CHAP. III. PEECAUTIONS. 33 



Thirdly. Cleanliness is of the utmost importance. 

 Many experiments have ended in fallacious results 

 from the mere want of attention to this circumstance. 

 The platinum electrodes should be perfectly clean, 

 especially the extremities ; they should be well rubbed 

 with a dry clean cloth, after and previous to the 

 formation of each circuit during the experiment, 

 and occasionally exposed to the heat of a clear fire. 

 The secondary current, due to the polarized state of 

 the platinum electrodes, must not be forgotten ; to 

 remedy this, the ends of the electrodes should be 

 dipped into water, and their free extremities brought 

 into contact so as to form a circuit, and then 

 cleaned. No acids or alkalies should be employed, 

 or allowed to come into contact with the hands, or 

 fingers, or the towels, unless for some purpose in 

 the experiments : the hands and fingers should be 

 perfectly clean, and no dirty towels used. 



There is one observation to be made in reference 

 to the employment of the galvanometer. It may be 

 supposed that a great difficulty is experienced in 

 obtaining any result with this instrument, and that 

 it is absolutely necessary to employ a delicate instru- 

 ment for this purpose; nothing is more fallacious. 

 There is no difficulty in getting an effect upon the 

 needle in these experiments, but the contrary; the 

 diflficulty is not to get an effect. In saying this, 

 however, it is not to be supposed that no satisfactory 

 results are to be obtained ; I only wish to observe, 

 that it is not the mere motion of the needle and its 



