IRRIGATION. 237 



4 grains, and in one gallon of rain water, 6 grains of calca- 

 reous matter. This is about the proportion found by Mar- 

 graff, and would give for each inch of snow water about 

 10 lbs. of salts per acre. From the existence of free acids 

 in this case, it is evident that no carbonate of ammonia could 

 have there existed. There are some experiments performed 

 by our countryman, Dr. Williams, formerly Hollis Professor 

 of mathematics and natural philosophy in Harvard College, 

 and detailed in the first volume of his History of Vermont, 

 where the experiments were performed. In 1791, 6 gallons 

 of fresh falling snow water afforded by evaporation 11 grains 

 calcareous matter, 2 grains of saline matter, 5 grains of a 

 dark brown oily matter. In January, 1792, 6 gallons of 

 snow water, from snow lying three inches deep on the grass, 

 on an area of 16 square feet, where it had lain 59 days, 

 covered with a depth of 27 inches of snow, afforded the same 

 salts as above, and 105 grains of this oily matter. This is 

 the most remarkable fact, and may afford some weight to 

 the suggestion before made, that organic matter exists gas- 

 eous in the air. It must have been drawn up by capillary 

 attraction, or evolved from the surface of the earth. It is 

 there condensed by the snow and returned to the earth, im- 

 pregnated with its salts of lime and ammonia. The snow is 

 " the poor man's manure." It not only adds salts and geine, 

 but prevents the escape of the last. But is it possible that it 

 should escape in the cold"? Doubtless it does when the 

 ground is not frozen. The snow by its warm mantle actually 

 prevents the earth growing colder, and, as has been inge- 

 niously suggested, keeps up an imperfect vegetation. The 

 snow thaws frozen ground. In 1791, Professor Williams 

 found that the ground which had been frozen 6 inches in 

 depth before the snow fell, not only had this frost extracted 

 in a few weeks by snow, but that the ground, 6 inches below 



