Page:The American Cyclopædia (1879) Volume XVI.djvu/557

 menclature of these is in much confusion. The one first introduced as W. rosea, now called by some D. Japonica, has given origin to many varieties; it grows about 5 ft. high, with nu- merous erect stems, ovate-lanceolate, serrate leaves, and a profusion of rosy or nearly white flowers, an inch or more long. What is called D. (or Weigela) amabilis is much taller, with recurving branches and larger leaves. Both of these have given varieties, and there has been much crossing, so that the list of named sorts is long ; they differ in the color and abundance of their flowers, and there are two with varie- gated foliage. Among the desirable varieties are hortensis nivea, with pure white flowers and blooming a long time ; Isoline, with white flowers having a yellow blotch in the throat, and changing to blush; and Desbomi, with flowers of the deepest rose color, and so abun- dant as to make the stem a continuous gar- land. Others are described in the catalogues, and new varieties are frequently added. These plants are perfectly hardy, and multiplied by cuttings from the recent shoots taken just as they begin to harden. WEIGHING MACHINES, contrivances for ascer- taining the measure of gravity (or weight) of different bodies. The simplest and most accu- rate form of weighing machine is the common balance, a lever of the first kind with equal arms. This may be made sensitive to within less than ^Vtf of a grain. (See BALANCE, vol. ii., p. 234.) Weighing machines in which a small weight may be made to counterpoise a large one may be in the form of the steelyard, which is a lever of the first kind with the two arms in varying proportions, one arm being sometimes 300 times as long as the other, so that a two-pound weight would be capable of balancing and therefore measuring the weight of a body of 600 Ibs. Compound levers are usually employed for heavy goods, arranged in the form of what are called platform scales. They are used in the weighlocks of canals for weighing boats (see CANAL, vol. iii., p. 681), and in market places for weighing car and dray loads. The arrangement is shown in the arti- cle MECHANICS, vol. xi., p. 327. Machines of this kind are constructed in works of great ex- tent at St. Johnsbury, Vt., in New York, and various other places, and of all sizes, from those adapted for the use of families, grocers, and druggists, that may be placed upon a table, up to those of a capacity of 200 to 500 tons. The only other kind of what may strictly be called weighing machines is the spring balance. (See BALANCE.) Of this there are various forms, in which a spiral spring by coiling or uncoil- ing measures the force of gravity of the body weighed by means of a revolving index. When the spring is made of well tempered steel, the spring balance answers for most purposes where great accuracy is not required ; but the balance with equal arms is the only one which can be used in weighing very small quantities. A hydrometer may be used to weigh solid bod- WEIGHTS AND MEASURES 537 ies and estimate their specific gravities, as well as the specific gravities of liquids ; but it is not considered in the ordinary sense as a weighing machine. (See HYDROMETER.) WEIGHTS AND MEASURES, means of deter- mining by comparison, and expressing, in the former instance, the mass or quantity of mat- ter of ponderable bodies, as shown by the effect of gravity upon them, and in the latter, the magnitudes of bodies, or of the various forms under which we regard and estimate space. The different species of quantity, of measure, and of unit may be classed as follows : 1, weights;. 2, solidities or volumes (in body, or space) ; 3, surfaces ; 4, angles ; 5, lines ; 6, times; 7, values (money, the artificial mea- sure); 8, intensities or forces (expressed in weights or lengths). Quantity is always that which can be measured. But in order to find and express the measure of a quantity, we must first either find in nature or assume ar- bitrarily some fixed magnitude or value of the given kind, by comparison with which the relative amounts of the various examples of that kind of quantity are to be ascertained. This fixed magnitude or value is the unit of measure of the given kind of quantity, or in a given one among many systems of measuring it. Whether found in nature or arbitrarily chosen, the unit itself is always incapable of measurement, and is, in se, an unknown mag- nitude ; so that all measures are comparative or relative only. Since four right angles just fill the entire space about any point in a plane, and so correspond to the entire circumference of a circle, the right angle becomes a natural measure, or invariable natural unit; and the value of any definite part of this or of the circle is equally fixed. The early geometers accordingly divided the circle or its circum- ference into 360 equal parts, one of these parts, 1, becoming the unit of circular or of angular measure; and this measurement is still re- tained. In estimating time, two natural units present themselves, the day and the year. (See CALENDAR, and YEAR.) For the subject of measures of value, see COIN, MONEY, and the articles on the various denominations of money. For measures of intensity of various natural agencies, see ELECTROMETER, LIGHT, THERMOMETER, &c. See also the titles of the ordinary measures. The forms of measure to be considered in this article are: weight; measures of length, giving linear or long mea- sures ; of surface or area, giving square or su- perficial measures ; and of solidity or volume. Absolutely invariable standards of weight and measure have never yet been, and in the nature of the materials to be dealt with cannot be, attained ; while to secure and reproduce mea- sures of given sorts, the results of which shall be correct and uniform to within the least practicable degree of variability, is a problem upon which a vast amount of scientific research, ingenuity, and labor has been expended. The balance, or scales, in a rude form, are known