Brunonian or Particle Movements. 179 



water comes to the solid, and then there is another alteration of 

 density and further movement, and so on. 



In order to demonstrate these movements there are a couple 

 of "preparations" under these microscopes, which can be 

 examined after the lecture. 



The microscopes are of comparatively high power, and it is 

 not every one who is accustomed to the use of these powers. But 

 I can make clear to all without the aid of a microscope that these 

 movements take place. I put some grains of camphor on the 

 surface of this water. The alteration of density in the layers near 

 the camphor causes the movement you see. [Experiment.] The 

 pieces of camphor are performing the Brunonian movements on 

 a macro scale. 



A similar explanation holds true in regard to the movements 

 of minute particles of matter not usually regarded as soluble in 

 water, as sand or clay. The particles, it must be remembered, 

 are very minute. Matter in a minute state of division acts differ- 

 ently in the air than when in bulk; molecular matter acts more 

 rapidly than molar. Iron rails and ships and bridges are fairly 

 lasting according to experience. But prepare iron in a minute 

 state of division by heating the oxide in a current of hydrogen 

 and throw it suddenly into the air. It catches fire and burns ! 

 The minute state of division causes the oxidation, slow in the 

 mass, to be rapid, even to burning. Thus the particles of 

 matter regarded as insoluble in bulk are really surrounded by a 

 film of "weathered" or oxidised material which is invisible. 

 The particles themselves are only visible to a high microscopic 

 power; much less visible must be this film; and the Brunonian 

 movements are due to the action of this film. Lord Kelvin in 

 one of his popular lectures refers to this subject in the case of 

 the Brande bars, which are bars of steel showing colours due to 

 a fine film of oxidation, and were bequeathed by Professor Brande 

 to the Royal Institution, where they are kept in the charge of 

 Professor Sir James Dewar (another eminent Englishman hailing 

 from Scotland). And Lord Kelvin shows how these are films of 

 oxidation, which are utterly invisible, yet which can V)e shown to 

 exist by electrical means. Invisibility, of course, is of absolutely 

 no value as a criterion where either matter or force is concerned. 

 The air is round about us, and the chemistrv of it has been 



