490 WEBER OX THE >XEASUREMENT 



of natural philosophy has experienced, it would have long since 

 been disproved. The reason why neither the one nor the other 

 has been effected, depends upon the fact, that in the development 

 of electro-dynamics no such combination of observation with 

 theory has occurred as in that of the general theory of gravita- 

 tion. Ampere, who w as rather a theorist than an experimenter, 

 very ingeniously applied the most trivial experimental results to 

 his system, and refined this to such an extent, that the crude ob- 

 servations immediately concerned no longer appeared to have any 

 direct relation to it. Electi'o-dynamics, whether for their more 

 secure foundation and extension, or for their refutation, require a 

 more perfect method of observing ; and in the comparison of 

 theory with experiment, demand that we should be able accu- 

 rately to examine the more special points in question, so as to 

 provide a proper organ for what might be termed the spirit of 

 theory in the observations, without the development of which 

 no unfolding of its powers is possible. 



The following experiments will show that a more elaborate 

 method of making electro-dynamic observations is not only of 

 importance and consideration in proving the fundamental prin- 

 ciple of electro-dynamics, but also because it becomes the source 

 of new observations, which could not otherwise have been made. 



Description of the Instrument. 



The instrument about to be described is adapted for delicate 

 observations on, and measurements of, electro-dynamic forces ; 

 and its superiority over those formerly proposed by Ampere de- 

 pends essentially upon the following arrangement. 



The two galvanic conductors, the reciprocal action of which is 

 to be observed, consist of two thin copper wires coated with silk, 

 which, like multipliers, are coiled on the external part of the cavi- 

 ties of two cylindrical frames. One of these two coils incloses a 

 space which is of sufficient size to allow the other coil to be 

 placed within it and to have freedom of motion. 



When a galvanic current passes through the wires of both coils, 

 one of them exerts a rotatory action upon the other, which is of 

 the greatest intensity when the centres of both coils correspond, 

 and when the two planes to which the convolutions of the two 

 coils are parallel form a right angle with each other. The com- 

 mon diameter of both coils is the axis of rotation. This respective 

 position of the two coils constitutes the normal position, which 



