The elements of natural philosophy : copiously illustrated by familiar experiments and containing descriptions of instruments, with directions for using : designed for the use of schools and academies (1856)
Sprague, A. W. (Alfred White), 1821-1891 · Boston : Phillips, Sampson & Company · leaf 324
black spot, so that a distinct percep-tion of its form may be produced. The objects visible at adistance will then be found to become indistinct. But if theattention be directed more to the distant objects, so as to ob-tain a distinct perception of them, the perception of the blackspot on the glass… … vertical heights, in proportion to their distances from the eye.As each subtends the same visual angle, their apparent heightswill be equal. Thus, a small gnat near the eye may cover thesame angle and appear equal in size to an eagle at a distance. 301. TJie eye stipplies no direct perception of…
Physics
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