106 
ELEMENTARY CHEMICAL MICROSCOPY 
particles enters the microscope and eventually the eye of the 
observer, and that therefore he never sees the particles them¬ 
selves, but merely a diffraction disk of light. We know of the 
existence of these particles through the same manifestation of 
more or less scintillating points of light that we see in the fixed 
stars on a moonless night. As hereinbefore stated the image 
of a point of light is a diffraction disk surrounded by alternate 
dark and bright rings. These diffraction disks appear to be 
in rapid motion. They appear to spin, to expand or contract 
and are endowed with a constant vibratory movement. This 
is due to the fact that exceedingly minute particles suspended 
in a liquid exhibit a constant vibratory and rotatory motion, 
long called the Brownian movement and now known to be associ¬ 
ated with and a manifestation of what we commonly term molec¬ 
ular vibration or bombardment. The presence of disintegrating 
or so-called peptizing ” colloids increases the Brownian 
motion, while electrolytes by reason of their causing agglutina¬ 
tion tend to decrease the amplitude of the paths of vibration. 
In the few years that ultramicroscopic research has become 
possible a large number of investigations have been made upon 
the amplitude of the paths of vibration of the finest of these 
infinitely small suspended particles, with the result that the 
measurements made agree very closely with the theoretical 
values computed for the amplitudes of vibration of the molecules. 
Agencies which increase molecular vibration, such as heat, 
dilution and consequent reduction of viscosity, increase the 
Brownian movement. Hence, we find under the ultramicroscope 
the suspended particles in a gas (as, for example, in smoke) 
in much more rapid motion than in a liquid, while in a solid the 
Brownian movement is visible only with the greatest difficulty. 
Since the tiny particles in suspension are being bombarded 
on all sides, the motion imparted to them must be the resultant 
of the forces acting; we therefore find them spinning rapidly as 
well as moving to and fro. Some authors have even suggested 
that the term kryptokinetic motion be assigned to the rotatory 
movement to distinguish it from the oscillating Brownian vi¬ 
bration. 
