KARL FRIEDRICH GAUSS 243 



and indeed away from the earth may have any value 

 whatsoever. In the absolute system, the unit of force is de- 

 rived by means of Newton's second law of motion from the 

 units of mass and acceleration (which latter follows from 

 the units of length and time). This unit of force is very 

 small; it is about equal to the weight of a milligram, and later 

 received the name 'dyne.' By means of the unit of force 

 and Coulomb's law it is easy to deduce a unit of magnetic 

 pole-strength. But it would be equally easy to deduce from 

 the same law as applied to electricity a unit of electric quan- 

 tity. It is here that the two branches of the absolute system 

 of units divide: the electro-magnetic units correspond to the 

 first choice, that of Gauss, the electro-static, to the second, 

 which was also later followed up by Weber. 



The fact that Gauss preferred to take the magnetic pole 

 rather than the quantity of electricity, was mainly due to his 

 desire to reduce the intensity of the earth's magnetism, as 

 regards its geographical distribution, to a single and easily 

 maintained unit of measurement, after comparative measure- 

 ments had already been made by means of the oscillations of 

 magnetic needles, particularly by Humboldt; and in a 

 balloon, for the first time, by Gay-Lussac. 



In this the main necessity was the settlement of an abso- 

 lute unit of magnetic intensity (strength of the magnetic 

 field, as we also say since Faraday's time), and of a method of 

 carrying out trustworthy measurements in this unit. Both of 

 these goals were reached by Gauss in a manner which is 

 still of full value to-day. Unit magnetic field is defined by 

 the fact that a unit pole is acted upon by unit force (one 

 dyne) when placed in it; a multiplication of the pole strength 

 and of that of the field both caused (according to Coulomb's 

 law) a proportionate multiplication of the force. The 

 method of measurement refers to the horizontal component 

 of the field strength (in the sense of the parallelogram of 

 forces), which is completely sufficient when the inclination 



