Page:EB1911 - Volume 28.djvu/486

Rh varied with yellow, the legs reddish. Its rostrum is unusually long, being five-sixths of the body length in the female, and slightly shorter in the male. The antennae are 7-jointed. The first three joints are much longer than thick; the four following are shorter, and the seventh not longer than thick. The larva is very common in hazel nuts and filberts. When the nuts are about half-grown, the female bores, with its rostrum, a minute hole in the still comparatively soft nut-shell, and deposits an egg within the nut. The egg is said to be pushed in by means of the long rostrum. As the nut grows the slight puncture becomes almost obliterated, so that it is unnoticed by all but the most observant eye. The larva is a thick white grub with a brownish head, bearing fleshy tubercles along its side. It feeds upon the substance of the nut. The nuts which are infested by this insect are usually the first to fall to the ground; the larva then bores a round hole through the nut shell, by means of its jaws, and creeps out. It hides itself in the ground during the winter, and in the spring it passes into the pupa stage, from which it emerges about August as the full-grown insect. A nearly allied form, Balaninus glandium, attacks both hazel nuts and acorns.

In an unobtrusive way weevils do immense harm to vegetation. This is effected not so much by their numbers and their powers of consumption, as amongst caterpillars, but by their habits of attacking the essential parts of a plant, and causing by their injuries the death of the plant affected. They destroy the young buds, shoots and fruits, and attack the young plants in their most delicate organs. Many of them devour seed, as the corn weevils, Calandra granaria and C. cryzae, and in this way vegetation is severely injured, and its spread seriously checked. Others cause much damage in forests, by boring under the bark and through the wood of trees, whilst some even burrow in the tissue of the leaves.

The Brenthidae, Anthribidae and Scolytidae are described in the article.

The Bruchidae are often called “weevils,” but they have no close affinity with the Rhynchophora, being nearly allied to the Chrysomelidae or leaf beetles. The antennae are straight, and inserted upon the head just in front of the eyes; they are 11-jointed, and serrated or toothed in the inside. Bruchus pisi causes considerable damage to pease; during the spring the beetle lays its eggs in the young pea, which is devoured by the larva which hatches out in it. (A. E. S.; G. H. C.)  WEGSCHEIDER, JULIUS AUGUST LUDWIG (1771-1849), German theologian, was born at Kübelingen, Brunswick, on the 17th of September 1771, studied theology at Helmstadt, was tutor in a Hamburg family 1795-1805, Repetent at Göttingen, professor of theology at Rinteln in Hesse (1806-1815), and at Halle from 1815. In 1830 he (with his colleague Wilhelm Gesenius) was threatened with deposition for teaching rationalism, and though he retained his office he lost his influence, which passed to F. A. Tholuck and Julius Müller. He died on the 27th of January 1849.

His chief works were Uber die von de neuesten Philosophie geforderte Trennung der Moral von der Religion (1804); Einleitung in das Evangelium Johannis (1806); and Institutiones Theologicae dogmaticae (1815), to which W. Steiger's Kritik des Rationalismus in Wegscheider's Dogmatik (1830) was a reply.  WEIGHING MACHINES. Mechanical devices for determining weights or comparing the masses of bodies may be classified as (a) equal-armed balances, (b) unequal-armed balances, (c) spring balances and (d) automatic machines. Equal-armed balances may be divided into (1) scale-beams or balances in which the scale-pans are below the beam; (2) counter machines and balances on the same principle, in which the scale-pans are above the beam. Unequal-armed balances may be divided into (1) balances consisting of a single steelyard; (2) balances formed

by combinations of unequal-armed levers and steelyards, such as platform machines, weighbridges, &c.

Scale-beams are the most accurate balances, and the most generally used. When constructed for purposes of extreme accuracy they will turn with the one-millionth part of the load weighed, though to ensure such a result the knife-edges and their bearings must be extremely hard (either hardened steel or agate) and worked up with great care. The beam must be provided with a small ball of metal which can be screwed up and down a stem on the top of the beam for the purpose of accurately adjusting the position of the centre of gravity, and there should be a small adjustable weight on a fine screw projecting horizontally from one end of the beam for the purpose of accurately balancing the arms.

The theory of the scale-beam is stated by Weisbach in his Mechanics of Machinery and Engineering, as follows:—In fig. 1 D is the fulcrum

of the balance, S the centre of gravity of the beam alone without the scales, chains or weights; A and B the points of suspension of the chains. If the length of the arms AC = BC = l, CD = a, SD = s, the angle of deviation of the balance from the horizontal =, the weight of the beam alone = G, the weight on one side = P, that on the other = P + Z, and lastly the weight of each scale with its appurtenances = Q then

From this it is inferred that the deviation, and therefore the sensitiveness, of the balance increases with the length of the beam, and decreases as the distances, a and s, increase; also, that a heavy balance is, ceteris paribus, less sensitive than a light one, and that the sensitiveness decreases continually the greater the weight put upon the scales. In order to increase the sensitiveness of a balance, the line AB joining the points of suspension and the centre of gravity of the balance must be brought nearer to each other. Finally, if a is made extremely small, so that practically $$\tan\phi = \frac{\text{Z} l}{\text{G} s}$$, the sensitiveness is independent of the amount weighed by the balance. Weisbach also shows that if Gy² is the moment of inertia of the beam, the time, t, of a vibration of the balance is

This shows that the time of a vibration increases as P, Q and l increase, and as a and s diminish. Therefore with equal weights a balance vibrates more slowly the more sensitive it is, and therefore weighing by a sensitive balance is a slower process than with a less sensitive one.

The conditions which must be fulfilled by a scale-beam in proper adjustment are:—(1) The beam must take up a horizontal position when the weights in the two scale-pans are equal, from nothing to the full weighing capacity of the machine. (2) The beam must take up a definite position of equilibrium for a given small difference of weight in the scale-pans. The sensitiveness, i.e. the angle of deviation of the beam from the horizontal after it has come to rest, due to a given small difference of weight in the scale-pans, should be such as is suited to the purposes for which the balance is intended. Bearing in mind that with ordinary trade balances there is always a possibility of the scale-pans and chains getting interchanged, these conditions require; (a) That the beam without the scale-pans and chains must be equally balanced and horizontal; (b) that the two scale-pans with their chains must be of equal weight; (c) that the arms of the beam must be exactly equal in length; i.e. the line joining the end knife edges must be exactly bisected by a line drawn perpendicular to it from the fulcrum knife-edge. By testing the beam with the scale-pans attached and equal weights in the pans, and noting carefully the position which it takes up; and then interchanging the scales-pans, &c., and again noting the position which the beam takes up, a correct inference can be drawn as to the causes of error; and if after slightly altering or adjusting the knife-edges and scale-pans in the direction indicated by the experiment, the operation is repeated, any required degree of accuracy may be obtained by successive approximations. The chief reason for testing balances with weights in the scale-pans rather than with the scale-pans empty, is that the balance might be unstable with the weights though stable without them. This is not an infrequent occurrence, and arises from the tendency on the part of manufacturers to make balances so extremely sensitive that they are on the verge of instability. In fig. 2 let ABCD be the beam of a scale-beam, Z the