Ultramicroscope
Encyclopedia
An ultramicroscope is a system of illumination for viewing tiny particles. When the diameter of a particle is below or near the wavelength of light (around 500 nanometers), the particle cannot be seen in a light microscope with the usual method of illumination. The ultramicroscope system is based on light scattering
Light scattering
Light scattering is a form of scattering in which light is the form of propagating energy which is scattered. Light scattering can be thought of as the deflection of a ray from a straight path, for example by irregularities in the propagation medium, particles, or in the interface between two media...

, not light reflection
Reflection (physics)
Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...

. In the system, the particles to be observed are dispersed in a liquid or gas colloid
Colloid
A colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...

 (or less often in a coarser suspension
Suspension (chemistry)
In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase is dispersed throughout the external phase through mechanical agitation, with the use of certain...

). The colloid is placed in a light-absorbing, dark enclosure, and illuminated with a convergent beam of intense light entering from one side. Light hitting the colloid particles will get scattered. In discussions about light scattering, the converging beam is called a "Tyndall cone". The scene is viewed through an ordinary microscope placed at right angles to the direction of the lightbeam. Under the microscope, the individual particles will appear as small fuzzy spots of light moving irregularly. The spots are inherently fuzzy because light scattering produces fuzzier images than light reflection. The particles are in Brownian motion
Brownian motion
Brownian motion or pedesis is the presumably random drifting of particles suspended in a fluid or the mathematical model used to describe such random movements, which is often called a particle theory.The mathematical model of Brownian motion has several real-world applications...

 in most kinds of liquid and gas colloids, which causes the movement of the spots. The ultramicroscope system can also be used to observe tiny nontransparent particles dispersed in a transparent solid or gel.

Ultramicroscopes have been used for general observation of aerosols and colloids, and in the study of Brownian motion
Brownian motion
Brownian motion or pedesis is the presumably random drifting of particles suspended in a fluid or the mathematical model used to describe such random movements, which is often called a particle theory.The mathematical model of Brownian motion has several real-world applications...

, and in observing ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

ization tracks in cloud chamber
Cloud chamber
The cloud chamber, also known as the Wilson chamber, is a particle detector used for detecting ionizing radiation. In its most basic form, a cloud chamber is a sealed environment containing a supersaturated vapor of water or alcohol. When a charged particle interacts with the mixture, it ionizes it...

s.

The ultramicroscope was developed by Richard Adolf Zsigmondy
Richard Adolf Zsigmondy
Richard Adolf Zsigmondy was an Austrian-Hungarian chemist and Nobel laureate for chemistry known for his research in colloids. The crater Zsigmondy on the Moon is named in his honour....

 (1865 - 1929), who was awarded a Nobel Prize in 1925 for his research on colloids and the ultramicroscope. The ultra in ultramicroscope refers to the ability to see objects whose size is shorter than the wavelength of visible light, on the model of the ultra in 'ultraviolet'.

For a different type of microscopy that also leverages light scattering against a dark background see dark field microscopy
Dark field microscopy
Dark field microscopy describes microscopy methods, in both light and electron microscopy, which exclude the unscattered beam from the image. As a result, the field around the specimen Dark field microscopy (dark ground microscopy) describes microscopy methods, in both light and electron...

.
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