1864.] Note on the Hailstorm of TJmrsday the 24th March. 533 



southerly current would cause a sudden rise of hoth into the higher 

 regions of the atmosphere, and if this were very rapid the reduction in 

 the temperature consequent upon the expansion of the heated air, aided 

 by the cooling influence of the northerly current, might, I think, reduce 

 the temperature sufficiently to cause the formation of hail. That such 

 an upward current existed, is, I think, proved by the barometrical 

 reading, which at 6 o'clock (2 hours after the afternoon minimum) 

 gave a reading of 29.712 inches, whereas the corresponding morning 

 reading was 29.811. At the usual period of the afternoon minimum 

 (4 o'clock) the pressure was 29.719, at the morning minimum 29.769. 



The clouds were not low during any part of the storm, but it is 

 scarcely probable that the hail was produced in their lower strata. 

 The quantity of rain which accompanied the hail was greater than 

 could well result from the mere partial liquifaction of the hail-stones, 

 and I am inclined therefore to infer, that rain fell from the lower strata 

 of cloud, the formation of hail being confined to the upper portions of 

 the mass. 



The uniformly concentric structure of such stones as that delineated 

 in fig. 2a, and the air-bubbles of the clear portion, afford interesting in- 

 dications of the mode of formation of the hail-stones. The clear ice 

 must have been condensed in the fluid form, and have contained a large 

 amount of air in solution, which, as in the formation of lake ice, was 

 squeezed out at the instant of solidification, forming the air-bubbles now 

 entangled. The concentric zones indicate so many atmospheric strata 

 of condensation and it is probable that they consist of radiating snow 

 spicules i, e. ice condensed from vapour below the freezing point, and 

 crystallizing on a solid nucleus, instead of forming free flakes. On this 

 view each clear zone represents a portion of the stone formed in an 

 atmosphere above the freezing point, and subsequently frozen, while 

 each opaque zone represents that contributed by an atmosphere below 

 32 . This would shew a great variability in the upper strata of cloud, 

 but such might result from the eddying of the mingling currents. 



The oblate or discoid form of the stones and their axial hollows are 

 more difficult to explain. Were they in rapid rotation, they might 

 indeed acquire the observed form by centrifugal force, but there is no 

 apparent reason why such a motion should be set up. I do not know 

 that a similar observation has been previously recorded, but the pre- 

 valence of the phenomenon in the case of the hail-stones in the storm 



