GALVANIC .ELEMENT GALVANIC CIRCUIT. 653 



of the condenser plates should be perfectly dry. In lifting the upper 

 plate it must be held quite parallel to the lower plate, for if one 

 portion of the edge is raised while another still remains in contact 

 with the lower plate, recombination of the two electricities is apt to 

 take place through the thin layer of varnish at the place of contact. 

 The knob of the electroscope must, in all cases when electricity is 

 to be communicated to the instrument from a condenser, be touched 

 by the unvarnished portion of the plate ; the upper plate, therefore, 

 after it is raised, must be turned with the handle downwards, and 

 the knob touched by it while it is held in this position. For 

 moistening the blotting paper a solution is made of a few grains of 

 common salt in a few drops of water. The paper should be held 

 with the forceps while it is moistened and placed upon the strip of 

 zinc, so as to avoid making the fingers wet, and by them wetting 

 the sealing-wax handles. 



An arrangement for producing electricity, consisting 

 of two metals and a conducting liquid, constitutes a 

 galvanic element or a simple galvanic circuit. The two 

 metals are called the poles of the element, the copper 

 being the positive pole, the zinc forming the negative 

 pole. Besides metals, some other substances carbon, 

 for example may be used in a similar manner for .pro- 

 ducing electricity. 



When two galvanic elements are arranged in such a 

 manner that the zinc of one element is in conducting 

 connection with the copper of the other, twice as great 

 an effect is produced as by a single element, for although 

 the two connected metals no longer give electrical indi- 

 cations, the copper of the first element is found to be 

 twice as strongly positive, and the zinc of the second 

 twice as strongly negative, as before, when there was 

 only one element. A suitable combination of a series 

 of galvanic elements is called a galvanic battery. 

 Fig. 336 represents a battery of six elements. The 

 copper of the first element, and the zinc of the last, are 



