787 



was used in onr experiments^). Moreover, even if i( should be of 

 any importance, it would be eliminated by the above indicated 

 method of observation. The influence of the stationary coil upon the 

 higher conducting spring is probably not negligible, but it cannot 

 cause any errors, as neither in the calibration nor in the observations 

 is anything changed in this spring. 



It may also be mentioned that by the manner in vvhicii the con- 

 ductors are arranged, in connection with the order in which 

 readings are taken , any influence of the electro-magnet or the 

 rheostats upon the ammeters or of these upon each other, are elimi- 

 nated. These influences are moreover very small. 



Capillary action. At first we were rather uneasy about the capillary 

 action between the rods of the floats and the mercury surface, and 

 between the carriers of the experimental tube and the surface of 

 the liquid in the bath. The regular return of the carriers to the 

 same zero, proved that no disturbances from these causes occurred 

 in our experiments. We had always given great care to keeping the 

 mercury surface as pure as possible. 



Vibrations. Vibrations of the ground have a very injurious effect 

 upon the observations, as they are reproduced in the apparatus, 

 greatly magnified, and are likely to cause troublesome swinging of 

 the floating carrier. Vibrations in the microscope caused by the 

 vibration of the ground, which troubled us at first, could be avoided 

 by fixing the microscope more firmly. 



The carrier is moved by every change of the forces that act 

 upon it, which causes vertical oscillations of great amplitude. To 

 damp these, glass wings are attached to the floats, so that after 2 

 or 3 swings they come to rest. Finally, the vapour bubbles 

 that constantly rise in the bath, cause small vertical movements of 

 the carrier, which are more marked, the greater the density of the 

 liquid gas is. Against these vibrations the comparatively large inert 

 mass — about 200 grams — of the carrier combined with the 

 damping just mentioned, proved to be the best expedient. The 

 damping could as a matter of fact ha\'e been made much greater, 

 without any difficulty. But it was better not to go any further, as it 

 would have made the movements of the apparatus aperiodic, and 

 a few swings were very useful to bring the influence of the capil- 

 lary action upon the carriers each time to the same value. 



1) When the axis of the coil falls exactly in the plane of symmetry of the poles 

 and goes through the middle of the interferrum this force is strictly zero. 



