Telegraphy, the most important technological prerequisite for modern meteorology, soon became his main interest. In June 1874, the year in which Edison invented his quadruplex telegraphy, la Cour invented a telegraphic device based on tuning forks. The idea was to permit a number of telegraphers to send messages on a single wire, each using his own frequency. By using the resonance phenomenon of tuning forks it was possible to split out the messages at the receiving end of the wire. He patented his invention in London on 2 September 1874, but in the United States Alexander Graham Bell, Elisha Gray and others had been working along similar lines, which resulted in protests against his American patent applications. Having too little money to pay lawyers, he gave up his claim in America, and this invention was credited to Elisha Gray. La Cour however maintained that Gray had been working on the invention of the telephone, and only had changed his invention at the instant la Cour's American application was published. La Cour later wrote in an autobiographical article that he felt some malicious pleasure when Graham Bell was awarded the telephone patent by applying only a few hours before Gray.