346 



APPENDIX. 



FOOT-POUND. The work which will raise one pound one foot high. 



For conversion factors see page 237. 

 FOOT-POUNDALS. The English unit of work = foot-pounds/g. 



For conversion factors see page 237. 

 g. The acceleration produced by gravity. 



GAUSS. A unit of intensity of magnetic field = I E. M. U. = $ X IQ- 10 E. S. U. 

 GRAM. See page 6. 



GRAM-CENTIMETER. The gravitation unit of work = g. ergs. 

 GRAM-MOLECULE, = x grams where x = molecular weight of substance. 

 GRAVITATION CONSTANT = G in formula G ^ = 666.07 X io~ 10 cm. 3 /gr. sec. 2 



For further conversion factors see page 237. 



HEAT OF THE ELECTRIC CURRENT generated in a metallic circuit without self- 

 induction is proportional to the quantity of electricity which has passed in coulombs 

 multiplied by the fall of potential in volts, or is equal to (coulombs X volts) / 4.181 in 

 small calories. 



The heat in small or gram-calories per second = (amperes 2 X ohms)/4.i8i = volts 2 / 



(ohms X 4.181) = (volts X amperes)/ 4.181 = watts/4. 181. 

 YT. Absolute zero of heat = -273.13 C, -459.6 Fahrei 



HEAT. Absolute zero of heat = -273.13 C, -459.6 Fahrenheit, -218.5 Reaumur. 



HEFNER UNIT. Photometric standard; see page 178. 



HENRY. Unit of induction. It is "the induction in a circuit when the electromotive force 

 induced in this circuit is one international volt, while the inducing current varies at 

 the rate of one ampere per second." = io 9 E. M. U. = $ X IQ- 11 E. S. U. 



HORSE-POWER. The practical unit of power = 33,000 pounds raised one foot per min- 

 ute. = 55oft. pds. per sec. = o. 746 kilowatt = 746 watts. 



JOULE. Unit of work = io 7 ergs. 



Joules = (volts 2 X seconds) / ohms = watts X seconds = amperes 2 X ohms X sec. 

 For conversion factors see page 237. 



JOULE'S EQUIVALENT. The mechanical equivalent of heat = 4.185 X io 7 ergs. See 



KILODYNE. 1000 dynes. About I gram. 



LITER. See page 6. 



LUMEN. Unit of flux of light-candles divided by solid angles. 



MEGABAR. Unit of pressure = 0.987 atmospheres. 



MEGADYNE. One million dynes. About one kilogram. 



METER. See page 6. 



METER CANDLE. The intensity lumination due to standard candle distant one meter. 



MHO. The unit of electrical conductivity. It is the reciprocal of the ohm. 



MICRO. A prefix indicating the millionth part. 



MICROFARAD. One millionth of a farad, the ordinary measure of electrostatic capacity* 



MICRON. (/*) = one millionth of a meter. 



MIL. One thousandth of an inch. 



MILE. See pages 5, 6. 



MILE, NAUTICAL or GEOGRAPHICAL = 6080.204 feet. 



MILLI-. A prefix denoting the thousandth part. 



MONTH. The anomalistic month = time of revolution of the moon from one perigee to 



another = 27.55460 days. 

 The nodical month = draconitic month = time of revolution from a node to the same node 



again = 27.21222 days. 



The sidereal month = the time of revolution referred to the stars = 27.32166 days (mean 

 value), but varies by about three hours on account of the eccentricity of the orbit and 

 "perturbations." 



The synodic month = the revolution from one new moon to another = 29.5306 days 

 (mean value) = the ordinary month. It varies by about 13 hours. 



OHM. Unit of electrical resistance. The international ohm is based upon the ohm equal 

 to io 9 units of resistance of the C. G. S. system of electromagnetic units, and "is repre- 

 sented by the resistance offered to an unvarying electric current by a column of mer- 

 cury, at the temperature of melting ice, 14.4521 grams in mass, of a constant cross 

 section and of the length of 106.3 centimeters." = io 9 E. M. U. = I X io~ u E. S. U- 

 International ohm = 1.01367 B. A. ohms = 1.06292 Siemens' ohms. 

 B. A. ohm = 0.98651 international ohms. 

 Siemens' ohm = 0.94080 international ohms. See page 272. 



PENTANE CANDLE. Photometric standard. See page 178. 



PI = Tf = ratio of the circumference of a circle to the diameter = 3.14159265359. 



POUNDAL. The British unit of force. The force which will in one second impart a veloc- 

 ity of one foot per second to a mass of one pound. 



RADIAN = i8o/7r = 57.29578 = 57 17' 45" = 206625". 



SECOHM. A unit of self-induction = I second X I ohm. 



