Philosophical Transactions of the Royal Society is a scientific journal published by the Royal Society. In its earliest days, it was a private venture of the Royal Society's secretary. It was established in 1665, making it the second journal in the world exclusively devoted to science, after the Journal des sçavans, and therefore also the world's longest-running scientific journal. It became an official society publication in 1752. The use of the word philosophical in the title refers to natural philosophy, which was the equivalent of what would now be generally called science.