J. J. Hicks Pilot Balloon Slide Rule

This wooden instrument is faced on both sides with white celluloid that is attached with brass screws instead of glue. On one side are 20-inch scales: cosine and sine scales on the upper part of the base, two identical logarithmic scales (in three cycles) labeled TIME SCALE on the slide, and a tangent scale on the lower part of the base. The slide is in two pieces, so the second Time Scale may be removed and adjusted relative to the first Time Scale with the aid of a brass thumbscrew.

Three glass indicators are in three-sided brass frames, two on the upper part of the base and one on the lower part of the base. The top of the base is marked: J. HICKS (/) LONDON. It is also marked: PILOT BALLOON SLIDE RULE MO (O is superimposed on M) 505. MO is an abbreviation for Meteorological Office, and 505 may be a serial number. An inventory sticker on the back reads: DEPARTMENT OF AGRICULTURE (/) US. The inventory number has been cut away. The instrument fits in a wooden case covered with black leather and lined on one side with purple satin.

In the 20th century, the Meteorological Office of Great Britain used pilot balloon slide rules to convert azimuth and elevation readings (taken with theodolites during the ascent of a pilot balloon) into data on wind velocity and direction. James Joseph Hicks (1825–1916), who began supplying instruments to the Office in 1869, made the first pilot balloon slide rule in 1915 from a design by Francis John Welsh Whipple, the Superintendent of Instruments.

After Hicks died, W. F. Stanley & Co. took over manufacture of this rule, called the Mark I, but retained the Hicks name. Additional labels were placed on the scales, such as "Azimuth." By 1927, A. G. Thornton Ltd. and other firms were making the Mark II, which had one slide and four indicators. Production of the Mark I may have continued until 1938.

The U.S. Weather Bureau was a part of the U.S. Department of Agriculture until 1940, when it was transferred to the U.S. Department of Commerce. This instrument apparently was not adopted by American meteorologists, since the Bureau used the Keuffel & Esser polyphase duplex slide rule to convert observations. For examples of that type of slide rule, see MA.318476, MA.321778, and 1981.0933.03. For an American theodolite used to observe pilot balloons, see PH.308184.

References: Martin Brenner, "Pilot Balloon Slide Rules," http://www.csulb.edu/~mbrenner/slide.htm; Malcolm Walker, History of the Meteorological Office (Cambridge: Cambridge University Press, 2012), 220; W. R. Gregg et al., Instructions for Aerological Observers, U.S. Department of Agriculture, Weather Bureau (Washington, D.C.: Government Printing Office, 1921), 78; Deborah J. Warner, "Altitude and Azimuth Instrument," National Museum of American History Physical Sciences Collection: Surveying and Geodesy , http://americanhistory.si.edu/collections/surveying/object.cfm?recordnumber=747475.

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