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Some facts bearing upon Irrigation.

By H. C. RUSSELL, B.A., F.R.A.S., Government Astronomer.

[Read before the Royal Society of N.S.W., 5 September, 1883.]

So much has recently been said about the irrigation of the interior of this Colony that I am induced to publish now some first. results of experiments I have in progress, for the purpose of ascertaining how much water is lost by evaporation from grassed land, and also from cultivated land.

The investigation of this subject is usually left to the agriculturist, and we have no recognized standard instruments with which to proceed. But I take a deep interest in the water that. falls as rain, and I am anxious to know what becomes of it. At present I am endeavouring to find how much goes to supply vegetation and evaporation, and my intention to-night is to give you some of the results, so far as they bear upon irrigation; and having, as I said, no recognized instruments, I have designed some which seem to fulfil the following conditions—

(1.) That the grass and soil should each be as nearly as possible in its natural condition, and yet easily weighed as often as may be desired.

(2.) That the parts be as simple as possible, and easily reproduced for use in other places.

Two water-tight square dishes, exactly 2 feet on the side and 8 inches deep, were made of galvanized iron. Each, therefore, has a surface of 4 square feet from which evaporation goes on. Into one of them were put four sods carefully cut from the grass-plot, each being 1 foot square and 7 inches deep; the unavoidable spaces between these were filled up with water and soil. Into the other 7 inches of garden soil were put; each of them was then dropped into a hole in the grass-plot that exactly fitted it, but was only 7 inches deep. The grass and soil in the dishes are therefore level with that outside, and the edges of the dishes stand up 1 inch, to prevent surface water from running in when it rains. The weight is considerable-from 200 to 270 lbs., according to the amount of water present, and it is lifted by means of a lever; a very accurate spring balance comes between the evaporator and the lifting gear. It only takes a few minutes to weigh both accurately to 1-10th of a pound, and 1 lb. is equal to 0.048 of water on the whole surface.

I have but recently begun these experiments, and the wet weather has delayed the work; but, so far as I have gone, the

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