Fire-places and Kitchen Utensils. 485 



with a flat circular plate of sheet copper, like the head 

 of a drum, be interposed between their joinings. These 

 two circular sheets of copper, which form two ends of 

 this very short cylinder, must be perforated in their 

 centres with holes 8 inches in diameter, to give a pas- 

 sage to the steam ; and the ends of the tubes must be 

 firmly fastened to them by means of flanges and rivets. 

 The following figure, which represents an outline of 

 a portion of a steam-tube constructed in this manner, 

 will give a clear idea of this contrivance : 



Fig. 94. 



a, b, are portions of two of the tubes which are united 

 together by means of the short flat cylinder c. 



Now if we suppose one of these tubes (10 feet long) 

 to be immovably fixed in the middle of its length to 

 a beam of wood or to a solid wall, the increase or dimi- 

 nution of the length of each half of it arising from its 

 being occasionally heated to the temperature of boiling 

 water by steam, or cooled to the mean temperature of 

 the air of the atmosphere, being free will cause its two 

 ends to push inwards or to draw outwards the two flat 

 ends of the two neighbouring short cylinders to which 

 they are attached ; and, as these short cylinders are 

 24 inches in diameter, while the tube is only 8 inches 

 in diameter, the -elasticity of the large circular thin 



