863 



session of the mind amidst great political changes, and politics no 

 sooner intrude than science is forced to retire. Still, under very un- 

 favourable circumstances, our neighbours, I think, have displayed a 

 greater amount of scientific energy than perhaps the most sanguine 

 could have ventured to anticipate. 



Without attempting to give an outline of the progress of foreign 

 science, which would occupy too much time, or pretending to assign 

 the order of merit to the achievements of the distinguished men to 

 whom that progress is due, it is impossible not to direct especial 

 attention to the remarkable researches of Weber on Electrodyna- 

 mical Measures ; a work where we have a happy combination of 

 applied mathematics, ingenious device, and judicious experiment, 

 resulting in important discoveries. His work commences with a de- 

 scription of a new and very ingenious instrument, which he calls an 

 Electrodynamometer. It consists of two coils of fine wire, the smaller 

 of which is suspended within the other by a bifilar suspension, so 

 that their centres coincide, and their axes are at right angles. He 

 calls the latter " the multiplier," the other " the bifilar (or rather sus- 

 pended) coil." They are so connected, that the current to be exa- 

 mined traversing the multiplier, passes by the suspending wires 

 through the suspended coil, which turns by their mutual action 

 through an angle whose tangent measures the intensity of their ac- 

 tion. The angle is measured as in the German magnetometers, by 

 observing with a telescope the reflexion of a scale placed at a con- 

 siderable distance in the mirror, carried by the bifilar coiL The 

 action between the coils is as the square of the intensity of the cur- 

 rent, while that exerted on the needle of a rheometer is simply as 

 the intensity. 



1st. He obtains absolute measures of the intensity by the use of a 

 small magnetometer, whose magnet is a steel mirror, which is placed 

 at a proper distance, and deflected by the action of the fixed coil, 

 "or multiplier," according to the principles laid down by Gauss, and 

 thus refers them to the earth's magnetism as a standard. 



2nd. He applies this instrument to verify Ampere's fundamental 

 law of electrodjmamics, and from it he computes the action of a single 

 ring on another, in three different relative positions of their centres, 

 the last being where they coincide, as in this instrument ; and finally, 

 he computes the mutual action of combinations of such rings. In 

 each the action is as the square of the intensity multiplied by a con- 

 stant, which is a function of the dimensions of the coils, and the 

 distance of their centres ; and he finds that the computed deviations 

 agree with the observed with an error never exceeding four seconds 

 of space. 



3rd. He applies the instrument to measure the intensity of an in- 

 duced current, thus : — Let the suspended coil be made to oscillate 

 round its vertical axis, while a constant current is passed through 

 the fixed coil; if the extremities of the former be connected, a cur- 

 rent is induced in it, which changes its direction twice in each os- 

 cillation, and which therefore shortens the arc of oscillation. Ob- 

 serve the decrements of this arc under the influence of the current. 



