SIS 
PBRISCOPIC SPECTACLES. 
have misinterpreted the strict meaning of the author, I beg 
you will refer those who may wish to see the original, to the 
Moniteur of the 21st of September last. 
I remain. 
Sir, 
Your obliged and obedient Servant, 
W. H. WOLLASTON. 
Ntyv. 20th, 1S13. 
Observations on a new Kind of Spectacles, invented by Dr. 
Wollaston. 
Every one knows that those whose eyes are too convex, can- 
not see distant objects distinctly, because the pencils of rays of 
light intersect each other in the eye before they reach the re- 
tina. On the contrary, those whose eyes have too little con- 
vexity, as is generally the case in old persons, cannot see with 
distinctness those objects that are at a short distance, because 
the rays converge towards a point that is beyond the retina. ' 
The former defect is remedied by the use of concave glasses, 
which remove the focus of rays to a greater distance ; the 
latter is relieved by convex glasses, which have the effect of 
shortening the focus. 
But those who have recourse to common spectacles, cannot 
see with distinctness any objects which are not nearly in the 
direction of the axes of the glasses. Objects seen remote from 
the centres, are distorted and confused by reason of the obli- 
quity of the rays of the surfaces of the glass, which occasions 
a degree of irregular aberration. Hence, with such glasses, 
the view can embrace but a small number of objects at a time. 
The head must be moved in such a manner as to direct the axes 
of the glasses to each object in succession, with great incon- 
venience in very many instances. 
It is now some years since Dr. Wollaston proposed a remedy 
for this defect by a very simple invention. He remarked that, 
sine* 
