276 CJironicIes of Science. [April, 



spherical pressure at the sea level are first discussed, on the basis of 

 all trustworthy observations which were accessible, and then the 

 prevailing winds are similarly treated, but with reference only to 

 direction, not to force. The results obtained are entered on charts 

 for each month and for the year. The broad facts arrived at are 

 that the wind flows in accordance with Buys Ballot's Law around 

 the areas of barometrical depression and elevation, the motion being 

 retrograde in the first case, direct in the other, and that it does not 

 flow as a constant anti-trade at the earth's surface in high latitudes, 

 as supposed by Maury. The position of the respective areas of 

 barometrical disturbance varies very considerably from month to 

 month, and is mainly determined by the thermal conditions of the 

 globe at the respective seasons. 



It will be seen that the ideas of Mr. Buchan are somewhat at 

 variance with Dove's theory of the paramount importance of the 

 Polar and Equatorial currents (as N.E. and S.W. winds) in regu- 

 lating climates. He has, however, submitted this theory to a special 

 test, as on calculating the directions of the prevailing winds at each 

 station he finds that almost always there are two maximum directions 

 shown, but that in only 30 per cent, of the stations do these direc- 

 tions belong to either of the above-named winds ; so that it cannot 

 be maintained that there is a general flow of the winds of the North 

 Temperate Zone towards and from the Polar regions. 



In the theoretical explanation of air-motion, given by Mr. Buchan, 

 the chain of reasoning is not perfectly conclusive. He argues in this 

 way : if motion in the lower strata of the atmosphere be in a definite 

 direction, a compensating movement must exist at an upper level. 

 The lower currents are determined by the course of the isobaric 

 lines, therefore the upper currents may be inferred from these same 

 lines " taken reversely together with the isothermal lioes taken 

 directly." He assumes that if, over any area, temperature near the 

 ground be low, it must necessarily follow that pressure at a great 

 height over the same area must be much reduced. This may perhaps 

 be true, but it is far from being as yet proved, in the utter absence 

 of the possibility of any experimental confirmation of the statement, 

 as we know nothing of the vertical distribution of pressure. 



Taking the paper as a whole, it is one of the most valuable con- 

 tributions to the science which has appeared of late years, and the 

 least that can be said of it is that the results are fully commensu- 

 rate with the labour bestowed on the discussion. 



The other paper to which we have referred is one by Dr. Julius 

 Hann, " On the Winds of the Northern Hemisphere and their In- 

 fluence on Climate," read before the Yienna Academy. In the first 

 part of this discussion the wind-systems are explained on the hypo- 

 thesis of Dove's two currents ; the Equatorial, flowing over the sea ; 

 and the Polar over the land : but the variations in their respective 



