so 
SCIENTIFIC NEWS, 
TO CORRESPONDENTS , tgc. 
Circumstances have prevented the insertion of Dr. Armstrong 1 s 
communication later than was intended. 
I shall pay attention to the remark with which M. D. has 
favoured me in his postcript. It does not appear to me, that 
any practical advantage would result from plano-covex or plano- 
concave spectacles, in preference to other lenses of like foci ; 
neither do I apprehend that such lenses ought to le charged at 
an higher price, supposing the workmanship and materials to he 
ike same . 
L. 0. C.’s Reply to Mr. Kerby came too late for the present 
number, hut will appear in the Supplement. . 
The Engraver, by an accident, has spoiled the plate of Mr. 
Telford's bridge, which could not be re-engraved in time. It 
will appear in the next number. 
The Supplement to VoU XXXI V will be published in the course 
of the month. 
