13 



Magnetic susceptibility (*) is the ratio of intensity of magnetization 

 produced and the intensity of the magnetic field producing it. The dimensional 

 formula is [M^ry/A/'L^ry-*] or [p]. 



Mutual inductance of two circuits is the electromotive force produced in 

 one per unit rate of variation of the current in the other. The dimensional 

 formula is the same as for self -inductance. 



Peltier effect, coefficient of, is measured by the ratio of the quantity of 

 heat and quantity of electricity. The dimensional formula is [M LrT" 1 / 'M h IJ /T } ] 

 or [M i L"T~ 2 fj}\, the same as for electromotive force. 



Quantity of electricity is the product of the current and time. The dimen- 

 sional formula is [frPL*/*'*]. 



Resistance of a conductor is the ratio of the difference of potential be- 

 tween its ends and the constant current flowing. The dimensional formula is 



[M*L» , ry/jif»L*rv , i or [LT^n]. 



Resistivity is the reciprocal of conductivity as just defined. The dimen- 

 sional formula is [L 2 T~ l fji\. 



Self-inductance is for any circuit the electromotive force produced in it by 

 unit rate of variation of the current through it. The dimensional formula is 

 the product of the formulae for electromotive force and time divided by that 

 for current or [M*L»ry xr4-M»L»rV*l or [L/*]. 



Thermoelectric power is measured by the ratio of electromotive force and 

 temperature. The dimensional formula is [M i L i T'-/x i &' 1 ]. 



Exs. — Find the factor required to convert intensity of magnetic field from ft-grain-min 

 units to cgs units. The formula is [m>l~'r 1 n~>] ; m — 0.0648, / = 30.48, / = 60, and m = 1 ; 

 the factor is 0.0648^ X 30.48-3, or 0.046108. 



How many cgs units of magnetic moment make one ft-grain-sec unit of the same quan- 

 tity? The formula is lm l l *">*] ; m = 0.0648. 1 = 30.48, t '= 1, and fi=l; the number 

 is 0.0648* X 30.48?, or 1305.6. 



If the intensity of magnetization of a steel bar is 700 in cgs units, what will it be in 

 mm-mg-sec units? The formula is [m J / } rV J l ; m = 1000, / = 10, t = 1, /J. — 1; the in- 

 tensity is 700 X 1000* X 10*, or 70000. 



Find the factor required to convert current from cgs units to earth-quadrant-10 u 

 gram-sec units. The formula is [«i*/*rV J ] ; m — 10 11 , / = 10 9 , fi—l; the factor is 

 10VX10-J, or 10. 



Find the factor required to convert resistance expressed in cgs units into the same ex- 

 pressed in earth-quadrant-10 -11 gram-sec units. The formula is 1/rVl ; / = 10~°, t — 1, 

 M = 1 ; the factor is 10 _o . 



TABLE 3.— FUNDAMENTAL STANDARDS 



Part 1. — Selection of fundamental quantities 



The choice of the nature of the fundamental quantities already made does 

 not sufficiently define the system for measurements. Some definite unit or 

 arbitrarily chosen standard must next be taken for each of the fundamental 

 quantities. This fundamental standard should have the qualities of perma- 

 nence, reproducibility, and availability and be suitable for accurate measures. 

 Once chosen and made it is called the primary standard and is generally kept 

 at some central bureau — for instance, the International Bureau of Weights 

 and Measures at Sevres, France. A primary standard may also be chosen and 

 made for derived units (e.g., the new absolute (1948) ohm standard), when 

 it is simply a standard closely representing the unit and accepted for practical 



SMITHSONIAN PHYSICAL TABLES 



