APPENDIX. 



437 



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

 equal to 10" 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, 144521 grams in mass, of a 

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

 = 1/9 X io- u E. S. U. 



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

 B. A. ohm = 0.9865 1 international ohms. 

 Siemens' ohm = 0.94080 international ohms. 

 PENTANE CANDLE. Photometric standard. See page 260. 

 PI = TT = ratio of the circumference of a circle to the diameter = 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 = i8oA = 57.29578 57 i/ 45" = 206265". 

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

 THERM = small calorie = (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. R). 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 8 E. M. U. = 1/300 E. S. U. See page 197. 

 VOLT-AMPERE. Equivalent to Watt/Power factor. 



WATT. The unit of electrical power = io 7 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 = amperes 2 X ohms = volts'/ohms (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.) */2. 

 YEAR. See page 414. 



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

 Sidereal " =365 "6 9 9-314 



Ordinary " =365 " 5 " 4 " 46 + 

 Tropical ; same as the ordinary year. 



