Standard Resistances
   The certificate accompanying the Standard Ohm at the right reads:

                                              Cavendish Laboratory
                                                    Cambridge 
                                                           August 1884

   This is to certify that the Resistance coil Elliott No. 92 & No. 59 has been compared with the B. A. Units and that its value at a temperature of 18.1°C is 1.00087 BA Units. The B.A. Unit is .9889 Legal Ohms.

                         R. T. Glazebrook
                           Secretary Electrical Standards 
                              Committee of the B. A.

   The instrument is in the Kenyon College Collection. It was sold by Queen of Philadelphia in 1888 for $28.00.

   At the left is a 1000 Ohm standard resistor made by Keiser and Schmidt of Berlin. The coil is wound of manganin, an alloy with a low temperature of resistance, which allowed considerable current to pass through the coil without measurable change of its resistance.

   The resistor was bought by Denison University in 1895 for $10.00.

   During the last decade of the 19th century, physics students at Denison University build apparatus as part of their laboratory curriculum. The students gained valuable experience, and the physics department was able to expand its holdings. 

   The German Silver Ohm at the right was built by Wayland C. Marlowe in 1899. German silver is an alloy of copper and nickel, and has a low temperature coefficient of resistance. 

   Another piece Denison apparatus built by a student is the Arc Lamp Controller, made by E. A. Deeds in 1897.


 

  This tertiary standard ten ohm resistance was bought by the Kenyon College physics department in 1926 to outfit the physics program in a new building, Samuel Mather Science Hall. It was part of a large purchase of apparatus from Leeds & Northrup of Philadelphia, and cost $7.00.

   From the 1927 Leeds & Northrup catalogue" "For measurements requiring individual resistance coils of comparatively high accuracy, but not the extreme accuracy of the [Bureau of Standards Sealed Resistance] standards, ..., we supply individual coils wound on B metal or non-metallic spools, substantially mounted and protected and equipped with bind posts and strap connectors." The strap connections fit neatly into gaps in the L&N student Wheatstone bridges.

   The resistances were good to 1/10 %.

   The apparatus is shown almost life-size.
Return to Electrical Measurements Home Page | Return to Home Page