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Robert A. Millikan looking through microscope, ca. 1928. Photo by Eyre Powell Press Service. Photo ID 1.22-8

 

Caltech

 

Scientific Instruments Ancient and ModerN Part III
Celebrating 25 Years of The Caltech Archives 1968–1993

Cambridge and Paul galvanometer

imageThe Cambridge and Paul Instrument Company (originally the Cambridge Scientific Instrument Company) was founded in 1881 by Horace Darwin, Charles Darwin's youngest son, to supply the laboratories of Cambridge University. The Darwin family association with the company continued until the 1970s.

The galvanometer was purchased for Caltech's freshman physics lab in the fall of 1921. It is a Paschen type —designed by the German spectroscopist Friedrich Paschen, based on the Thomson astatic galvanometer.

William Thomson, Lord Kelvin (1824-1907)

imageBorn in Belfast and raised in Glasgow, Thomson attended Cambridge University but returned to Scotland when he was appointed to Glasgow University's chair of natural philosophy at the tender age of twenty-two. Widely known as a mathematician, physicist and inventor, he was ennobled for his services to the British Empire in the field of navigation and the laying of the Atlantic telegraph cable. Following the spread of electric power in the 1880s, his numerous accurate and convenient measuring instruments were marketed worldwide through an elaborate system of patents and partnerships.

Glasgow College in the 18th century

imageView from Glasgow High Street facing east. Lord Kelvin's laboratory occupied the wing between the two quadrangles, adjacent to the tower —a building dating from 1656. This was the first teaching laboratory in Britain. Kelvin's father, James Thomson, occupied the chair of mathematics here beginning in 1831.

Kelvin and James White, Ltd Multicelluar electrostatic voltmeter

imageJames White was the sole maker of many of Lord Kelvin's seventy patents. He established his business in 1849 with Kelvin's financial backing and soon could call himself "Philosophical Instrument Maker to the University" —a title formerly held by James Watt, inventor of the steam engine. White died in 1884, but his Glasgow firm prospered into the 1960s.

The Kelvin and White voltmeter, purchased for Caltech's Bridge Laboratory of Physics, could have been used for standardizing purposes, for meaurement of direct and alternating currents, as well as for measurement of potential differences.

Hilger spectrograph

imageThis instrument, a quartz spectrograph, was manufactured by the British firm of Adam Hilger, Ltd., and was used by Caltech spectroscopists in the Chemistry Division in the 1930s.

Light is passed through or emitted from a chemical substance and enters the apparatus through a slit in the tube. It then undergoes refraction by means of a quartz prism. The resulting spectra are recorded on the photographic plates placed in the wooden housing. Such instruments were widely used for a variety of purposes by both Caltech chemists and physicists.

Robert A. Millikan (1868-1953)

imageMillikan became interested in cosmic rays following his World War I work in meteorology. His earliest measuring devices were small, visually read electroscopes —also called ionization chambers —built in the Caltech physics shop in the early twenties.

Cosmic-ray electroscope

imageElectroscope of cosmic-ray apparatus used by Millikan and Ira Bowen in 1932. By this time Millikan and Arthur Compton were locked in a much-publicized debate over the nature of cosmic rays —whether they were photons, as Millikan claimed, or charged particles, which was Compton's view. Compton would be proved correct.

Millikan, Pearson and Bowen

imageWhen Robert Millikan came to Caltech, he brought with him from the University of Chicago a first-class instrument maker named Julius Pearson (center in photo), as well as his research assistant Ira ('Ike') Bowen (right in photo). Starting in 1921, Millikan designed and had Pearson build in the Caltech physics shop a series of instruments to be used in his cosmic-ray investigations of the 1920s and 1930s.

Small cosmic-ray electroscope

imageThis small electroscope was sent aloft by a hydrogen-filled balloon by Millikan and Bowen from a Texas airfield in 1922. Its job was to measure the levels of ionizing radiation at different altitudes. This was accomplished by photographically recording the deflection of two electrically charged quartz fibers within the chamber as the air around them became increasingly ionized during the balloon's ascent through the atmosphere. The whole apparatus weighed approximately seven ounces.

Millikan's compass

imageCompass used by Robert Millikan in his cosmic-ray work.

Concave grating

imageUsed by Robert Millikan and Ira Bowen in spectroscopic studies. This grating is inscribed with the instrument makers' names. The plate was prepared by the John A. Brashear Company of Allegheny, Pennsylvania, in 1901. It was ruled by Caltech astronomer John Anderson on Henry Rowland's engine at Johns Hopkins University. The plate is made of speculum metal, to which a light aluminum coating was later applied. Millikan and Bowen began their spectroscopy work in Chicago in 1919 and subsequently transferred it to Caltech. The grating was used with a twenty-one-foot hot spark vacuum spectrometer in Room 1 in Bridge Laboratory until 1952.

Photo negative of a diffraction grating

imageRuled by Lewis M. Rutherfurd, dated April 1873. Rutherfurd was an American lawyer and amateur astronomer with an interest in spectroscopy. Prior to his efforts, most spectrum analysis was done on prismatic spectra. Beginning in the 1860s, Rutherfurd pioneered diffraction gratings more accurate than those of his German rival, Friedrich Norbert. Rutherfurd invented a ruling engine which would incise evenly spaced lines on glass or metal by means of a carefully made screw. This "scratching machine" eventually produced gratings up to 1.7 inches, with up to 17,296 lines per inch. Rutherfurd's gratings remained unsurpassed until the work of Henry A. Rowland in the 1880s.

Some of Rutherfurd's gratings were photographed by John M. Blake. The resulting negatives, reported Blake in the American Journal of Science in 1874, produced even more brilliant spectra than the original rulings. However, the photographs had the unexpected defect of producing a series of spurious bands in part of the spectrum.

High-pressure electroscope

imageHigh-pressure electroscope (30 atmospheres) with eyepiece, used more than any other by Millikan in his underwater cosmic-ray experiments. The instrument was made in Caltech's physics shop around 1929 and was used to calibrate other instruments for many years.

This Exhibit and above text are the work of Senior Archivist Charlotte Erwin.

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