162 Dr. Waller's additional Observations on Hail, 



Ksemtz's Meteorology). I am not aware that the origin of this 

 vegetation in snow has ever been satisfactorily accounted for; 

 but when we consider how widely this vegetation is diffused, 

 and the depth to which it penetrates, it does not appear un- 

 likely that it may have fallen with the snow, in the same man- 

 ner as the organic bodies in hail are brought from the upper 

 I'egions of the atmosphere. Further observations must deter- 

 mine how far these surmises are correct, and whether these 

 bodies are not the same in both cases. 



Again, in the hands of Ehrenberg the microscope has been 

 the means of detecting, in dust fallen on ships in the Atlantic, 

 the remains of above sixty different species of infusoria, Mr. 

 Darwin, in his interesting paper in the Transactions of the 

 Geological Society, mentions that dust has been collected in 

 this manner at a point midway between Senegal and Cayenne. 

 The distance to which volcanic ashes may be conveyed by the 

 higher atmospheric currents, in a direction contrary to that 

 of the lower prevailing winds, is well known. These facts 

 being duly weighed, the frequent and even habitual existence 

 of minute cryptogamic s})orules and infusorian ovules in the 

 higher regions of the atmosphere, where hail is formed, will 

 not appear more incredible than the continued suspension 

 of globules of water composing clouds ; which globules, 

 as measured by diffraction, are found of far greater size than 

 the former. The relation between the presence of these par- 

 ticles and other phaenomena of meteorology remains to be 

 determined, and how far they may be regarded as accom- 

 panying and detector agents of other atmospheric conditions 

 following or preceding them ; and whether the infusoria and 

 the cryptogamia are the same at all seasons of the year; 

 whether the locality in which they are collected has any influ- 

 ence; and lastly, whether they are the same in hail and water 

 falling at about the same time. 



In meteorology water likewise presents itself in what is 

 termed the vesicular, as in clouds and fogs, in the condition 

 of rain, snow and frost. In a paper which was read before 

 the Royal Society, and which will appear in the Philosophical 

 Transactions, 1847, will be found some experiments of mine 

 upon water in the first-mentioned condition ; with regard to 

 the others I shall confine myself to the following remarks. 



The transformation of fogs into rain is frequently taking 

 place around us. Fogs, which at first are what is termed dry 

 fogs, scarcely possessing the power of moistening surrounding 

 objects, alter a time are found to deposit numerous small glo- 

 bules of water, which as long as they remain attached to mi- 

 nute filaments retain their spherical form, but when in con- 



