MEAD VILLE

"95

MEAT-PACKING

at every sound ; on the ground it allows close approach. The nest (on the ground) is cleverly hidden, grasses curved over it, and about the middle of May it contains from four to six brown-speckled white eggs. The meadowlark is distributed throughout North America, and migrates in April and late October, some birds remaining all winter. The bird is prized for its inspiriting note, the soft harmony of its coloring, its neighborliness and its usefulness in destroying insects and eating seeds of weeds.

Mead'ville, Pa., capital of Crawford County, on Venango River in northwestern Pennsylvania, 125 miles north of Pittsburg. It is on the Erie Railroad and in railroad connection with Pittsburg and Lake Erie. It is the seat of a number of educational institutions, schools, colleges, conservatories of music and half a dozen libraries. Here are Allegheny College, a Methodist institution, with 19 instructors and 352 students, and a Unitarian theological seminary. Its industries include manufactures of engines, boilers, leather-belting, oil-well supplies, wood-mantels, sashes and blinds. The city has good water-works, natural gas for fuel and lighting and electric-light plants. Population 12,780.

Meas'urement consists essentially in the comparison of one quantity with another. Thus the measurement of a length, which is one of the simplest of all measurements, consists in determining how many times greater or less the given length is than some other given length which we agree to take as a unit. In like manner an interval of time is measured by comparing it with the interval which we employ as a unit, namely, the mean solar day. Evidently, therefore, it is possible to measure a quantity without understanding much about that quantity. No intelligent measurement, however, can be made unless one understands just what quantities are necessary to define the quantity about to be measured. The position of a point in space is intelligently measured only when we know that three definite and independent co-ordinates are required to locate the point and have determined the numerical values of these three co-ordinates. To measure the kinetic energy of a body in translation we must know how many units of mass there are in the body and with how many units of speed it is moving. . Thus also we may accurately and definitely measure the acceleration of gravity at various points on the earth's surface, and yet not know the explanation of gravitation.

Practically all the quantities involved in physical science and engineering can be measured in terms of three quantities: a length, a time and a mass. The units of these three quantities are therefore called the fundamental units.

The standard of length, except in English and American commerce, is the meter; the

standard of time the mean solar day; and the standard of mass the kilogram. (See Earth, Kilogram and Meter.) Units are founded upon standards, but they often differ in size from standards and may be chosen of a size which, for any particular purpose, is most convenient. Thus, in physics the centimeter or hundredth of a meter is most frequently employed; and in astronomy the second (ī.tf °f a day) is frequently a very convenient unit of time, though often the year (or 365 days roughly speaking) is more convenient. • No physical measurements can be carried out with absolute accuracy. Every comparison is affected with error to some extent. Even the standard meter at Paris, which is correct by definition, may be changing its length owing to crystallization. The rate of rotation of the earth is probably diminishing (and hence the length of the mean solar day increasing) owing to tidal friction. Even if comparisons could be made with perfect accuracy, the final measurement would be affected with error. On the other hand, the precision of modern measurement almost surpasses belief. Michelson, for instance, has succeeded in making a comparison of the standard meter with a wave-length of cadmium light in which the error does not exceed about one part in 2,000,000. Two masses may be compared with even greater accuracy. See Everett's Units and Physical Constants.

Meat=Packing, an American industry which began with the salting of hogs for export from New England in the early years of American colonization, has now become one of the chief industries of the middle west. Its main centers are Chicago, Kansas City and Omaha, though it is carried on largely in other western cities. The industry includes the whole process of the disposal of carcasses of sheep, cattle and hogs killed for food. Thus meat-packing falls at once into two departments: the packing of fresh meat and that of cured meat. Both largely depend for success upon modern improvements in refrigeration. Fresh meat is simply frozen during some forty hours, and sent to market. But the bulk of the meat is canned or cured. The labor-saving devices in meat-packing have been brought to great perfection. The carcass is hoisted by the nose on an endless chain, and so passed through scalding-vats and automatically scraped. It is then disembowelled by machinery, beheaded, washed and trimmed, all these processes occupying but a few seconds. In meatpacking the bones are ground for manure or made into glue; and the hoofs, horns and hides are turned to account in many ways. The waste trimmings of the meat are made into sausages. It is obvious that such a process as meat-packing may be conducted carelessly and even in a manner dangerous to health. In 1891 a system of government inspection