The line was not recognized by any statute of the English Parliament but was usually understood as 1⁄4 of a barleycorn, (which itself was recognized by statute as 1⁄3 of an inch) making it 1⁄12 of an inch, and 1⁄144 of a foot. The line was eventually decimalized as 1⁄10 of an inch, without recourse to barleycorns.
The US button trade uses the same or a similar term but defined as one-fortieth of the US-customary inch (making a button-maker's line equal to 0.635mm (0.0250in)).
In use
Botanists formerly used the unit (usually as 1⁄12 inch) to measure the size of plant parts. Linnaeus's Philosophia botanica (1751) includes the Linea in its summary of units of measurements, defining it as Linea una Mensurae parisinae [lit.'One line of the Parisian measure']; Stearns gives its length as 2.25mm (0.089in). Even after metrication, British botanists continued to employ tools with gradations marked as linea (lines); the British line is approximately 2.1mm (0.083in) and the Paris line approximately 2.3mm (0.091in).
Entomologists in the UK and other European countries in the 1800s used lines as a unit of measurement for insects, at least for the relatively large mantids and phasmids. Examples include Westwood, in the UK, and de Haan in the Netherlands.
Gunsmiths and armament companies also employed the 1⁄10-inch line (the "decimal line"), in part owing to the importance of the German and Russianarms industries. These are now given in terms of millimeters, but the seemingly arbitrary 7.62 mm (0.30 in) caliber was originally understood as a 3-line caliber (as with the 1891 Mosin–Nagant rifle). The 12.7mm (0.50in) caliber used by the M2 Browning machine gun was similarly a 5-line caliber.
Other 'line' units
Other similar small units called lines include:
The Russianliniya (ли́ния), 1⁄10 of the diuym, which had been set precisely equal to an English inch by Peter the Great
The Frenchligne or "Paris line", 1⁄12 of the French inch (French: pouce), 2.256mm and about 1.06 L.
The Portugueselinha, 1⁄12 of the Portuguese inch or 12 "points" (pontos) or 2.29mm
The Germanlinie was usually 1⁄12 of the German inch but sometimes also 1⁄10 German inch
↑2.54, 2.12, 1.59, 0.64 mm, rounded to two decimal places.
References
Citations
↑"Barleycorn". Oxford Dictionary of English (3rded.). Oxford University Press. a former unit of measurement (about a third of an inch) based on the length of a grain of barley
↑The Metric System | Hearings Before a Subcommittee of the Committee on Manufactures, United States Senate, Sixty-seventh Congress, First and Second Sessions on S. 2267 a Bill to Fix the Metric System of Weights and Measures as the Single Standard of Weights and Measures for Certain Uses. By United States. Congress. Senate. Committee on Manufactures. 11 October 1921. p.216.
↑Stearn, W.T. (1992). Botanical Latin: History, grammar, syntax, terminology, and vocabulary (Fourthed.). David and Charles.
↑Westwood, J.O. (1859). Catalogue of the Orthopterous Insects in the Collection of British Museum. Part I: Phasmidae. British Museum, London.
↑Westwood, J.O. (1889). Revisio Insectorum Familiae Mantidarum, speciebus novis aut minus cognitis descriptis et delineatis. – Revisio Mantidarum. Gurney & Jackson, London.
↑Haan, W.de (1842). Bijdragen tot de Kennis Orthoptera. in C.J. Temminck, Verhandelingen over de natuurlijke Geschiedenis der Nederlandsche overzeesche Bezittingen. volume 2.