and the Mode of its Communication. 51 



both sides, first with thick cartridge paper, and then 

 with what is called gilt paper; the metallic substance 

 (copper) with which one side of the paper is covered 

 being on the outside. 



o 



To support a movable screen of this kind in a ver- 

 tical position, it must of course be provided with a foot 

 or stand. Those I use are fastened to one side of a 

 pillar of wood by two screws, one of which passes 

 through the centre of the screen where the cross-bars 

 belonging to the frame of the screen meet, and the 

 other through the middle of the piece of wood which 

 forms the bottom of the screen. This pillar of wood, 

 which is turned in a lathe, is I2|- inches high, and 

 is firmly fixed, at its lower end, in a piece of wood 

 8 inches square and i inch thick, which serves as a stand 

 or foot for supporting it. 



As, in making experiments with this thermoscopt, it is 

 frequently necessary to remove the hot bodies that are 

 presented to it farther from it or to bring them nearer 

 to it, in order that this may be done easily and expedi- 

 tiously by one person, and without its being necessary 

 for him to remove his eye from the bubble (which he 

 should constantly have in his view), I make use of a 

 simple machine, which I have found to be very useful. 



It is a long and shallow wooden box, open at both 

 ends. It is 6 feet long, 12 inches wide, and 5 inches 

 deep, measured on the outside ; its vertical sides are 

 made of i|--inch deal; its bottom and top, of inch deal. 

 A part only of the top or cover of this box is fixed 

 down on the sides, and is immovable. The part of 

 the cover which is fixed, and on which the thermoscope 

 is placed, occupies the middle of the box, and is 13 

 inches in length. On the right and left of this fixed 



