Brunonian or Particle Movements. 177 



their rotations and gyrations till the weeks pass into months, can 

 accept the observation that the movements last but a brief time. 

 The lives of low organisms last often but a few hours, but these 

 Brunonian movements go on from month to month. And what 

 is the cause of it all? It is to be found in the action and 

 reaction of the surface film of the particles and the opposing 

 film of the liquid medium in Avhich the particle rests or floats. 

 One may gather so much by watching closely the nature of the 

 movements, which are readily seen to be oscillatory and not 

 transitional. The particles undergoing Brunonian movements 

 only rarely travel any distance ; they confine their activity to a 

 very limited area. When they collide they are seen to possess 

 but small momentum. And when the smaller particles do move 

 any appreciable distance it may be considered due to the convec- 

 tion current in the water set up by the motion of some larger 

 particle. 



These Brunonian movements are being constantly met with 

 by those who work with a fairly high power of the microscope. 

 They are not easily seen by a lower power than a combination 

 amplifying 200 diameters. By a power of 500 or 600 diameters 

 they are excellently well seen. And when one gets accustomed 

 to watching them the eye readily distinguishes between them and 

 the somewhat similar movements of bacteria like the vibriones. 

 We are continually finding reference to them in the scientific 

 journals. Let us take up a volume at random. Here is the 

 Journal of the Royal Microscopical Society for 1881. At page 

 877 we find an extract from Les comptes Rendus (of the French 

 Academy):— "M. Girod, investigating the ink-bag of the Sepia 

 officinalis (that is, the cuttle fish), writes that under the micro- 

 scope the ink is seen to contain a number of minute corpuscles 

 floating in transparent serum and manifesting Brownian move- 

 ments when placed in fresh water." 



Pass over thirty years or so and we find in the volume of 

 "Nature " for 1908, in a letter on the subject of mercury forming 

 bubbles with water and with air, an observation on the formation 

 of a scum of oxide of mercury, which on microscopic examination 

 shows what are called pedetic movements. These are the 

 Brunonian movements; and mercury and its combinations are 



