paraffin oil and churn well together with a force-pump; the whole may then be mixed with 100 gallons of soft water. The oil readily separates from the water, and thus a perfect emulsion is not obtained: this difficulty has been solved by Mr Cousin’s paraffin naphthalene wash, which is patented, but can be made for private use. It is prepared as follows:—Soft soap, 6 ℔ dissolved in 1 quart of water; naphthalene, 10 oz. mixed with 112 pint of paraffin; the whole is mixed together. When required for use, 1 ℔ of the compound is dissolved in 5 to 10 gallons of warm water.
These two washes are essential to the well-being of every orchard in all climates. Not only can we now destroy larval and adult insects, but we can also attack them in the egg stage by the use of a caustic alkali wash during the winter; besides destroying the eggs of such pests as the Psyllidae, red spider, and some aphides, this also removes the vegetal encumbrances which shelter numerous other insect pests during the cold part of the year. Caustic alkali wash is prepared by dissolving 1 ℔ of crude potash and 1 ℔ of caustic soda in soft water, mixing the two solutions together, adding to them 34 ℔ of soft soap, and diluting with 10 gallons of soft water when required for use. Another approved insecticide for scale insects is resin wash, which acts in two ways: first, corroding the soft scales, and second, fixing the harder scales to stop the egress of the hexapod larvae. It is prepared as follows:—First crush 8 ℔ of resin in a sack, and then place the resin in warm water and boil in a cauldron until thoroughly dissolved; then melt 10 ℔ of caustic soda in enough warm water to keep it liquid, and mix with the dissolved resin; keep stirring until the mixture assumes a clear coffee-colour, and for ten minutes afterwards; then add enough warm water to bring the whole up to 25 gallons, and well stir. Bottle this off, and when required for use dilute with three times its bulk of warm soft water, and spray over the trees in the early spring just before the buds burst. For mites (Acari) sulphur is the essential ingredient of a spray. Liver of sulphur has been found to be the best form, especially when mixed with a paraffin emulsion. Bud mites (Phytoptidae, fig. 6) are of course not affected. Sulphur wash is made by adding to every 10 gallons of warm paraffin emulsion or paraffin-naphthalene-emulsion 7 oz. of liver of sulphur, and stirring until the sulphur is well mixed. This is applied as an ordinary spray. Nursery stock should always be treated, to kill scale, aphis and other pests which it may carry, by the gas treatment, particularly in the case of stock imported from a foreign climate. This treatment, both out of doors and under glass, is carried out as follows:—Cover the plants in bulk with a light gas-tight cloth, or put them in a special fumigating house, and then place 1 oz. of cyanide of potassium in lumps in a dish with water beneath the covering, and then pour 1 oz. of sulphuric acid over it (being careful not to inhale the poisonous fumes) for every 1000 cub. ft. of space beneath the cover. The gas generated, prussic acid, should be left to work for at least an hour before the stock is removed, when all forms of animal life will be destroyed.
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| Fig. 6.—Bud Mites (Phytoptidae). A, Currant Bud Mite (Phytoptus ribis); B, Nut Bud Mite (P. avellanae). |
For spraying, proper instruments must be used, by means of which the liquid is sent out over the plants in as fine a mist as possible. Numerous pumps and nozzles are now made by which this end is attained. Both horse and hand machines are employed, the former for hops and large orchards, the latter for bush fruit and gardens. In America, where trees in parks as well as orchards and gardens are treated, steam-power is sometimes used. Among the most important sprayers are the Strawson horse sprayers and the smaller Eclair and Notus knapsack pumps, carried on the back (fig. 7). The nozzles for “mistifying” the wash most in use are known as the Vermorel and Riley’s, which can be fitted to any length of tubing, so as to reach any height, and can be turned in any direction. The pumps in the machine keep the insecticide constantly mixed, and at the same time force the wash with great strength through the nozzle, and so to the exterior, as a fine mist; every part of the plant is thus affected.
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| Fig. 7.—Knapsack Sprayer for Liquid Insecticides. |
Beneficial Insects have also to be considered in economic entomology. They are of two kinds—(1) those that help to keep down an excess of other insects by acting either as parasites or by being insectivorous in habit; and (2) insects of economic value, such as the bee and silkworm. Amongst the most important friends to the farmer and gardener are the Hymenopterous families of ichneumon flies (Ichneumonidae and Braconidae); the Dipterous families Syrphidae and Tachinidae; the Coleopterous families Coccinellidae and Carabidae; and the Neuropterous Hemerobiidae, or lace-wing flies. Ichneumon flies lay their eggs either in the larvae or ova of other insects, and the parasites destroy their host. In this way the Hessian fly is doubtless kept in check in Europe, and the aphides meet with serious hindrance to their increase. If a number of plant-lice are examined, a few will be found looking like little pearls; these are the dried skins of those that have been killed by Ichneumonidae. The Syrphidae, or hover flies, are almost exclusively aphis-feeders in their larval stage. Tachina flies attack lepidopterous larvae. One of the most notable examples of the use of insect allies is the case of the Australian lady-bird, Vedalia cardinalis, which, in common with all lady-birds, feeds off Aphidae and Coccidae. The Icerya scale (Icerya purchasi) imported into America ruined the orange groves, but its enemy, the Vedalia, was also imported from Australia, and counteracted its abnormal increase with such great results that the crippled orange groves are now once more profitable. (F. V. T.)
ECONOMICS (from the Gr. οίκονοµική, sc. τέχνη, from οῖκος, a house, and νόµος, rule,—the “art of household management”), the general term, with its synonym “political economy,” for the science or study of wealth (welfare) and its production, applicable either to the individual, the family, the State, or in the widest sense, the world. How far the same considerations apply to all these spheres is one of the problems of economic thought in its widest sense. The term “economy” (q.v.) by itself, which should strictly mean the art of applying money (or wealth) wisely, has commonly come to mean the art of saving money, or spending as little as possible. In practice the study of “political” economy is mainly devoted to the sphere of the State; the welfare of the individual as a member of the State, and of the State in its relation to the world, being internal aspects of the prosperity of the State itself. Economics thus includes the discussion of all the numerous factors which make life profitable, whether to the nation or to the business, or to the individual man. It may be conceived either as an historical science (What principles have in fact paid?), or as an abstract science (What are the true principles which must pay, presupposing an ideal?). Economists at different times have studied both aspects, according to their lights, and influenced by historical conditions of philosophic thought. A text-book on economics necessarily deals, therefore, with the whole subject in a manner which need not here be followed, since separate articles are devoted in this work to the biographies of writers on economics, and also to the principal economic
