ISO 



LECTURES TO SCIENCE TEACHERS. 



ential air-thermometer. There is a bent tube with liquid 

 in the centre of it terminating in two bulbs. If one of 

 those bulbs is heated the air in it expands considerably, 

 and this will be shown by a rising of the liquid in one arm 

 of the tube and a sinking in the other arm, whereas if it 

 were cooled the contrary would take place and the liquid 

 would actually descend in this arm and rise in that arm. 

 This instrument, together with an apparatus called a 

 Leslie's cube, which consists of a cube of metal with sur- 



Fio. 2. 



faces of different natures, some highly polished, others 

 blackened or whitened, and so forth, were the chief things 

 employed by Leslie. He arrives at the result that different 

 surfaces radiate heat to different extents. Thus if he em- 

 ployed a polished surface and heated the cube with boiling 

 water, the thermometer was much less heated by radiation 

 than if he employed either a, black surface or a white sur- 

 face \ in fact, he drew out a table of a large number of 

 different substances, and showed the relative different 



