The Abbeville banner. [volume] (Abbeville, S.C.) 1847-1869, 1857-08-13
THE USE OF sPECTACLEs.

| An article Ill the North British Rcvicw
evidently from the pen of Sir David Brew
stcr, contains some interesting remarks OF
the use Of spectaclcs. Persons who hav,
enjoyed distinct and comfortable vision il
carly life, it is remarked, nro the most likely
to appreciate the benefit to bc derived from
glasses. Between tho ages of thirty and
forty, they begin to experience change in
| sight. This is the commencement of lone
slshtcdncss, growing out Of an incipient af.
lection of the crystalline lens, beginning at
the edge and proceeding toward tho centre.
During the progress Of this alteration, much
inconvenience is experienced, ;s no spccta-
Giles seem to be scrviccable in giving correct
vision. Happily, however, two or three
months ends this difficulty, and rs soon us
the alteration is complete distinct and com
Portable vision is at once obtained by the
Use Of well selected glasses of q convex fix.
turc. Durin. this transition state, il is I'M
portant that the eye should be subjected to
no severe strain, and great regard should
bc paid TO the general health.
Tho material Of spectacle lenses should
be glass of a very low dispersivc power, or
better still, OF rock crystal. They should be
double convex, the proper rldii Of the inner
and outer surfaces being in glass as to /,
and III rock crystal rs If 10 l. They should
be rs thin us practicable. To correct a
common error in the manufacture of lenses
by Which the distance between the centres
OF the lenses is made precisely equal 10 the
distance between tho centres Of the pupils
OF the eyes. the following rule is given:
Draw on paper III isoscecs triangle, the
two sides Of Which arc equal to the distance
OF each pupil from the point to be Sc II dis
tlnctly; while the third side or base is equal
to tho distance between the pupils when the
eyes view that point. Then set of OIL each
side of the triangle, from each end Of the
base, the distance Of tic centre Of the lenses
or their frames from the pupil, and the dis
tancc OF these points will Le the distance of
the centres of the lenses required"
The long,sightcd person will generally,
Tor ten or twelve years, require glasses only
for reading or work done by hands, but as
lltc advances other speetaclcs will be needed
for objects at greater distances, and it will
bc of great advantage TO have two or three
pair of different focal distances. It is yc-
ry incorrect notion that it is prudent to
avoid the use Of artificial helps to the eye
as long as possible.
The human eye is TOO delicate slruc-
turc to bear continued strain without injury,
and the true rule is, to commence the use
OF glasses us soon rs we can see better with
than without them. For special purposes,
as reading 4 very fine print or examining
maps, hand reading glass two and hall
inches i'll diameter, to be used i'll conjunc-
ton with spectacle, and never without them,
is strongly recommended. The practice
frequently indulged in of using IN eye glass
whose frame is grasped by the muscles Of
the eyebrow, cannot be to strongly condcn.
ned. Whenever it is found necessary to
moderate the quantity Of light admitted to
the eyes by means Of colored glasses, they
never SHOULD be blue, which arc more mis-
chievous than useful. Green glass is better,
but the best Of all is colorless glass of i'm
perfect transparency known by the name Of
"neutral tin: glass;" by which the intensity
Of the transmitted light can be diminished
to any desired degrec.-Boston Journal.