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:
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...............
And the horse-power required =
Multiply the horse-power by 1,000, thus
Subtract one-quarter, 48000 / 4 =
And the required number of watts =