Masterpieces of Science 



lona, the covering of subaqueous wires by resin, 

 which is both impenetrable by water and a non- 

 conductor of electricity. Insulators, indeed, of 

 one kind and another, were common enough, but 

 each of them was defective in some quality in- 

 dispensable for success. Neither glass nor 

 porcelain is flexible, and therefore to lay a con- 

 tinuous line of one or the other was out of the 

 question. Resin and pitch were even more faulty, 

 because extremely brittle and friable. What of 

 such fibres as hemp or silk, if saturated with tar 

 or some other good non-conductor ? For very 

 short distances under still water they served 

 fairly well, but any exposure to a rocky beach 

 with its chafing action, any rub by a passing 

 anchor, was fatal to them. What the copper 

 wire needed was a covering impervious to water, 

 unchangeable in composition by time, tough of 

 texture, and non-conducting in the highest degree. 

 Fortunately all these properties are united 

 in gutta-percha : they exist in nothing else known 

 to art. Gutta-percha is the hardened juice of a 

 large tree (Isonandra gutta) common in the 

 Malay Archipelago; it is tough and strong, easily 

 moulded when moderately heated. In com- 

 parison with copper it is but one 60,000,000,000,- 

 ooo,ooo,oooth as conductive. As without gutta- 

 percha there could be no ocean telegraphy, it is 

 worth while recalling how it came within the 

 purview of the electrical engineer. 



In 1843 J os e d' Almeida, a Portuguese engi- 

 neer, presented to the Royal Asiatic Society, 

 38 



