Energy and Heat 125 



and then, by carefully fanning the glowing portion, 

 flame is at length obtained. 



81. It has been indicated in the preceding para- 

 graphs that heat is a form of energy, or, in other words, 

 that a hot body is capable of doing work, on account 

 of its hotness. After the description and consideration 

 of some simple experiments dealing with hot bodies, 

 the nature of heat will receive further explanation. 



EXPERIMENT 39. Arrange a poker, or other long 

 bar of metal, upon sets of wooden blocks as shewn 

 in Fig. 34. One end is kept in a fixed position by 

 means of a 14 Ib. weight, while the other rests upon 

 a knitting-needle, which is lying on the surface of a 

 sheet of glass placed on top of one of the wooden blocks. 

 One end of the needle is thrust through the middle 

 of a long straw so that the straw is at right angles to 

 the needle. The hole in the straw must not be large 

 enough to allow it to slip around the needle. Arrange 

 the needle and straw in such a way that the straw 

 is in a vertical position at the beginning of the 

 experiment. Heat the middle portion of the poker 

 by means of two or three good Bunsen burners. (If 

 obtainable, a specially constructed burner, known as a 

 Ramsay burner, which gives a Bunsen flame of a long 

 flat shape, may be substituted for the ordinary Bunsen 

 burners, as shown in the figure.) Soon after the 

 heating has started, the straw will be seen to travel 

 round in such a fashion that its top end moves forward 

 in the direction of the end of the poker which rests on 

 the needle. This movement of the .straw will continue 

 for some time, but at length it will reach a position 

 in which it will remain practically steady as long as 

 the heating with the original burners is maintained. 

 Remove the burners and allow the poker to cool down. 



