Auckland Institute. 517 



illustration of these two forms of energy, I will take the case of lifting a 

 weight, say, one pound one foot high. In lifting this weight 'kinetic 

 muscular energy' has to be exercised in overcoming the force of gravitation of 

 the earth. The pound weight, when supported at the higher level to which it 

 had been raised, represents potential energy to the amount of one unit or 

 foot-pound. The potential energy may be utilized in imparting motion to 

 mechanism during its descent, whereby a unit amount of 'work' is accomplished. 

 A pound of carbon, then, when raised through the space of one foot from the 

 earth represents, mechanically speaking, a unit quantity of energy j but the 

 same pound of carbon being separated or lifted away from oxygen, to which it 

 has a very powerful attraction, is capable of developing no less than 11,000,000 

 foot-pounds or unit quantities of energy whenever the bar to their combination, 

 namely, excessive depression of temperature, is removed — in other words, the 

 mechanical energy set free in the combustion of one pound of pure carbon 

 is the same as would be required to raise 11,000,000 pounds weight one 

 foot high, or as would sustain the work we call a horse-power during five 

 hours thirty -three minutes," a proportion of power, I may observe, enor- 

 mously greater than that which it has yet been found possible to obtain in 

 practice. 



Again, only a very few yeais ago the teaching of chemistry all leant on the 

 statical theory ] that is to say, it was taken for granted that when a particle, 

 of an acid for instance, had combined with an equivalent of base to form a 

 neutral salt, that the energies of the constituents were exhausted, or at all 

 events dormant, until again called forth by a stronger elective affinity. In 

 words which I quote from the address of Professor Williamson, "these 

 chemists only took cognizance of those changes of place amongst the atoms of 

 the re-agents they dealt with, which resulted in the disappearance of the 

 molecules employed and the appearance of new molecules formed by their 

 reaction on one another ; thus, when a solution of common salt (chloride of 

 sodium) is mixed with a solution of nitrate of silver, it is well known that the 

 metallic atoms in these respective compounds change places with one another, 

 forming nitrate of soda and chloride of silver ; for the silver salt soon settles 

 to the bottom of the solution in the form of an insoluble powder, while the 

 other product remains dissolved in the liquid. But as long as the solution of 

 the salt remained undecomposed, each little molecule of it was supposed to be 

 chemically at rest." But the author of the paper from which I am quoting — 

 Professor Williamson — pointed out, many years ago, that molecules which 

 appeared to be chemically at rest are reacting on one another when in suitable 

 conditions, in the same kind of way as those which are manifestly in a state of 

 chemical change j that is, that the forces are not dead or exhausted by the act 

 of the entering of the molecules into a stable combination, but that they 



