VAPOUR. 155 



open sea. They run on the top of the sea, and are called 

 Petrels, or rather Peter-els, from " St. Peter," in allusion to 

 his walking on the sea, to go to Jesus.) 



Q. Why do CANDLES and LAMPS SPIRT 

 when RAIN is at hand? 



A. Because the air is filed with 

 vapour, and the humidity penetrates the 

 wick ; where (being formed into steam} 

 it expands suddenly, and produces a 

 little explosion. 



Q. Why does a DROP of WATER sometimes 

 ROLL along a piece of hot iron without leaving the 

 least trace ? 



A. If the iron be very hot indeed, 

 the bottom of the drop is turned into 

 vapour, before the drop can evaporate; 

 and the vapour thus formed buoys the 

 drop up, without allowing it to touch the 

 iron at all. 



Q. Why does it ROLL ? 



A. The current of air (which is 

 always passing over the heated surface) 

 drives it along. 



Q. Why does a LAUNDRESS put a little 

 SALIVA on an IRONING-BOX to know if it be hot 

 enough ? 



A. Ff the saliva sticks to the box and 



