110 Dr. H.Hudson’s Remarks on M. Melloni’s and 
forming at its base the hypothenuse of the right-angled isosceles 
triangle I F E; in this second brass screen there is a circular 
opening (P), about 23 inches in diameter, whose centre is im- 
mediately opposite to the centre of the square hole (N); both 
centres being in the avis of the pile, which is parallel to P Q, 
the central line of the brass plate E.G; to this circular opening 
a brass circle is attached (moveable round its centre and) having 
four screws (as in figure 2.) by means of which any substance 
intended to be used asa screen may be firmly fixed in the cir- 
cle. Brass plates are made which fit tightly into the circle, 
having rectangular pieces (of different sizes) cut out of their 
centres. : 
c 
rt eetho totson Sel Bey 
> OE Ti Or CSRS 
Having selected one of these plates (in which the opening 
is somewhat smaller than the crystal, or other substance in- 
tended to be used asa screen) it is fixed into the circle be- 
hind the screws (as in figure 3.) and the crystal is then fixed 
in front of it so as to completely cover the opening; the bot- 
tom of the canister (for containing hot water, &c.) is a right~ 
