So 



SCIENTIFIC RECREATIONS. 



TABLE i. 



1 Fahr. = 0-55 Cent, or 0*44 Reamur. 

 i Cent. = -80 Reamur, or r8o Fahr. 

 1 Reamur = 1*25 Cent, or 2*25 Fahr. 



TABLE n. 



Alcohol is used in thermometers in very cold districts, as it does not 

 freeze even at a temperature of 132 Fahr. 



We have now explained the way in which we can measure heat by the 

 expansion of mercury in a tube. We can also find out that solids and 

 gases expand also. Engineers always make allowances for the effects of 

 winter and summer weather when building bridges ; in summer the bridge 

 gets longer, and unless due provision were made it would become strained 

 and weakened. So there are compensating girders, and the structure 

 remains safe. 



The effects of expansion by heat are very great and very destructive 

 at times. Instances of boilers bursting will occur to every reader. It is 

 very important to be able to ascertain the extent to which solid bodies will 

 expand. Such calculations have been made, and are in daily use. 



We can crack a tumbler by pouring hot water into it, or by placing it 

 on the "hob." A few minutes' consideration will assure us that the lower 

 particles of the glass expanded before the rest, and cracked our tumbler. A 

 gradual heating, particularly if the glass be thin, will ensure safety. Thick 

 glass will crack sooner than thin. 



Again, many people at railway stations have asked us, "Why don't they 

 join the rails together on this line ? " We reply that if every length of rail 

 were tightly fixed against its neighbour, the whole railway would be displaced, i 

 The iron expands and joins up close in hot weather. In wet weather, also, 

 the wooden pegs and the sleepers swell with moisture, and get tightened up. 

 Everyone knows how much more smoothly a train travels in warm, wet 

 weather. This is due to the expansion of the iron and the swelling of the 

 sleepers and pegs in the "chairs." A railway 400 miles long expands 338 



