An essay on the investigation of the first principles of nature : Together with the application thereof to solve the phn̆omena of the physical system. Part I. Containing a new philosophical theory whereby first principles, with their material substances and effences are traced and exhibited; the limits of inertness assigned; the causes of elasticity and transparency discovered; the real mode of light's propagation determined; and various other phn̆omena clearly explained. The whole scientifically investigated and demonstrated by Felix O'gallagher.