"A lens is a transparent body the two refracting surfaces of which are curved, or one of which is curved…
"A prism is a transparent body with two refraction surfaces that lie in intersecting planes. The angle…
"The inversion of the object is of little consequence when the instrument is employed for astronomical…
"The most simple refracting telescope consists of a tube, containing two convex lenses, the one having…
"Suppose a, to be a distinct object, from which pencils of rays flow from every point toward the object…
"Suppose the object o to be at such a distance, that the rays of light from it pass in parallel lines,…