It has long been recognized that the source of chlorine in rainfalls near the sea was the sea itself, the amount of chlorides, putting aside local exceptions arising from cities or manufactories, increasing with the proximity of the point of observation to the ocean, and also showing a marked relation to the exposure of the position chosen to violent storms.  Thus the west coast rainfalls of Ireland contain larger quantities of chlorides than those of the east, and the table given by Dr. Smith shows the variations in neighboring localities on the same seafront.  The chlorides of the English rains diminish as the observer leaves the sea coast.  In the following observations the waters of thirty-two rains were collected, the chlorine determined by nitrate of silver in amounts of the water varying from one liter to one-half a liter, and in some instances less.  While it is likely that some of the chlorine was due to the presence of chlorides other than common salt, as the position of the point of observation is not removed more than a mile from oil distilleries and smelting and sulphuric acid works in New Jersey, yet this could not even generally have been so, as the rain storms came, for the greater number of instances, from the east, in an opposite direction to the position of the factories alluded to.  It has also been noticed by Mr. A. Hollick, to whom these observations were of interest, that in heavy storms a salt film often forms upon fruit exposed to the easterly gales upon the shores of the island.

The yearly average for chlorine is 0.228 grain per gallon; for sodic chloride, 0.376 grain.  The total rainfall in our region for 1884, as reported by Dr. Draper at Central Park, was 52.25 inches, somewhat higher than usual, as the average for a series of years before gives 46 inches; but taking these former figures, we find that for that year (1884) each acre of ground received, accepting the results obtained by my examination, 76.24 avoirdupois pounds of common salt, if we regard the entire chlorine contents of the rains as due to that body, or 46.23 pounds of chlorine alone.

In comparison with this result, we find that at Caen, in France, an examination of the saline ingredients of the rain gave for one year about 85 pounds of mineral matter per acre, of which 40 pounds were regarded as common salt.

Although chlorine is almost constantly present in plant tissues, it is not indispensable for most plants, and for those assimilating it in small amounts, our rainfall would seem to offer an ample supply.  These facts open our eyes to the possible fertilizing influence of rains, and they also suggest to what extent rains may exert a corrosive action when they descend charged with acid vapors.—­L.P.  Gratacap, in School of Mines Quarterly.

* * * * *

THE CHROMATOSCOPE.