Jirou Hemmi and Co. was founded April 15, 1895 but no Hemmi slide rules from before about 1913 are known. Hemmi was granted Japanese patent 22129 in 1912 for laminated bamboo construction and success seems to have followed quickly thereafter. Tamaya and Co. in Tokyo started selling Hemmi slide rules in 1913 as did the Hughes-Owens company of Canada in 1914. The Frederick Post Company of Chicago began selling Hemmi slide rules in 1931.
One can estimate dates of Hemmi slide rules
from markings on the rules.
|Before 1928||Signed “J. Hemmi,” not “Hemmi.”|
|1927/32||Hemmi introduced a new model numbering system between 1927 and 1932. (I have not been able to narrow the date.) Rules with model numbers 1-18 date from before this changeover, rules with model numbers 20 and above were made after the changeover. EXCEPTIONS: Hemmi continued offering models 1, 5 and 8 to its distributors until WWII or later; these rules occasionally turn up with Post or Hughes-Owens model numbers but no Hemmi model number.|
Brand name is “Hemmi” (not
“J. Hemmi”) and “SUN” is in quotation marks.
The company name was officially changed from "J. Hemmi and Co" to "Hemmi Seisakusho & Co." (Hemmi Engineering Works Co.) in 1928 but company was referred to as "Hemmi Seisakusho" at least as early as 1917. Hemmi was incorporated as a public corporation 1933 with no change in name.
|1937-40?||The first inch or first five centimeters of the measuring scales on ten-inch closed body rules is extra-finely divided. Although discontinued about WWII on ten inch rules; a short section of extra fine divisions continued until the end of production on models 86K and 86/3K.|
No quotes around SUN, marked
“Made in Occupied Japan.”
Name changed to "Hemmi Keisanjaku
Co." (Hemmi Slide Rule Co.) in 1946. Hemmi continued to operate
under that name through at least 2015.
The Allied Powers occupation of Japan
lasted from August 1945 until April 28, 1952 but the requirement that
export goods be marked "Made in Occupied Japan" was in effect for a shorter
period--from 20 February 1947 to 5 December 1949. (Thanks to Wataru
Tsuchihira who found the original orders in the Japanese National Library.)
|WWII-1955||From WWII until 1955, Hemmi "Mannheim" slide rule models 30, 32, 34R, 34RK, 50 and 50W had S (sine) scales that ran from 5o44' to 90o and were keyed to the C and D scales. Note the S scale on the upper slide in the illustration. Before WWII and after 1955 the S scale ran from 34' to 90o and was keyed to the A and B scales. The S scale on the lower slide in the illustration is an example. Both slides are from Hemmi model 50W slide rules; the upper from a rule dated September 1952; the lower from a 50W dated May 1965.|
|1950-1952||No quotes around SUN, no date code.|
There is a small date code
in the form “YM” engraved into each slide rule but often not colored.
That can make it difficult to find. Often it is in the lower left
of the rear of the rule but can appear almost anywhere. It sometimes
takes inspection with a magnifier in raking light to find the code.
First letter of the date code indicates the year of manufacture with A = 1950. Second letter indicates month with A = January. Thus “BB” indicates February 1951. All-plastic rules use the same date codes preceded by “^” so that the date code looks like “^YM.”
“A” date codes are rare; I know of only two rules so marked. (Both are model 86/3K rules marked "AL" (Dec 1950)). Most rules from 1950-52 escaped dating. The latest date code I'm aware of is "ZB" (Feb 1975) on a Hemmi 254WN owned by Warren Salomon.The date codes reveal the date of most post-1950 Hemmi slide rules but it is not absolutely reliable. Some Hemmi slide rules that clearly should have date codes, don’t. A very few have two different date code.
Ted Hume and I were the original decypherers of the Hemmi date code system; we published it in the Fall 2000 issue of Journal of The Oughtred Society.
|1973-1975||The date coding system ran out with “Z” in 1975. Application of date codes seems to have been erratic for a few years before then; "X," "Y," or "Z" date code are often missing. Hemmi stopped making slide rules about 1975.|
|4/15/1895||"Hemmi Jirou & Co." founded. Rules were marked "J. Hemmi" or "Tamaya" (Hemmi's first retailer).|
|5/11/12||Japanese Patent 22129 for laminated bamboo construction.|
|1917||British Patent 107562 for laminated bamboo construction.|
|4/5/20||Japanese Pat. 51788 for method of attaching glass to cursor. Initially used on metal-framed cursors; later on frameless ("Type B"). (Date thanks to Clay Castleberry and Atsushi Tomozawa.)|
|2/3/20||US Patent 1329902 for laminated bamboo construction.|
|ca 1921||Japanese Patent 58115 ("Type A" cursor).|
|1921||US import marking requirement changes from "Japan" to "Made in Japan" (but not consistently enforced until ca 1925).|
|1925||Pythagorean scales, P & Q introduced.|
|ca 1927||Model numbering system revised. Models 1-18 dissapear; model numbers above 20 introduced.|
|1928||Company renamed "Hemmi Seisakusho & Co." (Hemmi Engineering Works & Co.) Rules are marked just "Hemmi," no longer "J. Hemmi."|
|1929-45||"SUN" in quotes.|
|1931||Gudermanian scale, Gtheta, introduced.|
|5/4/37||US Patent 2079464 for Gudermanian/hyperbolic scale.|
|1946||Company renamed "Hemmi Keisanjaku Co." (Hemmi Slide Rule Co.)|
|1947-49||Rules made for export are marked "Made in Occupied Japan."|
|1950||Date codes introduced.|
Cursor B is unpolished soft aluminum. The plain version (non magnifying, non decimal-indicating) appears only in the 1913 Tamaya catalog. Magnifiying and decimal-indicating versions (but not plain versions) appear in the 1914 Hughes-Owens and the 1919 Tamaya catalogs.
Cursor C is unpolished soft aluminum and essentially identical to B except that the frame around the glass is narrower and the inside frame corners are not rounded. The plain version first appeared in the 1914 Hughes Owens catalog and magnifying and decimal-indicating versions first appeared in the 1919 Tamaya catalog (in which some rules were still shown with magnifying and decimal-indicating versions of cursor B). Available in standard, magnifying, decimal-indicating, and magnifying-decimal-indicating versions.
Cursor D is the "decimal-indicating" variant
of C. Hemmi's 1912 patent application shows this style cursor.
Cursor B is "frameless" glass, also patent 51788. ("Made in Japan" has been removed from the specimen shown.) Hemmi referred to it as the "Type B" cursor. It first appeared in the 1926 Hemmi catalog and had vanished from Hemmi material by 1936. A magnifying version was available.
Cursor C is Hemmi's famous "Type A"--patent 58115--cursor. Construction is polished aluminum. Available in standard, magnifying, decimal-indicating, and magnifying-decimal-indicating versions. Type A was Hemmi's top of the line cursor from 1925 to WWII.
An interesting variant of the type A cursor is the "extended magnifying lens" cursor from 1926-27. None is known to have survived.
Illustration C shows Hemmi's Improved
Type A cursor with a narrow chrome-plated frame. This improved
type A cursor was introduced about 1934 on Hemmi's less sophisticated
rules and gradually supplanted the type A cursor on other rules, completely
replacing it around WWII. Dates: 1934-end of production.
Hemmi re-introduced all-plastic cursors
on its less sophisticated rules in the 1960s. There is a wide variety,
ranging from small cursors with high magnification to elaborate, multi-line
cursors. These cursors are too varied to be described by any
general principles but their slide rules usually carry date codes.
All Hemmi five-inch bamboo duplex rules use chrome-framed glass cursors like this.
Hemmi plastic duplex slide
rules used all-plastic cursors like those shown in the illustration
at right. The design on the left was used on extra-thick (about
5mm) duplex rules. The design on the right was used on thinner