104 Prof. W. C. Rontgen on the Change in the Double 
removed. I will mention here only a few of* the observations 
leading to this conclusion, which will serve to show how 
carefully it is necessary to proceed and how the results may 
be confirmed. 
Two opposite fields of the sphere, e. g. 2 and 5, were com- 
pletely covered with tin-foil, but so that the two pieces of tin- 
foil did not touch each other ; then the sphere was so placed 
upon the insulated brass cylinder that the pressure took place 
in the direction of an axis of no piezoelectricity joining the 
bounding line between fields 1 and 6 with that between fields 
3 and 4. The brass rod by which the pressure is exerted was 
in connexion with the electroscope. If then all the fields 
remained insulated, the electroscope showed no electricity 
upon change of pressure ; but if field 2 were connected with 
the ground, positive electricity was observed, produced by the 
induction of field 5, which was strongly charged with positive 
electricity. The electroscope showed a negative charge if 
field 5 alone were connected with the ground. 
If, when fields 2 and 5 were connected with the ground, 
field 1 was also put to earth by being touched with the finger, 
I obtained a feeble negative deflection of the gold leaf due to 
induction by the negative electricity produced on field 6. 
In order to show that in the position of the sphere indicated 
it was actually the whole halves of the sphere, and not alone 
the fields 2 and 5, which became electrified, these fields were 
connected with the earth, and fields 1, 3, 4, and 5 in order 
were tested with the electrode connected to the electroscope. 
They were found to be, upon increase of pressure, feebly but 
decidedly electrified, positively or negatively as the case 
might be. 
If the sphere were placed upon the brass disk connected 
with the earth, with the covered portions above and below, 
and if pressure were exerted upon it in the direction of an 
axis of maximum piezoelectricity, positive electricity was 
obtained upon the whole sphere if the positive field ."> was 
uppermost, but, on the other hand, negative electricity if the 
negative field 2 was uppermost. In these cases the inductive 
action of the piezoelectricity produced above overpowered 
the feeble action of the opposite electricity present upon the 
lower half of the sphere. Xormal conditions resulted when 
the lower field was also insulated. In this position of the 
sphere it could be shown that electricity was present upon 
the whole whole upper and lower halves, and not only at the 
points of pressure. 
If the coated fields were connected with the earth, the 
other fields showed qualitatively the same distribution of 
electricity as already described. 
