APPENDIX. 



437 



OHM. Unit of electric, 1 resistance. The international ohm is based upon the ohm 

 equal to lo' units of resistance of the C. G. S. system of electromagnetic units, and 

 "is represented by the resistance offered to an unvarying electric current by a 

 column of mercury, at the temperature of melting ice, 14.4521 grams in mass, of a 

 constant cross section and of the length of 106.3 centimeters." = 10" E M U 

 = 1/9 X 10-"^ 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. 

 PENTANE CANDLE. Photometric standard. See page 260. 

 PI ::z TT ;= ratio of the circumference of a circle to the diameter rr; 3. 141 59265359. 

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



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

 RADIAN = 180° A = 57.29578° = 57° 1/ 45" =206265". 

 SECOHM. A unit of self-induction^ i second X i ohm. 

 THERM = small calorie =1 (obsolete). 



THERMAL UNIT, BRITISH = the quantity of heat required to warm one pound of 

 water at its temperature of maximum density one degree Fahrenheit =: 252 gram- 

 calories. 

 VOLT. The unit of electromotive force (E. M. F.). The international volt is "the 

 electromotive force that, steadily applied to a conductor whose resistance is one 

 international ohm, will produce a current of one international ampere. The value 

 of the E. M. F. of the Weston Normal cell is taken as 1.0183 international volts at 

 20° C. = io« E. M. U. = 1/300 E. S. U. See page 197. 

 VOLT-AMPERE. Equivalent to Watt/Power factor. 



WATT. The unit of electrical power =; 10'' units of power in the C. G. S. system. It is 

 represented sufficiently well for practical use by the work done at the rate of one 

 Joule per second. 

 Watts = volts X amperes = amperf'-^ X ohms = voltsyohms (direct current or alter- 

 nating current with no phase difference). 

 For conversion factors see page 197. 

 Watts X seconds = Joules. 

 WEBER. A name formerly given ,to the coulomb. 



WORK in ergs = dynes X cm. Kinetic energy in ergs = grams X (cm./sec.) V2. 

 YEAR. See_ page 414. 



Anomalistic year = 365 days, 6 hours, 13 minutes, 48 seconds. 

 Sidereal " =365 " 6 " 9 " 9.314 



Ordinary " =365 " 5 /' 48 " 46+ " 



Tropical " same as the ordinary year. 



