33^ Transactions of the Canadian Institute. [Vol. VII. 



and November a great rise occurs, the quantity of chlorine contained in 

 the air being three times as large as during the preceding months. 

 After the period of maximum there is a fall, but the chlorine remains 

 high throughout the winter months, the diminution towards the summer 

 period not commencing till April. The rain of March has yielded the 

 highest proportion of chlorine per million of water, but this is partially 

 due to the small rain-fall of this month. Rather more than two-thirds 

 of the annual supply of chlorine is contributed by the winter months." 

 And they say further in explanation : — " It would appear that in 

 summer the supply of chlorine is very limited, for a large increase in the 

 rain-fall is attended with but little rise in the quantity of chlorine 

 brought down per acre. In winter, on the other hand, the supply of 

 chlorides in the atmosphere is so constantly renewed, that an increased 

 rain- fall results in a considerable addition to the supply per acre. The 

 rather wide irregularities in the composition of the groups of rain-fall 

 for the whole year, are principally due to the different proportion of 

 summer and winter months which enters into the various groups. 



" The large excess of chlorides found in winter rain is probably due 

 in a great measure to the chlorides volatilized during the combustion of 

 fuel ; the excess in question is too uniform to be dependentxhiefly on 

 the action of strong winds blowing from the sea ; it is also remarked in 

 calm months as well as in stormy weather. Exceptionally high results 

 are, however, probably due to storms. When we turn to the nice 

 gradations observed among the winter months, it is difficult not to 

 believe that the temperature of the air has some influence on the results. 

 In the more rarified atmosphere of summer, gaseous diffusion will 

 probably be more active, while the power of transporting minute solid 

 particles will be diminished. 



" It is difficult to ascertain the influence which the direction of the 

 wind has had on the composition of a monthly rain-fall ; a partial study 

 has been made of the data at our disposal, but with no definite result." 



From this it would seem that no satisfactory explanation was then 

 known for the small amount of chlorides in the air in summer in 

 comparison with the winter months, and if we except the volatilizing of 

 sodium chloride by combustion, and the spray of the sea, there is no 

 explanation given for the chlorides being in the air at all. Both of 

 these, however, do not account for it ; but from the light of the 

 experiments of Lawes and Gilbert, and of those described in this paper, 

 the conclusion is suggested that the leaves of plants may absorb sodium 



