17 



third plays between the second and fourth (.or bottom board). Between 

 the boards are frames of wood to support the leather. Three of the boards 

 are so furnished with valves and other apparatus that the machine, when 

 covered with leather and fitted up, works like a double actino- steam 

 cylinder, the space between the two upper boards forming the common 

 chamber, whence the air is conveyed through the pipe to the fire. 

 Upon the third board going down the air will rush in and fill the space 

 between the second and third boards ; upon the same board ^ -» up 

 the air will rush in and .fill the space between the third and*^' fourth 

 boards ; when the rack staflT is pulled down the air is forced from be- 

 tween the second and third boards into the chamber between the first 

 and second boards ; when the staff returns the air is driven from be- 

 tween the third and fourth boards into the same chamber ; thus, when 

 the staff rises or falls the air is forced into the common chamber, by 

 which means a middle pipe is supported, and a constant and steady, as 

 well as powerful blast is obtained, capable of fusing a bar of iron when 

 one end of it is made red hot. 



55. An Odontograph. — By Professor Willis, of Cambridge. 

 This instrument is intended for setting out the forms of teeth, 

 so that any two wheels of a set may work truly together. — Vide 

 Trans, of Civil Engineers, Vol. II. p. 2. 



56. Specimens of Scales of equal parts. — By Charles H. 

 HoIzapfFel. — These scales are applicable to various purposes of 

 engineering, architecture, and general science. 



57. Bate''s Anaglyptograph for representing relieved sur- 

 faces. — By the use of this machine lights and shadows are truly 

 represented. 



58. Model of a Life Preserver.— By J. Clark, of York.— 

 To be put on as a short jacket, buttoned and buckled in front ; 

 made of jean prepared with caoutchouc and perfectly air tight; 

 on this is another covering of jean, and the whole is inclosed in 

 caoutchouc. 



