on the Diameter of Optic Paid is* 507 
certainly run into great imperfections, we ought neverthelefs 
alfo to confider what dangers, 011 the other, we may incur by 
leffening them too much. 
As foon as convenient, I intend experimentally to purfue this 
fubjeCt, in order to obtain proper data for fubmitting this caufe 
of optical imperfeftion to theory ; at prefent my engagement 
with the work of a 40-feet refleCtor will hardly permit fo 
much leifure ; and till I (hall have repeated, extended, and 
varied thefe experimental inveftigations, I would wifli them to 
be looked upon as mere hints that may afford matter for future 
difquifitions to the theoretical optician. 
VoL. LXXVI. 
U u u 
