ON THE STORM OF THE 18TH OF APRIL, 1850. 315 



southward of the others ; there are, however, two large trees in the 

 garden lying side by side, but in directions diametrically opposed. 



It has been stated that in the College Park the shifting of the 

 wind amounted to 180 ; and it has been inferred that the centre 

 of the vortex passed over that spot. From what has been said as 

 to the nature of % the phenomenon, it will follow that in other 

 localities, over which the vortex did not pass centrally, the wind 

 must have shifted through different points of the compass, and 

 through angles smaller in proportion to their distances from the 

 centre. Thus, on the southern side of the line described by the 

 centre of the vortex, the change of the wind should be from south 

 to west, and on the northern side of the same line from east to north. 

 We are not yet in possession of facts which bear upon this point ; 

 but from the limited dimensions of the vortex, and the consequent 

 smallness of the distance necessary to produce such a variation, it 

 is probable that evidence bearing upon it may be obtained. I 

 shall only observe that, in seeking and comparing such evidence, 

 care must be taken not to confound eddies arising from local 

 obstructions with the general direction of the current. 



The hours of observation at the Magnetical Observatory are 

 7 A. M., 10, 1 P. M., 4, 7, 10. The observations of the barometer, 

 and of the dry and wet thermometers, made at these hours on the 

 day of the storm, are the following : 



The fall of rain, and melted hail, in Trinity College during the 

 storm amounted to 0'596 of an inch ; but it is probable that much of 

 the hail was driven out of the receiver of the gauge by the wind. 



It will be seen that the barometric fluctuation is small. It is 

 stated, however, that a sudden and considerable fall of the 

 barometer took place shortly before the storm. From the obser- 



