44 



Prof. James Thomson. 



[Mar. 10, 



A short sketch of such progressive researches is given in the 

 paper. 



Also through information derived from observational sources, it 

 came gradually to be accepted, as an established fact, that in the 

 latitudes outside the limits of the trade winds — latitudes extending 

 from about 28° or 30° up to far towards the poles — the wind, while 

 prevailing- from the west, as had been previously known, prevails also 

 more from the equator towards the pole than from the pole toward;' 

 the equator, so that to take the case of the northern hemisphere, fo.» 

 simplicitv, the winds of our middle latitudes were found prevalently 

 to blow from south of west. 



To account for this component from the south in these westerly 

 winds, it came to be very generally supposed among the best writers 

 on the subject that the air departing for the northern hemisphere 

 from the top of the equatorial belt of buoyant air, while flowing 

 northward still in the lofty regions of the atmosphere and over the 

 trade- wind zone ; soon becomes a current from the south-west, or from 

 south of west, and continues, after descending to the earth's surface 

 at the northern border of the trade- wind region, still to move forward 

 in continuation of its old course as a current from south of west. 

 But why in the lower regions a poleward motion should be maintained 

 rather than a return flow towards the equator, and how the return 

 from higher to lower latitudes, to compensate for this supposed 

 poleward surface current, should be accomplished, are questions 

 which appear to have been scarcely mooted or to have been left en- 

 shrouded in vagueness. 



The paper goes on to give an account of the theory which Maury 

 offered in 1855 as an attempt to clear up what he considered "para- 

 doxical " in the theories of others on this subject. 



The author of the paper presently reported in abstract (Professor 

 James Thomson), finding Maury's theory untenable, devised a new 

 theory in 1857, and brought it forward at the Dublin meeting of the 

 British Association in that year. In endeavouring to penetrate the 

 mystery as to what the courses of the circulation might be in the 

 middle and higher latitudes, he was, in preliminary ways, fully 

 satisfied that Hadley's theory, in its main features, must be substan- 

 tially true, and must form, the basis of any tenable theory that could 

 be devised. He adopted that theory in all its important features, and 

 superadded further new features, which are told of at length in the 

 paper. His theory, so composed, may be briefly sketched out as 

 follows : — 



That at the equator, or near to it, there is a belt of air ascending 

 because of its high temperature and consequent rarefaction : — that 

 its supply of air is maintained by influx from both sides towards the 

 zonal region at its base, which is a region of diminished pressure : — 



