"28 Proceedings of the Roi/al Irish Academy. 



before they could grow large. The drops obtained were found to be very 

 uniform. 



To measure them, 100 drops were counted as they fell into a weiglied 

 beaker; about 20 were then allowed to fall on the prepared filter paper; 

 then another 100 were counted into the beaker, and the beaker weighed 

 again. The volume per drop was thus obtained. The strength of the blast 

 was then altered, giving drops of a dififercnt size, and the experiment 

 repeated. Drops varying from '04: x 10"' c.c.s to 2 x 10"-^ were obtained 

 in this way. Drops larger tlian this could be got without the blast by using 

 tubes of diflferent bores, and altering the pressure, i.e. the head of water. 

 The diameters of the stains were measured by a travelling microscope, and 

 the curve, volume of drop against diameter of stain, plotted. 



Itaiudrops taken from a great many showers have been examined, as well 

 as the stains left by some hailstones and snowflakes. No drops were got 

 from tlie lliunderslorm rain. 



The volume of the largest drops examined was about 5 x lO-" c.c.s. Drops 

 of this size — indeed, drops greater than 2-5 x 10' c.c.s— are rather excep- 

 tional, the groat majority of raindrops being smaller tlian 1 x 10"' c.c.s. 

 Some as small as '03 x 10"' c.c.s have been measured. At this stage the 

 roughness of the paper began to become comparable with tiie size of the 

 stain, rendering the stain slightly irregular, and making accurate measure- 

 ments difhcult. Drops smaller than this certainly fell. In the case of the 

 very large drops, the drop was inclined to "splash" when it fell on the 

 paper. Though the spreading of the drop generally covered this "splashing," 

 the stain was left somewhat irregular. The volume, however, could be 

 determined with a fair amount of accuracy. 



Drojjs of all sizes were found, generally very much mixed. No relation 

 was found between the charge per c.c. and the size of the drop, except that 

 in the case of the "fine" rain, which is always negatively charged, the 

 volume of the largest drop was less than 08 x 10' c.c.8. Several papers 

 exposed in this rain liave been examined, each recording hundreds of 

 drops. Only about half a dozen altogether had a volume greater than this, 

 though the largest drops on each paper were picked out and measured. 

 Small drops of this size occur in everj' kind of rain. I'apers exposed when 

 only large drops seemed to be falling showed that these small drops were 

 present. Negative rain sometimes contains as large drops as positive rain, 

 but tliere seems to be a tendency for the drops to be more uniform in the 

 case of positive rain. 



An atteuipt was made to mea.sure some snowflakes in tlie same manner. 

 They were found to consist of small weights from aliout 9 m. gms. down to 



