188 Things not generally Known. 



HEAT AND EVAPOKATION. 



In a communication made to the French Academy, M. 

 Daubree calculates that the Evaporation of the Water on the 

 surface of the globe employs a quantity of heat about equal to 

 one-third of what is received from the sun ; or, in other words, 

 equal to the melting of a bed of ice nearly thirty-five feet in 

 thickness if spread over the globe. 



HEAT AND MECHANICAL POWEK. 



It has been found that Heat and Mechanical Power are 

 mutually convertible ; and that the relation between them is 

 definite, 772 foot-pounds of motive power being equivalent to 

 a unit of heat, that is, to the amount of heat requisite to raise a 

 pound of water through one degree of Fahrenheit. 



HEAT OF MINES. 



One cause of the great Heat of many of our deep Mines, 

 which appears to have been entirely lost sight of, is the chemi- 

 cal action going on upon large masses of pyritic matter in their 

 vicinity. The heat, which is so oppressive in the United Mines 

 in Cornwall that the miners work nearly naked, and bathe in 

 water at 80 to cool themselves, is without doubt due to the 

 decomposition of immense quantities of the sulphurets of iron 

 and copper known to be in this condition at a short distance 

 from these mineral works. R. Hunt, F.R.S. 



VIBRATION OF HEATED METALS. 



Mr. Arthur Trevelyan discovered accidentally that a bar of 

 iron, when heated and placed with one end on a solid block 

 of lead, in cooling vibrates considerably, and produces sounds 

 similar to those of an ^Eolian harp. The same effect is pro- 

 duced by bars of copper, zinc, brass, and bell-metal, when 

 heated and placed on blocks of lead, tin, or pewter. The bars 

 were four inches long, one inch and a half wide, and three- 

 eighths of an inch thick. 



The conditions essential to these experiments are, That two 

 different metals must be employed the one soft and possessed 

 of moderate conducting powers, viz. lead or tin, the other hard ; 

 and it matters not whether soft metal be employed for the bar 

 or block, provided the soft metal be cold and the hard metal 

 heated. 



That the surface of the block shall be uneven, for when ren- 

 dered quite smooth the vibration does not take place ; but the 

 bar cannot be too smooth. 



That no matter be interposed, else it will prevent vibration, 



