537 items

Jolly Balance

A Jolly balance has a weak spring so that it stretches a great distance when a small force is applied. If a small, known force was applied to the pan and the resulting extension of the spring noted, the spring constant could be calculated and the balance then used to measure other small forces. The name comes not from the attitude of its users but from the name of its 19th century inventor

Magdeburg Hemispheres

In 1654, Otto von Guericke, burgomaster of Magdeburg, performed an experiment using two brass hemispheres which fit together closely to make a sphere and which could be evacuated with a vacuum pump, which von Guericke had invented in 1650. Von Guericke used hemispheres about fourteen inches in diameter, and when as much air as possible had been pumped from them, two teams of horses could not pull the hemispheres apart. The hemispheres shown here were purchased for $6.00 in 1885. __________________________________________ Mayor Otto von Guericke of Magdeburg (1602-1686 AD) clearly had a flair for the dramatic. His scientific demonstrations involved props such as guillotines and strongmen. But his most famous public experiment at Regensburg sometime around 1654 (the exact date is uncertain) included what came to be known as the Magdeburg hemispheres. Made of copper or brass, the hemispheres can be joined to form a hollow globe. Using an air pump (which von Guericke also invented), he removed the air from the sphere and showed how 16 horses – 2 teams of 8 each – could not pull the halves apart. The sphere immediately fell apart once air was reintroduced. From this experiment, he showed that the air pressure surrounding the hemispheres, without the counteraction of the pressure normally existing inside the sphere when it was filled with air, made them cling together. Scientists were just beginning to realize that we live under an ocean of air, with the mass of the atmosphere corresponding to a pressure of about 1 kg per cm2. The discovery of the sheer force of the pressure of the atmosphere led to the development of the first steam engines in the 1700s. Although the 1600s were a tumultuous time in Magdeburg’s history, von Guericke still found time to contemplate various questions about the nature of space. Aristotle (384-322 BC) proposed that “nature abhors a vacuum,” currently defined as any volume with a lower particle density and gas pressure than the surrounding atmosphere. This postulate would be believed for almost 2000 years. Evangelista Torricelli (1608-1647 AD), one of von Guericke’s contemporaries, demonstrated in 1643 that a vacuum could exist in space above an enclosed column of mercury. However, from astronomical observation of the constancy of the time it took for planets to revolve, von Guericke concluded that space is also a vacuum without friction. He also conducted experiments on the elasticity of air, as well as the relation of air pressure and altitude. Combined with Blaise Pascal’s discovery of the link between atmospheric pressure and weather, von Guericke proposed meteorological stations to gather data to forecast the weather. Other discoveries he is credited with include the magnetization of iron, the invention of a static electricity generator, and the observation of colored shadows. -Mira Lamb 2018 References “Guericke, Otto Von,” accessed April 14, 2017. guericke-otto-von/m0091124. Marquardt, Niels. “Introduction to the principles of vacuum phsyics,” last modified November 22, 2016.

Nicholson's Hydrometer

The Nicholson hydrometer is used to determine the specific gravity of a material more dense than water. The conical cup at the bottom should have enough lead in it that the cylinder floats upright in the water. An index mark is made on the the floating tube above the water level. Then three measurements are made: (1) weights are added to the top pan to press the float down to the index mark; (2) the substance whose density is desired is placed in the top pan and weights are added to depress the float to the index mark again; (3) the substance being examined is placed in the bottom pan and again weights are added to the top pan to bring the float to the index mark. From the values of the weights added in the three conditions the density of the substance can be computed.

Vacuum Pump and Bell Jar

This vacuum pump (hand operated by a handle now missing) was made by Jas. W. Queen & Co. and purchased in 1885 for $25. _________________________________________ In 1654, Otto von Guericke was credited for inventing the first Vacuum pump. It was not until 1660 that Robert Boyle published his New Experiments in which he describes his theory of air pressure (Brush, 13). His theory would then become known as Boyle’s Law in which the volume and absolute pressure of a contained gas are inversely proportional. Until the 17th century, air was an invisible substance that could not be studied or explained. With the invention of the Vacuum pump, the principles of air could not only be studied, but they could be demonstrated in such a way that was ultimately undeniable (Brundtland, 265). This type of demonstration not only depicted scientific discovery, but also commanded a certain amount of excitement. Well into the late 1700’s and early 1800’s, experiments continued in the realms of sound, electricity, and mechanics (Brundtland, 267). Grinnell College bought a vacuum pump in 1885 for 25$ from a fairly well known manufacturer of scientific instruments known as Queen & co. This pump is a single barrel pump with a standard sealable bell jar. Air can be evacuated from the jar by pumping the handle (now missing) up and down. -Jordan Hamilton 2019 References Brundtland, T. "Francis Hauksbee and His Air Pump." Notes and Records of the Royal Society 66.3 (2012): 253-72. JSTOR. Web. Brush, Stephen G. "Gadflies And Geniuses In The History Of Gas Theory." History of Modern Physical Sciences The Kinetic Theory of Gases (2003): 421-50. JSTOR. Web.

Nicol Prisms

A Nicol Prism is a device to produce polarized light. It is made from a crystal of calcite, which is cut along a precisely determined plane and then cemented back together with Canada balsam. When a beam of light enters the crystal along the line defined by the mounting of the crystal, it is broken into two beams. In the two beams the planes of vibration of the electric field vector are perpendicular to one another. When the two beams strike the cemented cut, one is passed through and the other is deflected to the side and absorbed in the mounting.


This is the first laser owned and used by the Grinnell College Physics Department. It is a helium-neon laser, and the gas inside the tube was excited by a radio-frequency field produced by an oscillator. This laser was purchased by Bob Noyce, who experimented with it for a short time and then brought it, carried on his lap on the airplane, to Grinnell and presented it to the Physics Department. The orange plastic cover is lying behind the instrument.

Lens on Stand

This lens on a ball mount has been used for many years for lecture demonstrations. Although neither date of purchase nor maker is known, it certainly has been part of the college's equipment since the early 1900s if not earlier.

Prism with Variable Angle

This prism with variable angle was used to study how the angle of deviation of a beam of light increases with the refracting angle of the prism. The glass plates which make up part of the prism can move about their hinged bottom edge. Water is placed in the prism, a beam of light is directed through it, and then the angle of the prism can be changed by sliding the glass between the brass sides.

Four Tuning Forks

These four tuning forks, mounted in resonating boxes, were made by L. Landry in Paris. They were purchased in 1900 and the price of the set was $32.


The sonometer is an apparatus by which the transverse vibrations of strings can be studied. It is also called the monocord because it often has only one string. On the box are two fixed bridges, near the ends, and at one end is a pulley. A string, often a steel wire, is fastened at one end, run over the bridges and the pulley, and attached to a weight holder hanging below the pulley. Weights can be added to the holder to produce tension in the wire, and a third, movable bridge, can be placed under it to change the length of the vibrating section of the string. This instrument was purchased from Queen & Co. The date is not known with certainty, but it probably was 1905 or earlier.

Helmholtz Resonators

Before the advent of electronic spectrum analyzers, Helmholtz Resonators were used to detect different frequencies in a sound wave. This set of nineteen resonators was purchased for $70.

Savart Bell and Resonator

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.

Almy's X-Ray Tube

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

Almy's X-Ray Photograph of Keys and Coins

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

Almy's X-Ray Photograph of Frog

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

Almy's X-Ray Photograph of Hand

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.

Ulysse Nadin Chronometer

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.

Solar Microscope

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.

Early Phonograph

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

Kelvin's Astatic Galvanometer

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.

Thomson's Mirror Galvanometer

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.