60 DR DAVY ON THE RAIN-FALL IN THE LAKE-DISTRICT. 



15. November the Ith. — During the last twenty-four hours -05 inch of rain ; 

 the wind northerly ; sky overcast ; showers. A rain-drop left a just perceptible 

 marginal stain, which w^as of a brownish tinge, and was darkened by exposure to 

 a charring heat. 



These results may suffice to show the use of the microscope in this inquiry. 

 I shall defer any remarks on them for the concluding parts of my paper. 



Of the results obtained by the use of the nitrate of silver, which was so con- 

 stantly employed, I must limit myself to a brief account ; and, as in a large 

 number of instances a portion of the water tested — a measured portion, such as 

 that specified — was evaporated for microscopical examination, it will be proper 

 to conjoin a notice of the results thus obtained. 



The following is a classification of the results, according to the degree of effects, 

 that is, of cloudiness and precipitation, by means of the nitrate of silver. The 

 trials made were 217 in number. 



1. In 10, there was no visible effect. 



2. In 29, the effect was just visible. 



3. In 70, it was slight, and very slight. 



4. In 57, it was moderate. 



5. In 43, it was considerable. 



6. In 8, it was strongly marked. 



The circumstances as to wind and weather under which these results were 

 obtained, were of course extremely various, nor were they always well defined in 

 relation to the effect. I shall offer a few brief comments on each class. 



1. The ten instances in which no effect was visible, the rain-water remaining 

 perfectly clear after the addition of the solution of nitrate of silver, afford a 

 striking example of the remark just made. In the larger number the atmosphere 

 was calm, the quantity of rain small ; in the smaller number there was a con- 

 siderable fall of rain ; the wind was gentle or moderate, and from the N.W. ; in 

 one instance it was strong and from the south, and accompanied with much rain. 

 Though no chlorine or other substance was present appreciable as a precipitate 

 by nitrate of silver, jQt in one or two trials there was a slight discoloration of 

 the water produced after exposure to light, indicative of the presence of organised 

 matter. And in two or three instances that a portion of the water was evapo- 

 rated, a residue or faint stain was obtained, which in one, as seen under the 

 microscope, consisted of extremely minute granules ; in the other two, of granules 

 and of delicate stellate crystallisations. 



2. In the twenty-nine instances in which the effect was only just visible, the 

 circumstances of weather were even more various than in the last. Most fre- 

 quently the wind was from the N., N.E., or N.W., and oftener gentle than strong, 

 and with little rain. The water, when evaporated, yielded commonly a stain or 

 residue very similar to the preceding. 



