148 THE REV. J. G. WOOD. 



therefore, a second frame was constructed of a far 

 stouter character, and this, after a few alterations 

 and improvements had been made, proved perfectly 

 satisfactory, and afforded a clear surface of eleven feet 

 by five feet six inches ; so that a drawing made there- 

 upon was clearly visible in every part of the largest 

 hall: 



Few of those who have seen this great black 

 screen erected upon a lecture platform would be likely 

 to form any idea of the intricacy of the mechanism ; 

 and so perhaps a short description of the apparatus 

 may not be out of place. 



In the first place, each of the two upright posts to 

 which the oblong frame actually bearing the canvas 

 was affixed was composed of two pieces, jointing in 

 with one another, and firmly fastened together by long 

 hand-screws. The oblong frame itself consisted of six 

 parts, two uprights being fastened by screws to the 

 outer poles, and four cross-pieces, capable of being 

 firmly braced together so as to form but two, running 

 from corner to corner of these so as to form the oblong. 

 A stout iron brace in the centre of this completed the 

 actual framework, which was supported by four long 

 guy-ropes running from pegs at the top of the outside 

 poles. 



The canvas was quite a work of art in itself. In 

 the first place, it had to be of a special quality, finely 

 and yet very strongly woven, and, of course, without 

 seam. Then the edges had to be strengthened with 

 broad bands of the very strongest webbing, sewn on 



