PROBLEMS IN TERRESTRIAL PHYSICS. 149'' 



attraction of the sun for the extra weight on that quadrant of the 

 earth causes it to fall until it reaches the most dependent position. 



As the overflow of air, caused by the advance of the heat of the sun, 

 is constant, the pressure is being applied constant!}'. It is as if the 

 tacks on the magnetic globe were brushed off at the most dependent 

 point, while at the same time other tacks were constantly being attached 

 on the descending quadrant. 



Another friend says that this would be true if the earth's axis were 

 fixed. To this it is replied that force is constantly applied to the earth 

 in more than one direction, the extra weight of the atmosphere tends to 

 bring downward toward the sun that quadrant of the earth where it is 

 forenoon, while at the same time the force of the wind is tending to 

 force upward, — from the sun — that quadrant of the earth where it is 

 afternoon. It is as if an unmounted geographical globe were constantly 

 subjected to a blast of air downward on one quadrant and upward on the 

 adjacent quadrant, the effect being to rotate the globe. A somewhat 

 similar phenomenon is seen where a spherical object is placed in an 

 upward flowing jet of water where it is maintained for a considerable 

 time rising and falling with the varying current of the water, rotating, 

 most of the time, because of the upward force of the rising stream on 

 the one side and the downward influence of the water which clings to 

 its top and falls on the other side with the rotation of the sphere. The 

 rotation results from the force acting in the different directions. Sim- 

 ilarl}- this earth rotates because of force acting in the different directions. 



Rotation implies force acting in different directions, no explanation 

 of rotation is satisfactory which does not include that idea. The extra 

 weight of atmosphere being constantly thrown on that forenoon quad- 

 rant of the earth where its effect toward rotation is greatest, combined 

 with a corresponding amount of force exerted in the other direction by 

 the fall along the earth's surface of that same extra weight as after- 

 noon wind, seems to fulfill the requirements. 



While this paper was in preparation, in reading the article in the 

 Encylopedia Britannica on tides, the following brief mention was found r 

 "There are, however, very strongly marked diurnal and semi-diurnal in- 

 equalities of the barometer due to atmospheric meteorological tides. 

 Sir William Thomson, in an interesting speculation,* shows that the 

 interaction of these quasi-tides with the sun is that of a thermo-dynamic 

 engine, whereby there is caused a minute secular acceleration of the 

 earth's rotation." 



Not finding a copy of the article by Sir William Thomson, I wrote to 

 Sir James A. Russell, of Edinburgh, who, being unable to procure a copy 

 to send me, has very kindly copied from the Society's copy and sent to 

 me such parts of it as he thought would be of interest to me : "The first 

 sentence runs — 'It has long been known, having been first, I believe^ 

 pointed out by Kant and more recently brought very near to a prac- 

 tical conclusion by Delaunay, that the earth's rotational velocity is 

 diminished by tidal agency, in virtue of the imperfect fluidity of the 

 ocean.' 



*Soci6t6de Physique, Sept. 1881, or Proc. Roy. Soc. of Edinburgh. 1881-82. p. 396. 



