GO Royal Institution : — 



chemical affinity. A collodion balloon filled with a mixture of 

 chlorine and hydrogen was hung in the focus of a parabolic mirror, 

 and in the focus of a second mirror 20 feet distant a strong electric 

 light was suddenly generated ; the instant the light fell upon the 

 balloon, the atoms within it fell together with explosion, and hydro- 

 chloric acid was the result. The burning of charcoal in oxygen was 

 an old experiment, but it had now a significance beyond what it used 

 to have ; we now regard the act of combination on the part of the 

 atoms of oxygen and coal exactly as we regard the clashing of a 

 falling weight against the earth. And the heat produced in both 

 cases is referable to a common cause. This glowing diamond, w r hich 

 burns in oxygen as a star of white light, glows and burns in con- 

 sequence of the falling of the atoms of oxygen against it. And 

 could we measure the velocity of the atoms when they clash, and 

 could we find their number and weight, multiplying the mass of 

 each atom by the square of its velocity, and adding all together, we 

 should get a number representing the exact amount of heat de- 

 veloped by the union of the oxygen and carbon. 



Thus far we have regarded the heat developed by the clashing of 

 sensible masses and of atoms. Work is expended in giving motion 

 to these atoms or masses, and heat is developed. But we reverse 

 this process daily, and by the expenditure of heat execute work. 

 We can raise a weight by heat ; and in this agent we possess an 

 enormous store of mechanical power. This pound of coal, which 

 I hold in my hand, produces by its combination with oxygen an 

 amount of heat which, if mechanically applied, would suffice to raise 

 a weight of 100 lbs. to a height of 20 miles above the earth's sur- 

 face. Conversely, 100 lbs. falling from a height of 20 miles, and 

 striking against the earth, would generate an amount of heat equal 

 to that developed by the combustion of a pound of coal. Wherever 

 work is done by heat, heat disappears. A gun which fires a ball 

 is less heated than one which fires blank cartridge. The quantity 

 of heat communicated to the boiler of a working steam-engine is 

 greater than that which could be obtained from the recondensation 

 of the steam after it had done its work ; and the amount of work 

 performed is the exact equivalent of the amount of heat lost. Mr. 

 Smyth informed us in his interesting discourse, that we dig annually 

 84 millions of tons of coal from our pits. The amount of mechani- 

 cal force represented by this quantity of coal seems perfectly fabulous. 

 The combustion of a single pound of coal, supposing it to take 

 place in a minute, would be equivalent to the work of 300 horses ; 

 and if we suppose 108 millions of horses working day and night 

 with unimpaired strength, for a year, their united energies would 

 enable them to perform an amount of work just equivalent to that 

 which the annual produce of our coal-fields would be able to ac- 

 complish. 



Comparing with ordinary gravity the energy of the force with 

 which oxygen and carbon unite together, the chemical affinity seems 

 almost infinite. But let us give gravity fair play ; let us permit it 

 to act throughout its entire range. Place a body at such a distance 



