Page:Light waves and their uses.djvu/61

Rh extreme minuteness of light waves their bending around obstacles may be readily observed.

2. The extreme minuteness of light waves renders it possible to utilize the microscope and the telescope as instruments of great precision. These instruments depend on the property of the objective of gathering together waves from a point so that they are concentrated in the diffraction pattern which is called the image.

3. The accuracy of measurement is still further increased by modifying the telescope or microscope so as to utilize only two pencils, thus converting these instruments into interferometers.

4. By the device of separating the two pencils and reuniting them by reflections from plane-parallel surfaces, the fringes may be made as large as we please without diminishing the brightness of the light, and hence the accuracy of measurement may be correspondingly increased.