The outlines of physics: an elementary text-book . Fig. 2. also their relations to one another, should be committed tomemory. The following approximate relations to the units of othersystems, which can also readily be memorized, are veryuseful: Two and a half centimeters make an inch (nearly).A meter is about 39^^ kilometer is about | of a gram is about 15^^ kilogram is about 2^% pounds. A liter is about If pints (iinperial) or rather more than 1 quart (1-056)U. S. standard. INTRODUCTION 6. The unit of time is the second. It is ^5^-5^ of themean time from noon to noon.
The outlines of physics: an elementary text-book . Fig. 2. also their relations to one another, should be committed tomemory. The following approximate relations to the units of othersystems, which can also readily be memorized, are veryuseful: Two and a half centimeters make an inch (nearly).A meter is about 39^^ kilometer is about | of a gram is about 15^^ kilogram is about 2^% pounds. A liter is about If pints (iinperial) or rather more than 1 quart (1-056)U. S. standard. INTRODUCTION 6. The unit of time is the second. It is ^5^-5^ of themean time from noon to noon. The instrument by whichtime is measured is the clock, which is a machine for keep-ing a pendulum in motion, and for counting its pendulum is of such a length, usually, that it makesone vibration per second (see further, Chapters V and VI). A simple apparatus by means of which short intervals oftime are indicated to the ear, but not counted, is the. Fig. 3. metronome (Fig. 3). This consists of a short pendulumdriven by clockwork. The rate of the pendulum is adjust-able by means of the sliding weight w, between 40 vibra-tions and 208 vibrations a minute. At each beat it ticksloudly. The. metronome is used chiefly by students ofmusic, but it is likewise a valuable apparatus in the physi-cal laboratory. For illustrations of its application, seeArts. 38, 40, 43, 44, etc. 6 THE OUTLINES OF PHYSICS 7. Measurements of length are always made by the use,directly or indirectly, of a divided scale, usually a copy,more or less exact, of a part or the whole or some multipleof the standard meter. For measurements of precision the divisions of the scaleare ruled with a diamond upon metal or glass, giving linestoo fine for use with the naked eye. In such cases observa-tions are made with a microscope. 8. The Estimation of Tenths. — In comparing any lineardistance with a scale, the boundaries rarely (one may saynever) coincide precisely with thcu31924031253697
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