| Nineteenth century students often used a vertical spectrometer
to study reflection and refraction. At the right is a spectrometer made for
this purpose by Duboscq. At the center of the circle is a glass prism. By
adjusting the position of the prism until the angle of minimum deviation is
obtained, the experimenter can find the index of refraction of the glass.
Other uses of this apparatus are shown in the other instruments on this page.
This apparatus was made by Duboscq of Paris, and is in the collection of Allegheny College in Meadville, Pennsylvania.
In the latter part of the nineteenth century this apparatus was replaced by the optical disk, an instrument that allowed a wider range of optical demonstrations and experiments to be performed.
| At the left is an piece of apparatus in the collection
of National Museum of American History at the Smithsonian Institution in Washington,
It was made by the firm of Lerebours et Secretan of Paris, and is listed at 250 francs ($50) in the 1853 catalogue.
In the picture the apparatus is set up for demonstrations of the law of specular reflection, although the reflecting surface needs to be rotated more toward the vertical. Vernier scales are provided to allow greater precision in measuring the angles of incidence and reflection.
To study Snell's law, the upper arm must be moved from the first to the second quadrant, and the reflecting surface replaced by a semicircular glass disk or a circular glass container half full of water, similar to the glass container in the apparatus below.
In its original form, Snell's law referred not to angles but to the vertical distances between the point of refraction and the horizontal line drawn between the points where the incident and refracted rays pass through a circle drawn around the refracting point, and the normal to the surface. The counterbalanced pivoting arms allow these distances to be measured.
| This device was made by Duboscq of Paris. Americans could
buy it for $65 from James W. Queen of Philadelphia. The 1888 Queen Illustrated
Catalogue of Instruments used in Physical Optics notes that it "represents
a neat and accurate instrument for verifying the laws of refraction and total
reflection. It consists of a vertical divided circle, to which is attached
a circular glass tank, half filled with water or some other transparent liquid.
The surface of the liquid must coincide exactly with the 90° on the scale.
The angles of incidence and refraction can be read off at the verniers, carried
by the two arms, and the sines directly measured by means of the graduated
horizontal sliding scale."
It is in the Garland Collection of Classical Physics Apparatus at Vanderbilt University in Nashville, Tennessee.
|| This is a Duboscq/Pellin version of the apparatus shown
in several place above, and dates from the beginning of the 20th century.
In is in the collection of Franklin and Marshall College in Lancaster, Pennsylvania.
| This reflection and refraction demonstrator is at the University
of Texas in Austin. Since the University was founded in 1890, this apparatus
respresents some of its earliest equipment.
The device is the same as that at the Garland Collection at Vanderbilt with the glass water tank removed. Prisms and reflecting surfaces were attached to the center of the device for other demonstrations.
The arms of the reflection, refraction and polarization apparatus at the right are both pivoted down; in use, one or both would be raised.
The apparatus is by Pixii of Paris, and bears the date of 1849. The reflecting plate can be fixed horizontally at the center. One of the pieces at the bottom is Fresnel's rhomb, but it has lost its glass.
The apparatus is at Hobart and William Smith Colleges in Geneva, New York.