I always think that engineers should uniformly work in S.I. Units to avoid confusion. These measurement explanations make our present-day measurements look positively uniform, easy and clear.
Let's see. A statute mile, a sea mile, a Scottish mile, an Irish mile, a chain, a perch, an ell, a fall and how about those roods...
Rankine, William John MacQuorn, A Manual of Civil Engineering, Exeter Street, Strand, London, Charles Griffin and Company, 1883.
In addition to the yard, the following units of length are employed for purposes of civil engineering in Britain:--
The Inch, one thirty-sixth part of the standard yard; with binary, decimal, or duodecimal subdivisions.
The Foot, one-third part of the standard yard; with decimal or duodecimal subdivisions.
The Fathom of two yards.
The Chain of 66 feet or 22 yards; divided into four poles of 5 1/2 yards, and 100 links of 7.92 inches.
The Statute Mile of 1,760 yards = 5,280 feet = 80 chains, divided into 8 furlongs. To these may be added, in cases of harbour engineering--
The Nautical or Sea Mile, being the length of one minute of a degree of latitude at the mean level of the sea. The length of this mile varies in different latitudes, from about 6,107 feet at the poles to about 6,045 feet at the equator, its mean value being nearly 6,076 feet, or 1.1508 statute mile. A value commonly taken for the nautical mile is that of a minute of longitude at the equator, or 6086 feet - 1.1527 statute mile. The nautical mile is sometimes subdivided intp 10 cables, and 1,000 fathoms; the fathom thus obtained being, on an average, about 1/80th longer than the common fathom.
The Irish Perch of 7 yards, being greater than the imperial perch in the proportion of 14 to 11.
The Irish Mile of 320 Irish perches = 2,240 yards = 6,720 feet, bearing to the statute mile the same proportion of 14 to 11.
The Scottish Ell of 37.06 imperial inches.
The Scottish Fall of 6 ells, or 18.53 imperial feet.
The Scottish Mile of 1,920 ells = 5929.6 feet.
Each of these miles is divided, like the statute mile, into 8 furlongs, and 80 chains, so that the Irish, Scottish, and imperial mile, furlong, and chain, bear to each other the proportions--
6720 : 5929.6 : 5280
1.27 : 1.123 : 1.000
The French measures of length are all decimal multiples and submultiples of the METRE, which is approximately one ten-millionth part of the distance from one of the earth's poles to the equator. The value of the metre in British measures is
3.2808693 feet, or 39.37043 inches.
For further information of the same kind, see the Comparative Table of French and British Measures at the end of the volume.*
The Measures of Area used in British civil engineering are--
The Square Inch.
The Square Foot of 144 square inches.
The Square Yard of 9 square feet.
The Acre of 10 square chains, or 100,000 square links, or 4,840 square yards, subdivided either decimally, or into 4 roods of 1,210 square yards, and 160 perches of 30 1/4 square yards.
The Square Mile of 640 acres, or 3,097,600 square yards, or 27,878,400 square feet.
The Irish acre, subdivided into 4 roods and 160 perches, and the Scottish acre, subdivided into 4 roods and 160 falls, bear to the imperial acre proportions which are the squares of the proportions borne by the Irish and Scottish miles respectively to the statute mile; that is to say,
Irish acre : Imperial acre : : 196 : 121 ;
Also, Irish acre : Scottish acre : Imperial acre
: : 1.6198 : 1.2612 : 1.0000 nearly.
The Cubic Inch.
The Cubic Foot of 1,728 cubic inches.
The Cubic Yard of 27 cubic feet.
In the engineering of water-works, the Gallon is used in stating quantities of water. Its statutory value is
277.274 cubic inches, or 0.16046 cubic foot;
but it is convenient in calculation, and in general sufficiently accurate for purposes of water supply, to use the approximate values,
One gallon ...= 0.16 cubic foot, nearly; and
One cubic foot= 6 1/4 gallons, nearly.
Other special measures of volume are employed for certain kinds of materials and work; but these will be explained further on.
*Comparative Table of French and British Measures.
