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production of oats—and thus again the wasteful use of water is emphasised.
It is generally true with all the ordinary crops grown in the Western States, that increasing the amount of water increases the yield up to a certain point, after which an increase in the water causes a decrease in the yield. Not all the crops are alike in this respect, however. Some crops, because of their nature-leaf surface, root system, etc.—find 10 inches of water about right for the season's growth. Other plants, because of their different natures, find 15 inches or 20, or 25 to 30 inches the best. Now, the farmer in an irrigated district should know the water requirements of the different plants that he grows as thoroughly as he knows the soil of his farm, his water right, or any other matters upon which his success as a farmer depends. Not all plants decrease in yield after a certain amount of water has been applied. Potatoes appear to be a crop, the yield of which increases continually if water is applied, up to the limit of the practical application of water. To illustrate :—in one set of experiments, 74 inches of water produced 160 bushels of potatoes; 15 inches 233 bushels; 30 inches 274 bushels; and 71 inches 315 bushels. This illustrates the necessity for the farmer to thoroughly understand the nature of the plants with which he is dealing.
It may be noted, in reviewing the yields of wheat, oats, and potatoes just considered, that the value of the first few inches of water applied is much greater than that of the later applications. For instance :- -5 inches of water produced about 33 bushels of wheat, or about 6.6 bushels per inch ; 15 inches of water produced about 40 bushels of wheat, or about 3.2 bushels per inch of water ; while 20 inches of water also produced 40 bushels of wheat, or only two bushels per inch. The value of the first 3 inches of water applied to wheat, therefore, is more that three times as much as the value of the last 5 inches, in a total depth of 20 inches. Similar results may be observed in the case of oats. Five inches of water produced 58 bushels, or 12 bushels per inch ; while 20 inches of water produced 86 bushels of oats, which is less than 5 bushels per inch of water. The difference is certainly very striking. Even in the case of potatoes, the yield of which increased steadily with the increase of irrigation water, the same fact holds. Seven and one-half inches of water produced 160 bushels, or about 22 bushels per inch ; while 30 inches of water produced 274 bushels, which is only about nine bushels per inch. Corn, alfalfa (lucerne), the various grasses, sugar beets, vegetables and all other crops show similar results ; namely, that the value of water is highest when it is used sparingly and carefully ; that the value of water is lowest when it is applied liberally and carelessly. With this generalisation in mind, note how these results may be viewed in their relation to the increase of the irrigated area.
According to the investigations of the Department of Agriculture, under the direction of Dr. Mead and his associates, 30 inches of water, or more, are used in the majority of places in the irrigated districts for the production of crops. Let us apply the varying value of water as just explained, to the economical, or rational, use of water. If the 30 acre-inches be spread over 6 acres of wheat, so that the whole area of 6 acres will be covered with water to a depth of 5 inches, each acre will yield 32} bushels of grain, or a total of
bushels. If the same amount of water be spread over 4 acres, that is, to a depth of 7 inches, the total yield of grain will be 165 bushels. Spread over 3 acres, to a depth of 10 inches, the same amount of water will yield 118 bushels. Spread over 2 acres, to a depth of 15 inches, the total yield will be 95 bushels, and spread over i acre, to a depth of 30 inches, the yield will be 42 bushels. It may thus be seen that, in the case of wheat the total amount of grain produced by 30 acre-inches of water may be increased from 42 bushels to 195 bushels by spreading the water over more or less ground. Certainly the nearly five-fold increase of grain thus made possible, will more than pay the farmer for the labour of handling six acres of land instead of one; and of higher importance is the fact that, by using the water rationally, the irrigated wheat area may be profitably increased four or five times without building another reservoir or canal.
These figures show how enormously a farmer can increase the area of land irrigated by a given quantity of water if he understands its scientific use. It is a subject worth studying, for on it depends to a large extent the agricultural prosperity of the country. Farm irrigation in South Africa has not received the attention it deserves, and I am looking forward to the time when the Transvaal will have Government experiment irrigation stations in various districts, under the superintendence of expert engineers and agriculturalists. They will be attended with the most valuable results.
By R. A. DAWBARN, M.I.C.E., M.I.E.E.
Just 600 years ago the British Parliament successfully petitioned the King to prohibit the use of coal in London, from which time its consumption gradually increased, but it is only within the lives of living men that the great demand for it has arisen for the generation of mechanical power, with which we are for the moment more directly concerned.
It is almost startling to recall the fact that only 70 years have elapsed since mail coaching was at its height-a zenith represented by 5.4 coaches throughout England, together unable to carry as many passengers as a single railway train to-day.
But it is perhaps still more remarkable that 20 years from the height of its prosperity sufficed to entirely supersede, the mail coach * and to establish the age of mechanical power.
Closely following the spread of railways came that rapid development of trade, demanding the use of power for almost every manufacturing industry, and with this demand a corresponding increase in the consumption of coal, until, at the present time, its output in England is fully 7 tons per annum per head of population.
But the consumption of coal in the Transvaal-chiefly for the generation of power-already exceeds 10 tons per head of white population, and anything which affects economy of fuel cannot fail to be of importance to South Africa.
Although the demands for power have been increasing with marvellous rapidity for half a century, singularly little advance has been made since the days of Watt in reducing the consumption of coal per unit of mechanical energy obtained from it, in spite of the realization of the fact that manufacturing countries must inevitably lose some all-important industries so as the cost of coal is seriously increased by the necessity for obtaining it from greater depths.
It is both difficult and expensive to provide means for accurately recording the average power consumed in factories in which many power-using tools are intermittently employed, except where electric motors are in use when accurate records of the energy absorbedhowever intermittent the load- can be obtained automatically, by the use of meters. It is therefore only since the establishment of electric distribution of energy that accurate costs of generating and distributing power have been systematically recorded.
On setting to work the earlier electric power stations, it was a surprise to most engineers to find how large the consumption of fuel was per unit delivered to the consumer. Consumptions of coal as high as 15 lbs. and more per unit sold, with non-condensing engines, were not uncommon, whilst 12 lbs. per unit sold was frequently experienced with condensing engines.
NOTE. – The first mail coach ran in 1784. The height of coaching was
reached in 1838. The last mail coach from London ceased running in 1856.
Even to-day there are few electric power stations in England consuming less than 6 lbs. of coal per unit sold. Of the 26 electric supply undertakings in the London Metropolitan area, supplying over 150,000,000 units a year, the average cost of coal in 1905 exceeded 0.5d. per unit sold. Assuming the average cost of coal to be 15/- per ton, this corresponds to an average consumption of 61 lbs. per unit sold. The average thermal value of the coal probably exceeds 13,500 B.Th.U. per Ib., on which basis 84,375 B.Th.U. are thus expended per electrical unit sold in London, whereas an electrical unit corresponds to 3,438 B.Th.U., consequently the overall thermal efficiency, that is to say, the proportion of the latent heat energy contained in the coal, which is recovered in the form of electric energy at consumers' premises throughout London, is practically 4 per cent.
By employing a small number of correspondingly larger engines of the most economical type, this efficiency ought, in the light of our present knowledge, to be greatly improved, but it is doubtful whether, with the most economical steam plant, and with the highest load factor obtainable under practical conditions, it is possible at the present time to generate and distribute electric energy 24 hours per day over a large area-involving extra high pressure mains and the consequent transforming losses—with a higher overall thermal efficiency than 8 per cent.
The following figures show approximately the distribution of losses, giving this result :
efficienes. Boiler efficiency
70%) Engine and dynamo 16 lbs. steam per unit
8% In view of the last-mentioned loss, it may at first sight be difficult to realize that a power-user, developing his own power direct by modern engines, could under any circumstances be supplied from a distant steam-power station at a lower price than his own cost, with profit to tie supplier, for the following reasons :
(a) The Power Distributor must (generally speaking)
generate his own power in similar manner, and can only obtain comparatively small advantage in the
higher efficiency of larger generating units. (b) The Power Distributor has to incur the additional
losses of converting his mechanical power as given off by the engines, into electrical power. He has also to incur losses in transmission, and must cover the consumers' losses in reconversion of the electrical energy into mechanical energy.
(c) The Power Distributor must incur heavy capital outlay
in dynamos and distributing mains, which the power
user, employing his own direct power plant, avoids. The author's object is to show, firstly, why it is possible under certain conditions to supply fairly large power-users by electrical distribution from a distance with advantage to both supplier and supplied, and, secondly, to point in general terms to the limitations of electric Power Distribution.
The advantage of the Power Distributor over the ordinary power-user employing his own plant, may be briefly described under the following headings :
(1) Large output.
1. LARGE OUTPUT.
It will be readily understood that as there are many charges which do not increase pro rata with the output—such, for instance, as management, attendance, and stores and repairs to a lesser extent—the larger the service from one generating station (within limits) the lower will be the cost per unit generated. Larger generating units are, moreover, more economical in fuel consumption than smaller ones, and require less attendance in proportion to the output.
2. DIVERSITY FACTOR. The diversity factor, however, plays a still more important part in establishing the advantage of electrical distribution of power. This may be best explained by a reference to a specific case :
The Natal Government Railways have an electric generating station supplying power to their railway workshops at Durban. There are no less than 406 motors in use, arranged to drive a corresponding number of tools of various kinds. No motor is any larger than is necessary to drive the particular machine to which it is attached. The total power required to serve the whole of these motors at once on full load would be 2000 K.W., but it is found in practice that the maximum power required to supply their aggregate requirements never exceeds 500 K.W. This is due to the fact that without design a number of motors are always at rest for one cause or another, whilst other motors are for the time being required to give less than the maximum power which the tools they drive may at times demand.
It follows that in such a case the capacity of the generating station can be reduced to about 25 per cent. of that which would be required to work every motor at full load at one time. This percentage is called the diversity factor. Although in this case the motors are all in one factory, the principle would be the same if every motor represented a separate factory. It is clear that the aggregate capital expended by the many proprietors in order to