Chase.] 284 [December. 



The upper lines evidently embrace the warmest parts of the day, 

 and the lower lines the coolest. Dividing the day from noon to mid- 

 night, the barometer is highest when the thermometer is highest ; 

 but in the second division the high barometer prevails during the 

 coolest half of the day. 



Each of the other enumerated causes undoubtedly exerts an influ- 

 ence which must be carefully investigated before we can obtain a 

 thorough knowledge of the laws which control the atmosphere. 

 Such an investigation will probably show a mutual connection, 

 through which all the secondary causes may be referred to a single 

 force. Mr. Redfield's hypothesis, which is sufficiently indefinite and 

 general to include all the rest, was anticipated by Galileo, who 

 attributed the ocean tides " to the rotation of the earth, combined 

 with its revolution about the sun." It appears that Galileo's opinion 

 attracted little attention and led to no special investigation, partly, 

 perhaps, because it was difficult to reconcile it with the tidal inter- 

 vals, and partly because a literal as well as figurative reasoning in 

 a circle apparently demonstrated that the motions in question could 

 produce no disturbing force. I will endeavor to point out the fal- 

 lacy of this conclusion by deducing, from a reference of the aerial 

 motions to a supposed stationary earth, a law of tidal variation nearly 

 identical with the law that is derived from a consideration of the 

 relative attractions of two bodies revolving about their common 

 centre of gravity. 



On account of the combined effects of the earth's rotation and 

 revolution, each particle of air has a velocity in the direction of its 

 orbit, varying at the equator from about 65,000 miles per hour, at 

 noon, to 07,000 miles per hour at midnight. The force of rotation 

 may be readily compared with that of gravity by observing the 

 effects produced by each in twenty-four hours, the interval that 

 elapses between two successive returns of any point to the same 

 relative position witli the sun. The force of rotation producing a 

 daily motion of 24,895 miles, and the force of terrestrial gravity a 

 motion of 22,738,900 miles, the ratio of the former to the latter is 

 saVs^Voo' *^^ "00109. This ratio represents the proportionate eleva- 

 tion or depression of the barometer above or below its mean height, 

 that should be caused by the earth's rotation, and it corresponds 

 very nearly with the actual disturbance at stations near the equator. 



From Oh. to 6h. the air has a forward motion greater than that of 

 the earth, so that it tends to fly away; its pressure is therefore 

 diminished, and the mercury falls. From 6h. to 12h. the earth's 



