32 ELECTRICAL STRUCTURE AND 



THE ACORN. 



A beautiful simplicity characterises this seed, and one 

 might well believe that from it was borrowed the principle 

 of the modern incandescent electric lamp-holder. 



As will be seen from the example given in Fig. 30, the 

 cups in which the acorns are seated are joined up, as it 

 were, in series, while the negative terminal is in the form 

 of a circle, a, at the bottom of the cup ; the seed carrying 

 upon its posterior part a circular protuberance, b, which 

 seats exactly upon the contact a. 



Fig. 30. ACORNS. 



Electrically considered, the acorn is similar in con- 

 struction to the horse-chestnut seed. There are three 

 insulating membranes, and the secretion of the seed sub- 

 stance is also distinctly acid. It should have a fairly long 

 life owing to the excellence of its absolute insulation, to the 

 ample provision of moisture, and to the fact that it can 

 take in positive charge from the air through the point at the 

 apex of the seed. 



In common with other seeds, such as the Barcelona 

 nut, etc., there are sometimes two seeds within the shell. 



