170 MONTHLY JOURNAL OF AGRICULTURE. 



water during drouth and heat is so much more essential, this difference in the 

 richness of water is not so visib)' observed. 



In using small streams, on considerable acclivities, by catch-ivork as represent- 

 ed in fig. 1, temporary means of diverting the water from the main channel may 

 be resorted to, and there can possibly be a failure. But, in larger streams, the 

 work should always be well formed at once. A good permanent dam must be 

 made, and substantial hatches, or solid framework furnished with a sliding grate, 

 inserted, in using small streams, many diverging channels may be cut ; in large 

 ones this cannot be done, from the cost of many large dams ; a single dam may, 

 therefore, be used, from which a main side channel should pass, to be subdivided 

 according to the circumstances of the case. 



Irrigation Avill always need an exercise of the judgment, to be done in the best 

 manner ; no two pieces of land being exactly alike, and the irregularities of the 

 surface varying in many ways, the plan of the work or the distribution of the 

 channels must vary. Each, therefore, requires a different design, adapted to the 

 circumstances of the case. But no one should be deterred from an attempt, nor 

 lose the eminent advantages of irrigating his grounds, because he cannot attain 

 perfection at once. 



It is sometimes objected to watering grass and other lands, that the crop, 

 though greatly increased in quantity, is lessened in quality. This is indeed true 

 to a small degree, but not more so than results from an increased growth by sta- 

 ble manure. The slight inferiority in quality is immeasurably overbalanced by 

 the increase in bulk. No objector would desire his hay crop to be lessened one- 

 half in quantity by a parching drouth, in order that the hay might be better. 



Application to Different Crops. — Irrigation is usually applied to grass land, 

 but there appears to be no reason why it may not be greatly advantageous if used 

 for different cultivated crops during our hot summers. S. Williams, of VVaterloo, 

 IN. Y. states that, during a severe drouth, he admitted water in small gutters be- 

 tween the hills and rows of vegetables in his garden. " In ten days, early pota- 

 toes grew two-thirds in size." In fact, he never obtained good potatoes before. 

 Other vegetables were greatly benefited. The great increase by watering, in the 

 growth of spinach, lettuce and strawberries, by the English and Flemish garden- 

 ers, is well known. In a warmer climate, the advantages would be increased. 

 "The melon," says Lindley, "acquires its highest excellence in countries where 

 its roots are always immersed in water, as in the floating islands of Cashmere, 

 the irrigated fields of Persia, and the springy river beds of India." But the same 

 experiments were not attended with such success in London, where the leaves 

 perspire less, and the climate is cooler. During the past summer, raspberry 

 plants, watered by the drippings from the eaves of a workhouse, grew triple the 

 size of others deprived of this advantage. 



But as all plants are rendered more succulent by watering, the supply of water 

 should be withheld to all that bear fruit, as the period of maturity approaches, 

 or diminished fiavor will be the consequence. 



Calculating the Velocity of Water in Channels. — It often becomes a mat- 

 ter of some consequence, not only in cutting channels for irrigation, but for sur- 

 face drains in reclaiming wet lands, to know the exact amount of water which 

 may be carried with a given descent in the stream. To enable any person to cal- 

 culate this readily, the following rule is given, and may be readily used by any 

 boy who understands common arithmetic. 



To ascertain the mean velocity of iratei' in a caiial or river Jlowing through a 

 straight channel of et/ual size throughout : 



Let /= the fall in one English mile in inches ; 



Let d =^ the hydraulic mean depth ; 



Let V = the velocity in inches per second, then 



V = 1 . 23\/df- 



The hydraulic mean depth is a quantity which, when multiplied by the perim- 

 eter of the channel in contact with the water, gives an area equal to the area of 

 the section. 



Example: Suppose a furrow is cut six inches wide and four inches deep, with 

 perpendicular sides, and that it descends one inch in a rod : to tind the quantity 

 (a62) 



