The simple hand magnifier are often employed by microscopist in the preliminary examinations of objects.
A very good form in lens was proposed by Dr. Wollaston, and called by him the Periscopic lens: which consisted of two hemispherical lenses cemented together by their plane faces, having a stop between them to limit the aperture. A similar […]

To assist us in gaining a clearer notion to the mode in which a single lens serve to magnify minute objects, it is necessary to take a passing glance at the ordinary phenomena of vision. The human eye is so constituted, that it can only have distinct vision when the rays falling upon it care […]