NOTE 
On the Attempts to grind Lenses and Mirrors by Machinery, 
and to give them a Parabolic Form. 
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We find very early notices of attempts to apply machinery to grind- 
ing the object-glasses of telescopes. In the first number of the Philosophical 
Transactions (1665), mention is made of glasses produced this way by 
Campani in Italy. Campani at Bologna, and Devini at Rome, were about 
that time disputing on the relative merits of the lenses which they produced, 
and the preference was generally given to the former. A machine employed 
by him is said to be still preserved in the apartments of the Institute at 
Bologna, and was found there by M. Fougeroux; it is not mentioned 
what peculiarities it had, but it was something of the nature of the common 
lathe, and probably, like almost all that have been since invented, was used 
only to assist, and not to supersede the work of the hand. Hooke in his 
Micrographia, published 1665, describes a machine for performing the 
whole work. In this, the glass and the tool turn each about its axis, these 
axes being inclined at a small angle to each other, and consequently, the 
motions of each particle of the glass and the tool being oblique with respect 
to each other. This method, however, appears liable to the objection which 
we shall find to apply to almost all those which have been proposed without 
experimental proof of their sufficiency. Namely, that each particle of the 
glass is ground by a surface whose motion, relatively to it, is, at similar points 
of the revolution, always the same, so that the inequalities of friction would 
act in the same manner in each successive revolution; and these cycles 
of action would probably cause the friction to affect the parts differently, 
according to their distance from the axis. It was also objected to by 
