CLAYTON. — THE ECLIPSE CYCLONE, 313 



external changes of temperature. The curve is traced from the record, 

 and is o-ivea on the same scale without correction in any way. The 

 eclipse be^an at Toronto about 7.47 a.m. and ended about 10.18 a.m. 

 A straight dotted Hue is drawn through the curve connecting the pres- 

 sure recorded at the beginning and end of the eclipse. It is seen that 

 the pressure was generally below the dotted line throughout the eclipse, 

 but there was an upward swell between 8 and 9 a.m., shortly preceding 

 the middle of the eclipse. Immediately preceding and following the 

 beginning and end of the eclipse the curve rises above the dotted line, 

 indicating a ring of high pressure surrounding the umbra, and thus 

 agreeing perfectly with the distribution of pressure demanded by the 

 wind circulation. I find that when the changes of pressure observed 

 during previous eclipses are separated from the normal diurnal changes, 

 they show changes very similar to those given by the curve for Toronto, 

 except that the rise in pressure near the middle of the eclipse is greater 

 for stations in the path of total eclipse. This central rise of pressure is 

 due to the increased d-ensity of the air from cold, and on it depends the 

 outflow of air surrounding the umbra. Hence in normal eclipses there 

 is a central area of relatively high pressure ; surrounding this is a ring of 

 minimum pressure, and beyond this, outside the edge of the penumbra, 

 is a ring of maximum pressure. 



The low temperature, the circulation of the winds, and the form of 

 the pressure curve accompanying the eclipse of May 28, 1900, all pro- 

 claim the development by the eclipse of a cold-air cyclone, the theory 

 of which has been so well worked out by Ferrel that no better descrip- 

 tion of it could be given than in his own words. Ferrel maintains from 

 theoretical considerations that cyclones necessarily have an inner area of 

 low pressure, surrounded by a ring of high pressure, which Professor 

 Davis has named a pericyclone. Ferrel further maintains that a cyclone 

 may liave its origin either in a high temperature increasing toward a 

 central area, or in a low temperature decreasing toward a central area. 

 The one he calls a cyclone with a warm centre, the other a cyclone with 

 a cold centre. Of cyclones with a cold centre he says : — 



" If for any reason the central part of any given portion of the atmos- 

 phere of a somewhat circular form is maintained in any way at a lower 

 temperature than the surrounding parts, and the temperature gradient on 

 all sides is somewhat symmetrical, we have approximately the conditions 

 which give rise to a cyclone. In this case it is readily seen that there 

 must be a vertical circulation, as in the ordinary cyclone, but that it is 

 reversed, out from the centre below, and in toward the centre above. 



