296 ROUGH WAYS MADE SMOOTH. 



of an intense heat along the aerial track where the spark Is 

 seen. 



In the case of electricity generated by means of a gal- 

 vanic battery, we do not note the same phenomena unless 

 the battery is a strong one. We have in such a battery a 

 steady source of electricity, but unless the battery is power- 

 ful, the electricity is of low intensity, and not competent to 

 produce the most striking phenomena of frictional elec- 

 tricity. For instance, voltaic electricity, as used in tele- 

 graphic communication, is far weaker than that obtained 

 from even a small electrical machine. What is called the 

 positive extremity of the battery neither gives a spark, nor 

 attracts light bodies. The same is true of the other, or 

 negative extremity. The difference of the condition of 

 these extremities can only be ascertained by delicate tests 

 the deflections of the needle, in fact, by which telegraphic 

 communications are made, may in reality be regarded as 

 the indications of a very delicate electroscope. 



But when the strength of a galvanic battery is sufficiently 

 great, or, in other words, when the total amount of chemical 

 action brought into play to generate electricity is sufficient, 

 we obtain voltaic eltctricity Lot only surpassing in intensity 

 what can be obtained from electrical machines, but capable 

 of producing spark after spark in a succession so exceed- 

 ingly rapid that the light is to all intents and purposes con- 

 tinuous. 



Without considering the details of the construction of a 

 galvanic battery, which would occupy more space than can 

 here be spared, and even with fullest explanation would 

 scarcely be intelligible (except to those already familiar with 

 the subject), unless illustrations unsuited to these pages 

 were employed, let us consider what we have in the case oi 

 every powerful galvanic battery, on whatever system ar- 

 ranged. We have a series of simple batteries, each con- 

 sisting of two plates of different metal placed in dilute acid. 

 Whereas, in the case of a simple battery, however, the two 

 different metals are connected together by wires to let the 



