148 THE MICHIGAN ACADEMY OF SCIENCE. 



resistance to the motion of the upper air toward or parallel with the 

 earth's sui'face, there is no force to prevent the movement of the upper 

 air from where it is midnight to where it is sunrise, except the pos- 

 sible westward flow of the upper atmosphere from a short distance 

 eastward where the sun has already begun its expansive effect. There- 

 fore the height of the atmosphere is decreased during those 'hours, the 

 pressure being least just before sunrise. Without doubt, because of 

 its inertia and the sun's attraction increasing until noon, the eastward 

 movement of the upper air continues after sunrise. This serves to ex- 

 plain why it is that, although at the surface of the earth there is not 

 apparent any way whereby so much air as passes eastward every after- 

 noon can move around the world and be ready again to pass eastward 

 the next afternoon, and so on continuously, nevertheless that it does 

 so is apparent. I think the explanation is that after midnight its east- 

 ward motion is in the upper regions. 



That the eastward movement of the air in the afternoon is not greater 

 than it is, because of the very steep gradient, is probably due to the 

 lessening effect caused by the attraction of the sun; and, combining 

 with the earth's attraction, probably that aids in causing the 10 P. M. 

 maximum pressure of the atmosphere. 



In the article in the Encylopedia Britannica on tides, the writer, on 

 page 354, says : '-Thus we see that the tidal forces tend to pull the water 

 towards and away from the moon, and to depress the water at right 

 angles to that direction. If we could consider the system as at rest, 

 we should find that the water was in equilibrium when elongated into 

 n prolate ellipsoid with its long axis directed towards and away from 

 the moon." In the diagram I offer, of the atmospheric pressure, it is 

 possible, relative to the weight of the atmosphere, to ''consider the 

 system as at rest," and it is worthy of notice that the figure of the 

 Aveight of the atmosphere has somewhat the appearance of an ellipsoid; 

 but its long axis is not directed exactly "towards and away from" the 

 sun, although if it were not for the wind,— the falling of the atmosphere 

 from the forenoon "high" to the afternoon "low" because of the superior 

 attraction of the earth, it seems that the figure might have that direction. 

 And it must be remembered that the diagram represents only the pres- 

 sure of the atmosphere, the figure of the form of the atmosphere might 

 be slightly different. 



A friend says he is unable to see how an extra load of atmosphere on 

 that part of the earth Avhere it is forenoon can tend to rotate the earth ; 

 because the extra pressure is toward the earth's center, and in no other 

 direction. 



Let us suppose a geographical globe made magnetic, and over about 

 one-fourth of its surface, that part which extends upward from the most 

 dependent part, there is placed common iron tacks. They will be at- 

 tracted by the magnetic globe and therefore will adhere, somewhat as 

 the atmosphere adheres to this earth. If the geographical globe was 

 previously of uniform weight throughout all its parts, and the axis 

 on which it is mounted is through its center of gravity, the greater 

 attraction of the eai:th for the quadrant to which the extra weight has 

 been attached will cause that quadrant to fall toward the most dependent 

 position. My view is that the principle which applies to the geographical 

 globe and this earth is applicable to the earth and the sun, — that the 



