This section is from the book "Scientific American Reference Book. A Manual for the Office, Household and Shop", by Albert A. Hopkins, A. Russell Bond. Also available from Amazon: Scientific American Reference Book.

1 dyne = that force which acting on 1 gramme for 1 second gives it a velocity of 1 centimeter per second (being absolute unit of force in the C.G.S. system, independent of local variations of gravity).

1 gram weight = at Paris, 980 dynes; at London, 981 dynes; at Glasgow, 982 dynes.

1 pound weight = 453.6 grams weight; = at Paris, 444,528 dynes; at London, 444,987 dynes.

1 pound per square inch = 0.0703 kilogram per square centimeter.

1 kilogram per square centimeter = 14.2 lbs. per square inch.

1 atmosphere = 30 in. of mercury = nearly 76 centimeters of mercury = nearly 15 lbs. per square inch = nearly 1,000,000 dynes per square centimeter.

The following will serve to illustrate the magnitude of some of these units:

10 ft. of pure copper wire 0.01 in. diameter is almost exactly equal to 1 ohm.

The current used in an ordinary incandescent lamp of 16 candle-power is about 0.6 ampere.

The electrical pressure of the terminals of the cell usually used for electric bells (Leclanche) is about 1.4 volt.

1 watt = about 44¼ foot-lbs. per minute.

746 watts = 1 horse-power.

1 kilowatt = about 1⅓ horse-power.

An easy way to convert watts into the equivalent horse-power is to mark off three places and add one-third: Thus,

What is the equivalent horse-power of 27,000 watts?

Set off three decimal places............... | 27.000 |

Add one-third............... | 9.000 |

And the horse-power required = | 36 |

Find the equivalent number of watts of 48 electrical horse-power?

Multiply the horse-power by 1,000, thus | |

48X1,000 = | 48,000 |

Subtract one-quarter, 48000 / 4 = | 12,000 |

And the required number of watts = | 36,000 |

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