reservoir capacity will suffice to supplement the supply during all seasons. The action in all hydraulic motors is obtained by the fall of a volume of water from a higher to a lower level, the function of such motors consists in intercepting a portion of the moving force of the water during its fall. The merits of the different motors depend on the proportion the intercepted force bears to the whole force of the water; this percentage of the entire force is known as the effective force. The usual measure of effect is that of the horse-power as co-efficient of work equal to the raising of thirty-three thousand pounds one foot high per minute. It is not a difficult problem to determine what quantity of water descending through a known space will be equal to a horse power; the total fall of a stream of water for power is the height of the surface of the water in the reservoir above the level of the tail race; the force of the water or the effect which it produces is the product of the weight of the water multiplied by the total fall. A cubic foot of water, at a temperature of 55° Farenheit, weighs 62.5 lbs. As a portion only of the absolute power of the water can be intercepted and utilised by the different motors in use, hence a deduction must be made from the arbitrary to the efficient in accordance with the efficient construction of the motor. The varieties of motors more general in use are the Undershot, the Breast, the Overshot Wheel, and the Turbine. In this calculation the arbitrary force is assumed to be I.00. In accordance with this calculation the Undershot wheel will give an effective power of 0.350; the Breast wheel will give 0.540; the Overshot wheel 0.610, and the best class of Turbine 0.820. The conservation of water, particularly in hilly districts, has a source of power, and hence is susceptible of much more extensive application than is generally supposed. A rainfall of

By

two inches per annum on one square mile of surface furnishes a discharge of nine cubic feet per minute; a rainfall of thirty inches places within easy reach a source of power which which we are apt to overlook. I look upon water power as one of the most valuable a landowner can possess. Minerals become exhausted and there is no reproduction, but water retains its value for all time. In level districts the difficulty to contend with is backwater, and this is more particularly the case with the water-wheel. The outlet becomes blocked, the tail water accumulates, acting as a counterpoise, and completely stops the wheel. To obviate this difficulty in the case of an undershot wheel we had the floats hung on pivots. Immediately each float reached the lowest point and began to ascend, the weight of the tail water pressing on the opposite side caused it to swing back, thus freeing it from the back pressure. this means the wheel could be worked with the tail water nearly up to the level of the head, the speed was reduced, and consequently the effective power, The water wheel was formerly largely used in Derbyshire In the Southern division of the county, the slack gradients of the rivers seldom afforded a head of more than eight feet. Cotton doubling and other industries necessitating the employment of a large number of hands were common. During the winter months it was no uncommon occurrence for the mills to stand still for days and even for a whole week at a stretch; the hands were thrown idle, and the whole business disorganised owing to the laxity of the owners of water power at the time of the passing of the Factory Acts, which does not admit of any lost time being worked up; hence, in some cases the tenants of water mills not unfairly held this as sufficient grounds on which

as a motor.

In many

to base a claim for a reduction of rent. cases the difficulty has been met by the substitution of turbines; these have generally given the greatest satisfaction. Within the last eight years turbines of an aggregate of four hundred horse-power have taken the place of water-wheels on the estates with which I am connected; they can be constructed to run in tail water without loss of efficiency; their small size, moderate or high rate of speed, and regularity of motion, places the turbine at the head of every other motor with which we are acquainted. Like every other class of machines these vary largely in construction and effective power. Turbines are divided into two classes, those in which the water acts entirely by impulse, and those in which the water acts partly by pressure and partly by impulse. The principal kinds of pressure turbines are the inward flow, outward flow, and parallel flow; in the former the water enters the wheel on the outer and leaves it on the inner circumference. In what is known as the Fourneyrow the water enters the wheel on the inner and leaves it on the outer circumference. The Jonval, or parallel flow turbine, the water enters and leaves in a parallel direction with the axis. In what is known as the American turbine the water enters the wheel on the outside, passes inwards, and discharges downwards. The Gerard, or action turbine, differs in principle from others; here the water issues from the guide ports with the full velocity due to the head pressure, and thus acts entirely by impulse glides along the concave sides of the buckets without coming into contact with the convex sides. One great advantage this machine has over most others is that it retains its efficiency when working as low as quarter gate, or even less. This is a great advantage where the water supply is a varying quantity. The

adjustment is effected by a slide which opens or closes one port on each side, so that any number of ports may be open to suit the water supply or power requisite. This slide, which will also entirely shut off the water, is worked by a hand wheel attached to an index pillar, which shows the number of ports open. This turbine, which possesses many advantages, has this one drawback, that, under ordinary conditions, the bottom of the wheel must just be clear of the tail water in order to insure a free discharge. To obviate this it is sometimes necessary to lessen the head. The manufacturer, Mr. W. Gunther, of Oldham, can, to some extent, obviate this difficulty. We look upon electricity as the coming power. If we are right in our surmise the use of turbines must extend for the working of dynamos. Another improvement likely to hasten the use of water power is the reduced cost of constructing weirs for this purpose. Concrete is superseding the old-fashioned stone erections, which the first flood frequently carried away. Now the entire weir, when finished, is composed of a single block, which, if skilfully constructed, will stand for ages.

GILBERT MURRAY.

CHAPTER LXX.

LAND SURVEYING AND LEVELLING.

BY ROBERT RICH,

Diploma-Member and Prizeman of the Royal Agricultural Society, Member of the Royal Agricultural College, Fellow and Examiner of the Surveyors' Institution.

WITHIN the very narrow limits allowed in this book for these two branches of the same subject, it is impossible to do more than very briefly to summarise the main principles on which the practices of Surveying and Levelling are based.

The craft of measuring land was undoubtedly exercised some centuries before the Christian era. Indeed, so soon as proprietary rights in land were recognised, some means of estimating and stating the comparative areas of appropriated tracts must have existed. There is real reason to believe that the exact art of measuring land had its genesis in Egypt, when it became necessary to re-mark boundaries which had been set up by taxcollectors and husbandmen in its fertile valley, but which had been effaced by the annual overflowing of the mighty Nile. Euclid, whose name has struck terror into countless generations of schoolboys, more than that of any other historic "tyrant," was in reality but a gentle teacher of surveying. He was the first exact and scientific surveyor of land, and he flourished about the year 300 B.C. Out of his practice in re-marking the obliterated boundaries of land, arose the celebrated