Scientific Lectures. 129 



in this course by Prof. G. F. Barker, I will pass from this grand 

 theme to lesser lights and mere mundane sources ot illumination. 



The first of these as regards its extent and importance is combus- 

 tion, a very intense class of chemical combination. 



When two substances enter into this sort of union, we may well 

 conceive of their atoms as rushing violently together like contending 

 armies in the clash of conflict, and then nothing is more natural than 

 to suppose that the impact of the combining atoms should give rise to 

 vibrations, whose intensity and violence should be in proportion to 

 the energy of the actuating attraction. Passing by the ordinary 

 illustrations with which we are every day and night made familiar in 

 the light of fires, lamps, candles and gas flames, I will go at once to 

 one of the most striking instances which is furnished us in the oxy- 

 hydrogen blowpipe. Here we have a nozzle from which hydrogen, 

 one of the most combustible of gases, issues in a large volume, burn- 

 ing, when ignited, with an immense flame. 



Into the center of this is driven a stream of oxygen gas, which is a 

 body with which hydrogen combines with the greatest energy. Its 

 effect, as you see, is to diminish the fize of the flame, but, as I will 

 presently show you, vastly to increase its intensity. 



(The apparatus, consisting of a large copper hydrogen generator, a 

 cylinder of compressed oxygen, and the blowpipe, supported on a 

 light stand, was standing on a platform built upon one of the stage 

 traps and on a level with the floor. At this point the speaker, stand- 

 ing by his apparatus, made a signal, at which the trap was raised, so 

 lifting all to a height of some ten feet above the floor. The height of 

 the jet, being about four feet more, gave a considerable elevation. A 

 bar of steel was first submitted to the action of the jet, and, being 

 continuously fed forward as it was melted and dissipated, produced a 

 cascade of sparks and scintillative globules, which, poured upon the 

 stage, rebounded from metal plates placed to receive them and rolled 

 in a torrent of minute sparks into the sunken footlights. Rods 

 of cast-iron were then burned in like manner, with the production 

 of large flower-like scintillation, but with less brilliant general 

 effect; and, finally, the entire building was illuminated by the com- 

 bustion of a bundle of magnesium wire similarly treated. The trap 

 having been again lowered during this last experiment, the lecturer 

 resumed.) 



Some of you may, no doubt, be inclined to ask, If the source of the 

 light was the vibration due to the combination of the oxygen and 

 hydrogen, why was the brilliant light only seen when the solid metals 

 [Inst.] 9 



