. Electrical world. of Capacities.—McClelland.—An application of radio-active substances for a simple and accurate method for comparingcapabilities. The method is suitable for the determination of capaci-ties of any magnitude down to a few micro-microfarads or even method is based on the fact that the ionization current that canbe obtained by the use of a radioactive substance like uranium isextremely constant and can be made so small that the time taken tocharge a condenser by it can be accurately measured. This smallconstant current is used first to charge one conde
. Electrical world. of Capacities.—McClelland.—An application of radio-active substances for a simple and accurate method for comparingcapabilities. The method is suitable for the determination of capaci-ties of any magnitude down to a few micro-microfarads or even method is based on the fact that the ionization current that canbe obtained by the use of a radioactive substance like uranium isextremely constant and can be made so small that the time taken tocharge a condenser by it can be accurately measured. This smallconstant current is used first to charge one condenser to a givenpotential; and then a second condenser is charged to the same poten-tial, and the time taken in the two cases observed, so that we get theratio of two capacities by simply observing two intervals of is not necessary to have a supply of radium; uranium is evenbetter in some respects and uranium is to be found in every labor-atory. In Fig. 4 A and B are two insulated plates, one of which, B,. FIG. 4.—COMPARISON OF CAPACITIES. can be joined to one terminal of a battery of small storage cells,the other terminal of which is to earth. The battery may consistof 100 or more small test-tube cells, so that B can be kept at 200volts or higher. A few grams of uranium nitrate are spread on asheet of paper and placed on the plate A. The radiation from theuranium ionizes the air between A and B; and so A gradually risesin potential if insulated, supposing B to be positive. The ionizationcurrent thus obtained between two plates increases at first as thepotential differences between the plates increases. But when thispotential difference is made sufficiently great, the current attains amaximum and does not further increase, for further increase ofpotential difference between the plates. If, then, B is kept at asufficiently high potential, small changes in this potential, due to thepotential of the battery falling, will produce no effect: and again,in making an obser
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectelectri, bookyear1883
