the near and distant Sight of different Persons. 335 
belladonna, perfect vision of a near object was removed, as 
the dilatation advanced, from six inches (which was the 
nearest distance at which Dr. Cutting could distinctly see 
the image of the flame of a candle reflected from the bulb 
of a small thermometer) to seven inches in thirty minutes, 
and to three feet and a half in three quarters of an hour, 
My eldest son, who has a very extensive range of vision, has 
made a similar experiment on his right eye with a similar 
result. Previous to the application of the belladonna, he 
could bring the apparent lines on an optometer (like that 
improyed by Dr. Young from the inveution of Dr. Porter- 
field, and described in the Philosophical Transactions for 
the year 1800) to meet at four inches from the eye; and, 
by directing his attention to a more distant point, he could 
prevent them from meeting till they were seven inches 
from the eye, after which they continued apparently united 
the whole length of the optometer, which was twelve 
inches*. He could see the image of a candle reflected from 
the bulb of a small thermometer, five-sixteenths of an inch 
in diameter, at the distance of three inches and three quar- 
ters from the eye ; and he could also see the same image 
at the distance of two feet seven inches. The belladonna 
produced a conspicuous dilatation of the pupil in less than 
an hour; after which, on viewing the apparent lines on the 
optometer, he was unable to make them meet at a nearer 
distance than seven inches, or to gain a distinct image of 
the candle reflected by the bulb of the thermometer nearer 
than this distance; but he could discern it at two feet ten 
inches from the eye, which was three inches further than 
he was able to see it before the belladonna was applied. 
During the time of the experiment on the right eye, the 
left eye possessed its usual range of vision ; but the sight, 
when both eyes were open, was rather confused, in conse- 
qnence of the unequal foci of the two eyes; and it did not 
become clear until the pupil of the right eye recovered its 
usual power of contracting, which power was not acquired 
till the third day after the applicaticn of the belladonna. 
It is remarkable that a different effect is sometimes 
produced on a near-sighted eye by the application of the 
belladonna, from that which it has on an eye that enjoys a 
distant sight. Dr. Wells made an experiment of this kind 
* The two lines that are perceived on looking through the slits of an 
optometer, cross each other precisely in the point from whence the rays of 
light diverge in order to be brought to a focus on the retina. And their 
parent union before and after this point is occasioned by the unavoidable 
aleitens of the line drawn on the optometer. 
on 
