SCIENCE OF COMMON THINGS. 187 



Why clocks go faster in summer than in winter. 



Because the metal of the stove contracts, by reason 

 of a reduction of temperature, when the fire is extin- 

 guished. 



1336 Why are the nails in almost all old houses loose and easily 

 drawn out ? 



Because the iron expands in the summer, and con- 

 tracts in the winter, more than the stone or wood, and 

 thus the opening is gradually enlarged after a lapse of 

 time. 



133*7 Why does a piano give a higher tone in a cold than in a warm 

 room f 



Because in a cold room the strings are contracted 

 and tighter. 



1333 Why do clocks go slower in summer and faster in winter? 



Because the pendulums elongate in summer through 

 the effects of heat, and consequently vibrate slower ; 

 while in winter they contract, become shorter, and 

 vibrate more rapidly. 



1339 Hoiu is this inequality in the rate of motion in timepieces obviated f 



By what is called a compensating pendulum / that 

 is, one constructed of two metals, possessing different 

 expansive powers, in such a manner that the greater 

 expansion of one bar in one direction equals the less 

 expansion of other bars in a different direction, and 

 thus maintain an invariable length of the pendulum. 



1340 Does wood expand under the influence of heat differently from 

 metal ? 



Yes ; an iron bar expands and contracts equally in 

 all directions, but wood expands and contracts more in 

 breadth than in length. 



134:1 Why will a person, buying oil, molasses, spirits, etc., by the mea- 

 sure, get a greater weight of the same material in the same measure in the 

 winter tiian in the summer ? 



Because these liquids contract and occupy less space 

 in the winter than in summer ; consequently it requires 

 more of the same kind to fill the same space in winter 

 than in summer. 



1343 How can heat be measured f 



Only by its effects : since the magnitude of any body 



