... constructed; to the second we are indebted for the power of the lenses, and the blessings of sight, for the light acts upon the retina of the eye in the samemanner as on the lens of a camera. The latter ... plainlypercieved the effect, in the gradual darkening of various parts of the view, which was the old stone fort in the rear of the school garden, with the trees, fence, &c. I then became convinced of the ... the picture, arising from the blending of the rays. The diameter and focal length of a lens must depend in a great measure on the distance of the object, and alsoon the superficies of the plate or paper...