CM*. 11.] DISSERTATION SECOND. 67 



one body could communicate electricity to another with- 

 out rubbing, being willing to try to what distance the elec- 

 trical virtue might be thus conveyed, employed, for the 

 purpose of forming the communication, a hempen rope, 

 which they extended to a considerable length, supporting 

 it from the sides, by threads which, in order to prevent 

 the dissipation of the electricity, they thought it proper to 

 make as slender as possible. They employed silk threads 

 with that view, and found the experiment to succeed. — 

 Thinking that it would succeed still better, if the supports 

 were made still more slender, they tried very fine metal- 

 lic wire, and were surprised to find, that the hempen rope, 

 thus supported, conveyed no electricity at all. It was, 

 therefore, as being silk, and not as being small, that the 

 threads had served to retain the electricity. This acci- 

 dent led to the great distinction of substances conducting, 

 and not conducting electricity. An extensive field of in- 

 quiry was thus opened, a fortunate accident having sup- 

 plied an instantia cruris, and enabled these experimenters 

 to distinguish between what was essential and what was 

 casual in the operation they had performed. The history 

 of electricity, especially in its early stages, abounds with 

 facts of this kind ; and no man, who would study the na- 

 ture of inductive science, and the rules for the interpre- 

 tation of nature, can employ himself better than in tracing 

 the progress of these discoveries. He will find abundant 

 reason to admire the ingenuity as well as the industry of 

 the inquirers, but he will often find accident come in very 

 opportunely to the assistance of both. The experiments 

 of Wheeler and Gray are described in the Transactions, 

 for 1729. 



