be due to inertia ought not to find it difficult to be- 

 lieve that the prevailing wind has force enough to continue the rotation. 

 But the rotation continues notwithstanding the resistance of the attrac- 

 tion of the moon and sun as exhibited in the force of the tides. I submit 

 that the force of the prevailing wind is a continuous force tending to 

 cause such continuance of rotation. 



Just how much force the prevailing wind exerts is difficult to estimate, 

 but observations on high mountains lead to the belief that above the 

 resistance offered by the trees, mountains and inequalities of and at the 

 earth's surface, the average velocity is at least fifty miles per hour, while 

 near the earth's surface it is not more than ten or twelve, and very near 

 the surface it is still less. If we suppose that the difference in velocity 



