Emile Alluard, professor of physics at the University of Clermont-Ferand and director of the meteorological observatory on the nearby Puy-de-Dôme, described this type of hygrometer in 1878. A modification of Regnault's instrument, it consists of a square vessel made of polished nickel-plated brass. At either side of the vessel, but not touching it, are strips of similar material. In use, the vessel would be filled with ether, and this ether would be cooled by evaporation by means of an aspirating bulb. When dew appears on the shiny surface of the vessel, a thermometer in the vessel indicates the temperature of the ether at that point. A second thermometer measures the ambient temperature.
Robert A. Millikan described the Alluard hygrometer as being one of the "most perfect forms of the dew-point hygrometer" in his Mechanics, Molecular Physics and Heat, a popular college text that was first published in 1903 and that aimed "to present Physics as a science of exact measurement." This example is marked "A Sign of Quality WELCH A Mark of Service / W. M. Welch Scientific Company / ESTABLISHED 1880 / 1515 SEDGWICK ST. CHICAGO, U.S.A." It was made between 1921 (when the W. M. Welch Scientific Company began as such) and 1960 (when it became Welch Scientific). It is missing the aspirating bulb and both thermometers.
Ref: M. Allouard, "Nouvel Hygromètre a Condensation," Journal de Physique et le Radium 7 (1878): 328-330.
W. M. Welch Scientific Co., Catalog G (Chicago, 1935), p. 157.
In the late 19th century, the Russian chemist Dimitry Ivanovich Mendeleev developed several charts in which chemical elements were grouped according to common properties. The atomic theory of matter developed over the next century suggested that these groupings could be explained by similarities in atomic structure.
In 1924, Henry D. Hubbard of the U.S. National Bureau of Standards prepared the first edition of this "Periodic Chart of the Atoms." It included symbols for the elements, atomic numbers, atomic weights, and descriptions of atomic structure. In the course of the twentieth century, numerous new elements were discovered and added to the chart. Physical data on the properties of elements also was incorporated. Wall charts became a fixture of the chemistry classroom.
The Periodic Chart of the Atoms was revised regularly by the NBS and published by the W. M. Welch Science Company of Chicago. This is the 1963 version of the chart, as prepared by spectroscopist William F. Meggars. High schools could purchase the charts with aid from the U.S. government. Some chemists working on curriculum projects of the time also prepared new forms of the periodic table.
overall: 2 1/4 in x 7 7/8 in x 7 1/4 in; 5.715 cm x 20.0025 cm x 18.415 cm
United States: Illinois, Chicago
Measuring & Mapping
Short discussions of the sextant began appearing in physics texts in the 1880s, and inexpensive sextants suitable for pedagogical purposes followed soon thereafter. This die-cast metal instrument is of that sort. Welch catalogs describe it as a "convenient demonstration model of an engineer’s or a mariner’s sextant." The scale is graduated every 30' from 0° to 120° and read by vernier to six minutes of arc. A small bubble level is mounted on the sighting tube. The inscription reads "W. M. WELCH SCIENTIFIC COMPANY (/) WELCH (/) ESTABLISHED 1880 (/) 1515 SEDGWICK ST. CHICAGO. U.S.A."
Ref: W. M. Welch Scientific Company, Catalog. Scientific Apparatus (Chicago, 1929-1963).
W. M. Welch Scientific Company, "Instructions for the Use of No. 3536 Sextant Model."