of Metals for reflecting ’felej copes. 349 
D Another piece of pafte-board, fixed by a pin to the 
piece of wood bb, on which it turns as on a center; fo 
that the great annular opening hh may be ihut up by 
the ring ff, or the aperture gg by the imperforate 
piece e in fuch manner that, in the firft inftance, the 
reflexion may be from the center, and in the latter, 
from the circumference, of the great Ipeculum. 
