RECENT PROGRESS IN PHYSICS. 



403 



speaks in relation to this formula. Pie expresses himself stron^^ly 

 against it, so that one would get the notion that the entire conception 

 which Biot presented of the action of the condenser was not only faulty, 

 but lundaraentally wrong. liiess justly censures the misuse which has 

 been made of the formula in computing the condensing power of the 

 apparatus, and shows incontestably, by experiment, that such an a])pli- 

 cation is not admissible ; but in the introductory consideration he ex- 

 presses himself in a manner which would lead one to believe he desired 

 to prove far more against the formula than is in fact his purpose, and 

 from this cause it is somewhat difficult to understand his memoir. It 

 appears subsequently, however, that in his opposition to the formula 

 not so much is intended as would seem at first to be the case, and it 

 becomes clear to the reader after a while_, that he only censures the 

 misuse of the formula, which in the end rests upon the same notion 

 of the action of the condenser which he himself develo2)es. The dis- 

 cussion is in part a strife about words. 



We pass now to the experiments which Riess instituted to discover 

 and explain the mode of action of the condenser, and the circumstan- 

 ces which influence the capacity of the instrument for condensing. 



Two plane brass disks, 87.6 lines in diameter, ^i[ of a line thick, 

 with rounded edges^ were in the middle of one side provided with 

 cylindrical handles, 15 iines long and 11 lines thick. These handles 

 are perforated in their axes so that a conducting wire may be fastened 

 in them by means of a clamp screw. At right angles to their axes 

 they have a, cavity in which a glass rod, coated with shellac, somewhat 

 over eight inches long is cemented. These rods bearing the disks stand 

 vertically on a horizontal base as shown in fig. 43. 



The induced plate A or condenser can be laid on its back by means 



of a hinge. 

 The inducing 

 disk B, known 

 as the collect- 

 or is placedon a 

 slide so that it 

 can be brought 

 near to or re- 

 moved from A 

 at will, and the 

 distance mea- 

 sured accurately. 



The condenser A, when in use, was connected by a metallic wire 

 with the gas pipes of the house, as a discharging train. 



The collector B was connected by a metallic wire with one knob of 

 a spark micrometer, fig. 50, the other knob of which communicated 

 with the gas pipes of the house. 



_A being turned down, so that B stood alone, the latter was then elec- 

 trified by contact with the knob of a Leyden jar. The free electricity 

 distributed itself over the whole insulated system, that is, over the 

 plate B, and the knob of the spark micrometer connected witli it. 

 The striking distance of the electricity present was measured by the 



Fijr. 43. 



