1864.] 367 [Chase. 



Mr. Cliase made remarks upon the subject of magnetism, 

 and in further illustration of what he had advanced at pre- 

 vious meetings. 



Barlow's and Lecount's laws for the distribution of the induced 

 magnetism in masses of iron, are precisely the same as would follow 

 from the relative centrifugal motions of different portions of the 

 earth, provided the magnetic axis coincided with the axis of rotation. 

 It is therefore reasonable to presume that they accurately represent 

 the superficial motions or currents on which the magnetism depends, 

 and to hope that a careful study will enable us to detect the cause 

 of the oscillations that polarize the air and all other bodies that are 

 capable of vibrating in harmony with it. 



If the earth were stationary, the sun's heat would produce a con- 

 stant ascending current over the whole meridian, which would be 

 supplied by colder lateral currents from each side. fig.i. 



These currents are represented in Fig. 1. P, is the pole; w i \ / 

 E, the equator ; a, h, c, the lateral currents. The light A I A 

 arrows represent the direction of the upper, overflowing, 

 warm air, and the dark ones the direction of the lower, *,^N< \*^ 

 cool air. The effect of these several currents would be 

 a mechanical atmospheric polarity, precisely analogous '^ ^_^\^^^ 

 to that which was indicated by our experiments upon the k 



control of the magnetic needle by mechanical vibrations. 



In consequence of the earth's rotation, the tendency shown in Fig. 

 1, is communicated only at the instant of noon. At all other times, 

 the flow of the cool air towards the equator, and of the warm air to 

 the coldest portions of the globe, is modified by the earth's motion, 

 so as to produce currents analogous to those represented in 

 Fig. 2. P represents, in this instance, not the true pole, 

 but the point of greatest cold. The warm air rises at E, and ' 

 flows towards P until it becomes sufiiciently cooled to sink 

 to the earth. Still flowing onward it absorbs the heat of 

 the earth, until it is so rarefied as to rise again. This pro- 

 cess of alternate rise and fall, is continued until the air 

 reaches P, and then returns by the same law and in a similar man- 

 ner, to E.* These currents, which are flowing at all hours, and in 



* Halley, in 1686 (Phil. Trans., No. 183), e.xplained the trade wind, and the 

 necessity of a reverse upper current, but he found it " very hard to conceive why 

 the limits of the trade wind should be fixt about the 30th degree of latitude 



