George B. Manhart's 1962 history of DePauw University (Greencastle, Indiana), DePauw Through the Years, has only two sentences about Prof. Joseph P. Naylor of Physics: "Prof. Naylor had come... in 1891, and continued through 1925, when he became professor emeritus. His skill in constructing laboratory equipment was especially helpful in view of the small appropriations available." This page is about Naylor's apparatus.

   Naylor did undergraduate work at Adrian College in Michigan, and was a draftsman and a high school physics teacher before becoming one of the first students to receive an M.S. in physics from Indiana University in 1885. Indiana immediately hired him as a professor of physics, and four years later he he resigned as head of the Indiana physics department and came to DePauw.

   In March 1985 I visited DePauw, and discovered that at least fifteen pieces of apparatus made by Naylor were still in existence. The majority of them are for electrical measurements: six galvanometers, a quadrant electrometer, a telescope and scale holder, and a Kelvin bridge. In addition, there is an optical bench, a sonometer and a  heliostat, along with two standard  electroscopes and one Zeleny electroscope. Naylor used hardwood in the same way that most of us use metal: he machined it. The edges of the pieces are sharp and square, and the scribed center lines are often visible. The coils are wound with care, with every turn in place.

A. Galvanometers

In the view at the right of one of Naylor's D'Arsonval galvanometers, the back, which protects the suspension from damage, has been removed. The permanent magnets, with curved pole faces and a cylinder of soft iron to shape the magnetic field, can be seen clearly.     This galvanometer, like the one below, has an unusually long torsion fiber.     The porthole in the front allows the mirror attached to the coil to be seen.

Another design of a D'Arsonval galvanometer by Naylor. In this case, two bar magnets appear to have been combined with a yoke and pole faces to form a U-magnet.    This galvanometer has suffered some damage. The glass over the porthole to the mirror is not in place, and the protective back panel is missing.

One of the coils has been taken off this differential galvanometer built by Naylor, showing the rotating mirror attached above the magnetic needles. The coils are carefully wound and have square edges.

This example of an astatic, Kelvin-type differential galvanometer made by Naylor has a pivot on which the entire apparatus may revolve on its base.

This Wiedemann galvanometer is the most ambitious piece of surviving Naylor apparatus. The magnetic vanes are contained in a copper container (in the center of the apparatus between the two coils) for damping purposes. A compensator for the earth's magnetic field is attached to the tube supporting the top of the suspension.

My notes from 1985 say that an air-damping vane was attached below the suspended coil in this unusual form of galvanometer. The presence of Helmholtz coils suggest that this is a tangent galvanometer.

B. Other Electrical Measurements Apparatus

Naylor's quadrant electrometer has suffered over the years. The four quarter-circles of brass are all that remain of the quadrants used to attracted the suspended aluminum vane which can just be seen in front of the base. A sliding metal side was removed when the picture was taken.

The motions of the magnetic needles or vanes of all of these instruments are hard to observe. To make the degree of rotation visible, tiny, light mirrors are attached to the lower portion of the suspension fiber, a design dating back to 1853.    Naylor built his own version of a commercial scale and telescope holder to make quantitative measurements of galvanometer deflections. The scale is attached to the flat, vertical board in the middle, and the telescope is held perpendicular to it by the U-clamp. The telescope is pointed toward the mirror, and, after suitable tweaking of the adjustment screws, the reflection of the scale can be seen. The readings are not linear unless a curved scale is used.

I think that this is a Kelvin bridge, which is a form of  Carey Foster bridge.