78 GAUSS AND WEBER ON TERRESTRIAL MAGNETISM. 



We will add a few remarks on one or tAvo circumstances. 



" In speaking of the units to be employed in the measurements, 

 mention was made only of a unit of distance and a unit of 

 weight. But it should not be overlooked, that a certain weight, 

 (a gramme, for instance,) does not mean, in this case, the quantity 

 of ponderable matter which bears this name, and which is every- 

 where the same, — ^but the force which this quantity of matter 

 exerts at the place of observation, under the influence of gravita- 

 tion. It is well known that the force of gravity is not absolutely 

 the same at different places ; and if we chose the force of a gramme 

 for our unit of weight, the intensity of the earth's magnetism 

 would not be accurately measured by one standard at various 

 places. The accuiacy with which these measurements may now 

 be made is such that this difference must not be neglected. The 

 most simple way of meeting this difficulty is to reduce the force 

 of gravity itself to an absolute quantity, by adopting as its mea- 

 sure the double height of descent in the unit of time, (for in- 

 stance, a second,) and by expressing the force by the product of 

 the mass into the number which measm-es the force of gravity. 

 In this manner other numbers* are obtained, both for the force 

 of the magnetic needle employed, and for that of the earth's 

 magnetism ; which numbers are based on three units, i. e., a 

 unit of distance, a unit of time, and a unit of mass — instead of 

 resting on the two units before spoken of." 



In calculating the numbers M and T according to equations 



(V.) and (VI.) 



1 /Cmtangj; y_ 1 / 2C 

 ^ TV 2 tV ii^ang./ 



the value ascribed to the constant C was 



9 

 in which tt represented the known number 3'14159...; g, 

 double the space of descent in the unit of time ; K, the moment 

 of inertia of the vibrating bar. The new numbers are obtained 

 from the same equations, by ascribing to C the value 

 C = 7r2 K. 



« They are to tin previous numbers iu the proportion of the square root of 

 the number which measures the force of gravity to unity. 



