Transcribe
Translate
Sewell Van Alstine diary, 1863-1864
Theory of near sightedness
More information
digital collection
archival collection guide
transcription tips
105 Theory of near sightedness If the humors of the eye are to convex, parallel rays, & such pencils as diverge from pts at any considerable distance, are collected before they reach the retina; & objects to be seen distinctly must be brought near the eye; this inconvenience may be remedied by a concave glass, whose focal length is adjusted to such a degree of divergency as the eye requires; Contra: When the humors of the eye are to flat, The rays which diverge from a pt. near the eye, converge to a pt Behind the retina; which imperfection may be remedied by a convex lens, whos focal length &c: as above In the choice of glasses for long, or short sighted persons, care should be taken to select such as have the least refracting power that will answer the purpose, for, the eye has a tendency to retain that conformation to which it is accustomed; by the use of improper glasses, its imperfections may be increased; The extent of country drained by the Miss. R.& its tributaries 1,210,000 Square miles, the average annual depth of water falling on its surface is estimated at 52 inches, it is estimated that 1/12 of that is discharged by the Miss R, 11/12 evaporates
Saving...
prev
next
105 Theory of near sightedness If the humors of the eye are to convex, parallel rays, & such pencils as diverge from pts at any considerable distance, are collected before they reach the retina; & objects to be seen distinctly must be brought near the eye; this inconvenience may be remedied by a concave glass, whose focal length is adjusted to such a degree of divergency as the eye requires; Contra: When the humors of the eye are to flat, The rays which diverge from a pt. near the eye, converge to a pt Behind the retina; which imperfection may be remedied by a convex lens, whos focal length &c: as above In the choice of glasses for long, or short sighted persons, care should be taken to select such as have the least refracting power that will answer the purpose, for, the eye has a tendency to retain that conformation to which it is accustomed; by the use of improper glasses, its imperfections may be increased; The extent of country drained by the Miss. R.& its tributaries 1,210,000 Square miles, the average annual depth of water falling on its surface is estimated at 52 inches, it is estimated that 1/12 of that is discharged by the Miss R, 11/12 evaporates
Civil War Diaries and Letters
sidebar
