The hemispherical bell is made to vibrate by stroking it with a violin bow. If the resonating cylinder is turned toward the bell and its length adjusted by the slide until its resonate frequency matches that of the bell, the sound is intensified. The cylinder can be moved away from the bell and tilted up and down. This piece of equipment cost $20 when it was purchased from Queen & Co. of Philadelphia.

This probably is the x-ray tube Professor Almy used to produce his first x-ray photographs in February 1896.

A photographs taken by Professor Almy in February 1896. The colors are the result of fading. Originally all would have been black and white.

A photograph taken by Professor Almy in February 1896. The colors are the result of fading. Originally all would have been black and white.

A photograph taken by Professor Almy in February 1896. The colors are the result of fading. Originally all would have been black and white.

The chronograph was used in conjuction with a transit telescope to make a correction to a clock. The drum was covered with a sheet of paper, and a pen-holding mechanism, now lost, moved along the length of the drum as the drum rotated. The pen made a continuous line on the paper. The pen mechanism was connected to a clock which put out an electrical pulse every second, and those pulses made jogs in the line. An observer at a transit telescope watched for the passage of a star through the meridian, and when the star crossed the cross-hairs of the telescope, the observer closed a switch which produced a different sort of jog in the line. It was then possible to determine within a small fraction of a second what the clock read when the star crossed the meridian. The drum was turned by a spring motor, and the governor to control the speed is in the upper right of the picture. This was part of the equipment in the Grinnell College observatory in the late 1800s.

This chronometer is five inches in diameter. It is mounted in a box with a glass lid (below the wooden lid) and is in gimbals for use on a ship. The lettering on the face reads Ulysse Nardin Locle Suisse A tag with the chronometer says that it was checked by the US Naval Observatory on September 28, 1945.

A solar microscope was placed in a hole in a window shutter with the mirror outside and the barrel extending into a room. Sunlight was reflected by the mirror through condensing lenses, a slide carrying an object to be observed, and projection lenses. The image was projected on a screen in the room. This microscope has no maker's name on it, and its date is unknown. The solar microscope was invented in 1740 and remained popular into the next century. This instrument probably is older than Grinnell College, possibly dating to the late 18th century and certainly no later than the early 19th century.

This "talking machine" is on loan to the museum by the family of Professor Ben Graham. They used it in Massachusetts in the late 1890's. The recording is on a wax cylinder instead of a flat disk. The horn is not original; the original horn was much larger.

This small chronometer, about three inches in diameter, was made by Northwest Instrument Company of Seattle, Washington. The date of manufacture is unknown. It is mounted in gimbals for use on a ship.

This telescope has a mahogany tube and five brass draw sections. It was sold by and probably made by Queen & Co. Date of acquisition is not known

This is a very sensitive galvanometer, patterned after one built by Lord Kelvin. This type galvanometer is capable of detecting a current as small as 10 picoamperes for a deflection of 1 mm at a distance of 1 m. Within each of the two brass cylinders are two facing coils, and in the center of the cylinder, betrween the coils, is a small piece of mica with five short magnetized needles glued to it. On each mica flake the needles are all turned the same way, but the two sets are oppositely directed in order to minimize the effect of the earth's magnetic field. The two sheets of mica are rigidly attached together and to a mirror between the cylinders, and mica and mirror are all suspended by a fine fiber. ("Astatic" refers to the fact that the design minimizes the effect of the earth's magnetic field.) This instrument was purchased from Queen & Company for $30, probably near 1900.

A sensitive galvanometer designed by William Thomson (later Lord Kelvin) in 1858 to detect the current through the Atlantic cable. A small mirror is suspended by a thread between two coils, and on the back of the mirror are glued several short and light magnets. The curved bar over the galvanometer case is a permanent magnet which can be rotated and raised or lowered to minimize the effect of the earth's magnetic field and to center the supension system. The instrument was purchased from Queen & Co. for $30, but the date is not known.

Like many other galvanometers, a ballistic galvanometer has a coil which rotates between magnets. The ballistic galvanometer has the special feature that its rotating coil has a large moment of inertia. It is used to measure quantity of charge rather than currents, for the large moment of inertia permits the passage of a quantity of charge before the coil moves significantly. The passage of the charge produces an impulse, a momentary torque, which causes the coil then to swing slowly to some maximum position. Such a galvanometer was often used to standardize capacitors. This galvanometer was purchased from Queen and Company for $75. probably near 1900.

This instrument almost certainly was on the Grinnell College campus before the tornado of 1882 which destroyed most of the college's scientific equipment. Its manufacturer is unknown. The Bohnenberger electroscope has a dry pile which produces a constant potential difference of the order of 1000 volts. Charge is placed on the electrode extending up from the top, whence it flows to a single sheet of gold leaf hanging between two plates attached to the dry pile. The charge on the gold leaf, hanging in the electrical field produced by the plates attached to a battery, caused deflection of the gold leaf. Because the polarity of the pile was known, the sign of the charge on the electrode and some indication of its magnitude could be seen.

When Frank Almy came to Grinnell College in 1893 to teach physics, laboratory equipment was not as readily available as it was later. Probably the cost of equipment also placed a severe constraint on purchases. Almy made a number of galvanometers, some of which survive. One of those galvanometers is shown here. It had a mirror attached to small magnets suspended between coils.

At the time Frank Almy began teaching physics at Grinnell College in 1893, the tangent galvanometer was an important part of the equipment of any physics laboratory. This is a tangent galvanometer that Professor Almy made. The date is not known, but it probably was before 1900. The compass in the center is a modern instrument; we do not know what compass Professor Almy used.

This is a capacitor with adjustable plates and a plate of glass which can be inserted between the plates. With static charges on the plates, the effects of plate separation and nature of the dielectric between the plates can be studied. This was purchased from Queen & Company, but the date is unknown.

A Kohlrausch wire is a uniform wire wound on a form with a slider which moves along the wire. It can be used as part of a Wheatstone bridge or a potentiometer. This wire was made in Germany and imported by James G. Biddle. Its resistance is 195 ohms. The form is marble.

This is one of several resistors of high quality which are in the museum. Such resistors were used as standards in bridge circuits to measure unknown resistances to high precision. The thermometer is included because the resistance is exactly one ohm only at a specified temperature.

This is a standard capacitor used to calibrate equipment and measure other capacitances.

This is a Wheatstone bridge designed to locate a short circuit in a telephone or telegraph line by measuring the resistance of the wire to the short. It is called a "post office bridge" because this design was adopted by the British Post Office, which operated telegraph and telephone services as well as delivered mail. This bridge, which is in a box, has a built-in galvanometer. The upper plugs determine a ratio and the lower rows are a standard resistance.

The base of this tangent galvanometer is marked "Queen & Co., Makers, Phila." The date of purchase is not known.

This variable standard of self-inductance is graduated in milli-henries.