and the Existence of active Molecules in Minerals, 7 



properly, the microscope should be placed on a support not 

 liable to be affected by vibrations of any kind, and I therefore 

 placed the instrument on a support made for a telescope 

 stand, so constructed as to prevent vibration w^hen examining 

 the more delicate double stars. I found that even the puls- 

 ation of my body occasioned an oscillatory motion of the par- 

 ticles, when the microscope vs^as placed upon a table. After 

 repeated trials, I became satisfied that whatever motions may 

 appear to take place among the particles, for some time after 

 the drop of water is first placed under the microscope, they 

 will soon subside, if not kept up by agitation from external 

 causes. In London, as an excellent practical philosopher, 

 the late William Nicholson, justly observed, it is scarcely pos- 

 sible to avoid the effects of vibration ; this may be seen by the 

 continual tremours visible on the surface of mercury placed in 

 a basin. Now, if the particles of dust that fall on the surface 

 of the mercury could be brought under a powerful microscope, 

 they would appear in constant motion. Let us suppose the 

 mercury to be changed for water, a similar effect will take 

 place, and the particles that may sink under the surface will 

 represent the particles of dust in a single drop ; and Mr. Brown 

 informs us that the whole of the London dust is composed of 

 active molecules. I am fully conviilced, however, that their 

 activity in a drop of water, as well as when dancing in the 

 sunbeam, is derived from external agitation. The very force 

 of gravity constantly drawing the particles downwards must 

 not be overlooked, for it is not contended that the vitality of 

 inorganic particles is sufficient to keep them permanently sus- 

 pended in water. The observer's breath, and the constant 

 evaporation of the drop, have also a tendency to produce 

 counter-currents. A drop of water placed under the micro- 

 scope, may be regarded as equal, in apparent magnitude, to a 

 quart of the same fluid in a water-glass, and will be subject to 

 the various currents that may be produced by agitation in the 

 larger quantity ; but the slightest movement which occasions 

 a displacement of the particles, even the one-thousandth part 

 of an inch will, under a high magnifying power, make them 

 appear to perform a long voyage. Some of the animalcules 

 discovered by Loewenhoeck, the motions of which excited so 

 much surprise, he informs us, never travelled farther than a 

 hair's breadth.* 



It is highly improbable that we shall ever be able to reduce 

 mineral substances to their ultimate molecules by pulverisation. 



* Hicce progressus non majus habebat spatium quam quod capilli Miame- 

 trum aequaret. 



B 4 



