Arc Light
   The ultimate arc lamp is lightning, and so Benjamin Franklin's 1752 experiment of drawing electricity from the clouds and jumping a spark is perhaps the first arc lamp. In 1801 Humphry Davy observed the brilliant spark obtained when the connection between two carbon rods, attached to the poles of a battery, was broken. Some years later, in a demonstration lecture at the Royal Institution, he produced an arc nearly three inches in length. He used a voltaic battery with 2000 sets of plates, each four inches square. Commercial arc lighting had to wait for the development of dynamos such as the Gramme Machine in the early 1870s. 

   The arc lamp shown in the left and middle photographs below was designed in 1857 by Jules Duboscq and Leon Foucault, and manufactured and sold by Duboscq. The price was 450 francs in the 1885 Duboscq catalogue, and $115 in the 1881 Queen catalogue. The carbons can be seen clearly in the complete instrument at the left. The middle instrument has had its upper carbon holder removed and the coils of the regulating mechanism can be seen. 

   At the right is a diagram of the mechanism. The arc lamp at the right below was made by J.. B. Colt & Co. of New York, and bears a patent date of December 22, 1896.

Washington and Lee University                      Denison University                                         Denison University
   The arc lamps above have automatic controls to keep the spacing between the carbons constant built as part of the mechanism. The separate control was made by physics student E.A. Deeds of the Denison University class of 1897. Deeds later became a trustee of Denison and the president of the National Cash Register Company of Dayton, Ohio. 
   At the left is an arc light on display at the Garland Collection of Classical Physics Apparatus at Vanderbilt University. It has an overall height of 58 cm, and was made by Duboscq of Paris.

   The binding posts on the base and at the top of the upper carbon are the connections for the battery. Instead of (+) and (-), as we would use today, they are labeled "Pôle zinc" and "Pôle charbon".

   The arc lamp at the left is from Kenyon College and uses iron electrodes. The spectrum of iron has thousands of lines, and was sometimes used as a reference. This may have been used by Prof. Elbe H. Johnson, who taught physics at Kenyon from 1914 to 1955 for his doctoral research in optics 
ca. 1925. It is unmarked, but strongly resembles arc lamps made by Gaertner of Chicago. When fitted with carbon electrodes, this lamp was used as a light source for projectors.
   These arcs must have been used for demonstrations, as the spacing between the electrodes would have had to have been adjusted continuously as the electrode material vaporized with use. 

   The carbon arc on the left is at Middlebury College in Vermont. On the right-hand side is an iron arc from the University of Vermont. This is marked with the name of Max Kohl of Chemnitz, but I have been unable to find it in my 1900 Kohl catalogue. 


   The arc lamp at the right in in the Millington/Barnard Collection in the University Museum at the University of Mississippi in Oxford. 

   It is unmarked, but may be some of the apparatus purchased by Frederick A.P. Barnard in the second half of the 1850s. Barnard ordered a good deal of apparatus in this era from French instrument manufacturers, and, in particular, Lerebours et Secretan of Paris. It is not, however, in the 1853 L&S catalogue.

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