SIR,
Perhaps the following method of assisting a
weak sight may not be commonly known. I translate it from La
Nouvelle Bigarure for February 1754.
“The author of this discovery was about sixty
years of age; he had almost entirely lost his sight, seeing
nothing but a kind of thick mist, with little black specks
which appeared to float in the air. He knew not any of his
friends, he could not even distinguish a man from a woman,
nor could he walk in the streets without being led. Glasses
were of no use to him; the best print, seen through the best
spectacles, seemed to him like a daubed paper. Wearied with
this melancholy state, he thought of the following
expedient.
“He procured some spectacles with very large
rings, and taking out the glasses substituted in each circle
a conic tube of black Spanish copper. Looking through the
large end of the cone he could read the smallest print
placed at its other extremity. These tubes were of different
lengths, and the openings at the end were also of different
sizes; the smaller the aperture the better could he
distinguish the smallest letters; the larger the aperture
the more words or lines it commanded, and consequently the
less occasion was there for moving the head and the hand in
reading. Sometimes he used one eye, sometimes the other,
alternately relieving each, for the rays of the two eyes
could not unite upon the same object when thus separated by
two opaque tubes. The thinner these tubes, the less
troublesome are they. They must be totally blackened within
so as to prevent all shining, and they should be made to
lengthen or contract, and enlarge or reduce the aperture at
pleasure.
“When he placed convex glasses in these
tubes, the letters indeed appeared larger, but not so clear
and distinct as through the empty tube: he also found the
tubes more convenient when not fixed in the spectacle-rings;
for when they hung loosely they could be raised or lowered
with the hand, and one or both might be used as occasion
required.” [1]
T. Y.
Bristol
, February 21.
