382 RECORD OF SCIENCE FOR 1887 AND 1888. 



This result following diioctly from Ibe computation and at first sur- 

 prising finds its confirmation in a variety of observations. For example 

 ill England we observe a deviation of Gl degrees for land winds but of 

 77 degrees for sea breezes. From this it follows that the friction on 

 the land is more than twice as great as on the sea. 



Conditions of pressure like those here considered frequently occur. 

 In the regions of the trade winds and monsoons they ordinarily prevail 

 either during the whole or about half of the year. 



The circular isobars to the consideration of which we now pass pro- 

 duce systems of wind that can be considered as the simplest types of 

 cyclones and anti cyclones according as the pressure in the interior is a 

 minimum or maximum. We confine ourselves here to the consideration 

 of cyclones. 



As already remarked, these are not conceivable without an ascending 

 current of air, whose area in our case is defined by a circle. Outside 

 of this horizontal movements prevail exclusively; inside of it there is 

 also the vertical movement to be considered. Therefore the comi)uta- 

 tions for the outer and inner regions are different. In this way we ob- 

 tain the following results : 



(1) The pressure increases from all sides outward from the center ; the 

 gradient increases also from the center out to the limit of the inner re- 

 gion ; from there on it diminishes, and at a great distance becomes in- 

 appreciable. 



(2) The wind-paths in both regions are curved lines, logarithmic 

 spirals, which cut the isobars everywhere at the same angle or make 

 everywhere the same angle with the radial gradient. Therefore the 

 movement of the air can be considered as consisting of a current toward 

 the center and a rotation around the center, the direction of the latter 

 is counter clock- wise. This departure from the gradient is of different 

 magnitudes in the outer and inner regions. For the former the de- 

 parture has the same value as for straight isobars, that is to say, it 

 depends alone upon the rotation of the earth and the friction. For 

 the inner region the departure is greater, and depends besides upon the 

 intensity of the ascending current of air. If both regions were sepa- 

 rated from each other by a geometrical cylindrical surface, then the 

 wind-paths in these would not continuously merge into each other, but 

 would form an angle with each other. This, of course, can never occur 

 in nature. We must therefore assume a transition region in which the 

 wind is continuously diverted from one into the other direction. At 

 any rate accurate and comparative observations of the wind direction 

 in the inner and outer region of a cyclone would be of great interest. 

 From these one could draw a conclusion as to the limitation of the as- 

 cending current of air. This limit is, moreover, also notable in that at 

 it the winds reach their greatest force. 



There is no arrangement that has been discussed theoretically as yet, 

 except the straight line, circular, and nearly circular forms of the 

 isobars. 



