Volta's first formal paper on electricity, bearing the title _De Vi Attractiva Ignis Electrici_, was published in 1769, when he was twenty-four years of age. His second paper, _Novus Ac Simplicissimus, Electricorum Tentaminum Apparatus_--New and Very Simple. Apparatus for Electrical Tests, shows that Volta was getting beyond the stage of theorizing about electricity into the experimental work, which was to form the foundation of his contributions to electrical science. It is not surprising, then, that when he was just past thirty, in 1775, he was able to announce to Priestley his invention of the electrophorus. Priestley is usually thought of as one of the founders of modern chemistry, but he was known to his own generation, especially at this time, as the writer of a very interesting and complete history of electricity. It is characteristic of Volta's careful ways, that the reason for his letter to Priestley was in order to obtain information from him as to what extent this invention, which Volta knew, as far as he was concerned, to be original with himself, was novel in the domain of electrical advance.[20] With the intense interest in his work that we have noted, it is not surprising to find Volta's investigations proving fruitful. His active inventive genius stood him in good stead in enabling him to demonstrate principles by working instruments. The electrophorus is but one of the instruments that show the very practical character of the man. He was especially taken with the idea of securing some method of measuring electricity. Among other things, he invented the condensing electroscope, in which, instead of the ribbons of gold leaf now employed, he used straws. With this instrument he was able to demonstrate the presence of minute quantities of electricity developed under circumstances in which ordinarily the occurrence of any such phenomena would be unsuspected. These two instruments, the electroscope and the electrophorus, lifted the department of electricity out of the realm of theory into that of accurate scientific demonstration, and made the electrical departments of the physical laboratories of the time much more interesting and important than they had been before.