The Propagation of Heat 



189 



the particles of which are not free to move over and 

 around one another, as is the case with liquids. Gases 

 resemble liquids in this respect, the motion of their 

 particles being even less restricted than that of liquid 

 particles. The setting up of convection currents in 

 a gas by the application of heat is described in the 

 next experiment. 



It 



M 



'J 



Fig. 59. 



EXPERIMENT 70. The necessary apparatus consists 

 of a flat cardboard or wooden box a large cigar-box 

 answers admirably with all apertures such as the 

 cracks around the edges of the lid carefully sealed by 

 pasting paper over them. Two holes are made in the 

 lid of sufficient size to admit the ends of wide glass 

 tubes, such as Argand lamp chimneys, and the latter 

 are kept in position as shown in Fig. 59 by bands 

 of wide rubber tubing or by a plaster of Paris seal. 



