The unit of _solid measure_ is the _stere_, from the Greek, and is the cube of a metre, or, in other words, a solid mass one metre long, one metre broad, and one metre high. The unit of _liquid measure_ is the _litre_, from the Greek, and is the cube of the tenth part of the metre, which is the _decimetre_; or, in other words, it is a vessel where by interior measurement each side and the bottom are square _decimetres_. The unit of _weight_ is the _gram_, also derived from the Greek, and is the one-thousandth part of the weight of a cubic litre of distilled water at its greatest density,--this being just above the freezing-point. Such are main elements of the metric system. But each of these has multiples and subdivisions. It is multiplied decimally upward, and divided decimally downward. The multiples are from the Greek. Thus, _deca_, ten, _hecto_, hundred, _kilo_, thousand, and _myria_, ten thousand, prefixed to _metre_, signify ten metres, one hundred metres, one thousand metres, and ten thousand metres. The subdivisions are from the Latin. Thus, _deci_, _centi_, _milli_, prefixed to _metre_, signify one tenth, one hundredth, and one thousandth of a metre. All this appears in the following table. Metric Denominations and Equivalents in Denominations Values. in use. Myriametre, 10,000 metres, 6.2137 miles. Kilometre, 1,000 metres, .62137 mile, or 3,280 feet and 10 inches. Hectometre, 100 metres, 328 feet and 1 inch. Decametre, 10 metres, 393.7 inches. METRE, 1 metre, 39.37 inches. Decimetre, ⅒ of a metre, 3.937 inches. Centimetre, ¹⁄₁₀₀ of a metre, .3937 inch. Millimetre, ¹⁄₁₀₀₀ of a metre, .0394 inch. These same prefixes may be applied in ascending and descending scales to the are, the litre, and the gram. Thus, for example, we have in the ascending scale, _deca_gram, _hecto_gram, _kilo_gram, and _myria_gram,--and in the descending scale, _deci_gram, _centi_gram, _milli_gram. In this brief space you behold the whole metric system of weights and measures. What a contrast to the anterior confusion! A boy at school can master the metric system in an afternoon. Months, if not years, are required to store away the perplexities, incongruities, and inconsistencies of the existing weights and measures, and then memory must often fail in reproducing them. The mystery of compound arithmetic is essential in the calculations they require. All this is done away by the decimal progression, so that the first four rules of arithmetic are ample for the pupil.