goyne, R.E., then Chairman of the Board of Public Works in Dublin, gives the result of experiments on a rectangular syphon tube with a section of six inches wide by one-and-a-half inch deep, or area of nine square inches. The length of the syphon is not given, but from the drawings given we infer it to be 30 inches, and of the general form given in diagrams 1, 2 and 3, Fig. 43a, but "slightly bell-mouthed" at the "entrance and discharging terminations." A straight tube of the same length and form was made, and the time of discharging 24 cubic feet of water from each with the same heads was as follows: : The head of 10 inches gives by calculation from these experiments, 860 for the coefficient of discharge due to the bend over the crest; and the head of 131⁄2 inches, a coefficient of 874; which shows that the resistance from the bend was less for a greater velocity. Mr. Mallet also found that with an effective head of 8 inches, 24 cubic feet were discharged in 89 seconds. This gives, by calculation, the coefficient 658 for all the resistances due to the orifice of entry friction in the tube and bends. Taking the coefficient of the bend here at 850 as due to a lesser head, this gives 774 for that due to friction and the orifice of entry. Another experiment, with a head of 11 inches, gave a discharge of 24 cubic feet in 78 seconds. This is equivalent to a coefficient of 636 for all resistances, and dividing by 860 for the bend, 740 is found for the friction and orifice of entry. Again The effective head here to calculate the results from, exceeds by inch or half the depth of the tube, that taken by Mr. Mallet, as in the effective head taken by him this is omitted, but the 8-inch head agrees with that he has taken, the error being eliminated by taking a difference. Taking the mean general coefficient of these results at 636, the discharge is expressed by the equation (154b.) d = 481·5 × ·636 a √ ƒ = 306 a √ƒ, the discharge in cubic feet per minute for feet measures. This is less than that before given by our eqn. (154a) by about 3 per cent. The application of the syphon for the discharge of surplus waters is of great value, and the head can be increased to any extent not exceeding the difference of level between the upper and lower water. It is not the object here to enter into the question of construction, or the means of withdrawing the air or putting the apparatus to work, but a comparison between its advantages, lifting-sluices, and Les Barrages Hausses Mobiles has been already entered into at p. 291. CHANNELS.-DISCHARGE FROM SEWERS.-LOSS FROM EVAPORATION, ETC. A catchment basin is a district which drains itself into a river and its tributaries. It is bounded generally by the summits of the neighbouring hills, ridges, or high lands forming the water-shed boundary; and may vary in extent from a few square miles to many thousands; that of the Shannon is 4,544 square miles. The average quantity of water which discharges itself into a river will, cæteris paribus, depend on the extent of its catchment basin, and the whole quantity of rain discharged on the area of the catchment basin, including lakes and rivers. THE QUANTITY OF RAIN which falls annually varies with the district and the year; and it also varies at different parts of the same district. The average quantity in Ireland may be taken at about 34 inches deep, that which falls in Dublin being 27 inches, in Armagh, average of 14 years, 35 inches; in Killaloe, average of 17 years, 43 inches; in Galway, average of 11 years, 46 inches; and that in Cork 41 inches nearly. The average yearly fall in Dublin for seven years, ending with 1849, was 26 407 inches; and the maximum fall in any month took place in April, 1846, being 5.082 inches. "The average fall in inches per month for seven years, ending with 1849, was as follows:-October, 3.060; August, 2:936; January, |