SCIENCE IN THE INDUSTRIAL WORLD 



frequent occasions when fog or storm would interfere 

 with these telegraphs. 



Such telegraphing by signals, however, was only pos- 

 sible during clear weather, and as it frequently hap- 

 pened that most important messages were delayed many 

 days by unfavorable atmospheric conditions, attempts 

 were probably made from the earliest times to discover 

 some means of telegraphy whereby messages could be 

 sent with certainty in daylight or in darkness regardless 

 of the weather. 



FUNDAMENTAL DISCOVERIES 



The discovery of electricity, or rather a discovery by 

 Stephen Gray that electricity could be conducted prac- 

 tically unlimited distances by means of wires or threads, 

 made possible the modern telegraph. But several 

 discoveries as to the properties and possibilities of elec- 

 tricity were necessary, after Gray's initial discovery, 

 before telegraphy in practical form was possible. The 

 principles involved in these discoveries, such as the dis- 

 covery of the principle of galvanic electricity, by Gal- 

 vani, the close association between electricity and magne- 

 tism by Oersted, and the principle of electromagnetic 

 induction by Michael Faraday, have been fully described 

 in a preceding volume of this series dealing with the 

 history of scientific principles, and need only be referred 

 to here in direct connection with certain discoveries; 

 and for full descriptions of them the reader is referred to 

 earlier volumes of the series. 



Although Stephen Gray made the discovery that 



