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Glossary: Home Tables A B C D E F G H I J K L M N O P Q R S T Th U V W X Y Z

Earth *
Some numbers relating to the earth, moon and sun. The proportional numbers are against a scale where 1 makes 720 miles BI.
Moon diam Earth diam . do. mean 3 2158.767 mi 2160 11 7899.864 mi 7920 11 7917.511 mi 7920 34.54 24880.615 mi 24872.72 330 238855 mi 237600 1200 864948.7 mi 864000 350000/17 14794377.828 mi 14823529.4 129360 92955817.4 mi 93139200 5.5153 1303.147 gr/in³ 5515.3 kg/m³

The relation of pi given by 17*129360/35e4 is 3.1416 (exact), a value known to the Indians
The relation of 11 to 34.54 gives pi as 380/121 = 3.140495. Note also that the diam of 7900 miles, to the admiralty diam 24872.72 gives pi = 3.148446, or 2736/869.
eimer *
der Eimer = one + bear (carry) = one-handled, eg bucket
der Zuber = two + bear = two-handled, eg tub
Electrodynamic Units*
A gaussian scale where the speed of light is set to unity. This, when taken with Length and Force as units, makes the basic ESU and EMU into coherent units.
Because we have length and time co-dependent, the scale gives rise to a common dimension number, where time = length = 1, mass = 23, and charge = 12. Units that map onto different dimension-numbers are not the same measure.
elephant (weight of)
The weight of an ilp is taken to be 11000 lbs.
Electromagnetic Units *
A scale of electric units, derived by setting the magnetic constant to unity, specifically, UES MU=1.
Since electric measures are measured by the produced magnetic field, the original proposal for the Practical electric units was taken to be a decade multiple of the practical metric units.
The usual implementation is to define current, such that MLTI
The unit I is that, which when folwing through each of two wires of negligable cross section, and distance 1 L appart, produces a force of 2/n F for each length of wire.
System CGSBi MKSA Practical Length Force n Current cm dyne 1 Biot = abampere m newton 1E7 Ampere L joule / L 1e7 m / L Ampere
Because rationalisation takes place after dimensions are applied, the same definition results in CGSBi(r), etc, where 1/n H/m refers to the radial inductivity of free-space.
Electrostatic Units *
A theoretical system, defined by setting the force between unit charges at unit distance to unity.
For this system, one normally writes it as LMTQ, with a derived charge as
One Q is that charge that placed at each of two points separated by L, produces a force of nF.
 System esu CGSFr length force n charge unit [length] [force] 1 esu cm dyne 1 franklin = statcoulomb
Electrosymmetric Unit *
A system derived by setting epsilon = mu = 1/c. The system corresponds to UES rule NR.
An implementation of this or related systems has not been formalised.
Enfield Inch *
A unit that came from problems caused in Pratt and Whitney at Lithgow, being some 0,99966 of an imperial inch. See Tony Griffiths "The Enfield Inch and the Lithgow .303"
Ellipsoid *
The second approximation to the shape of the earth. The earth is taken as a best-fit ellipsoid, with a polar axis different to the Equator.
At one stage, it was thought that the earth was prolate: that the polar axis were longer than the equator, but now the oblate model is known to be the correct shape. The order of flattening is about one in 299.
engineering *
Engineering tends to trail scientific concepts, as it takes time for ideas to filter from design to implementation. The engineering units typically retain notions and units long abandoned by the scientific community.
Engineering units tend to deal in named units rather than systems. The quest for practical electric systems is a result of engineering, rather than scientific endeavour. In some extent, it really does not matter if the unit is coherent, but more if it is understood by the public in general. Horsepower captures the imagination of the general public much better than kilowatt.
Engineering notation tends to follow the larger comma-units. In past, this reflects the use of foot + mile, while skipping the intervening units. The notation tends to follow commas, eg one writes 46,656 as 46.656e3 rather than 4.665 6 E4.
epact *
A device used to find easter, representing the age of the moon on 1 Jan or 1 Mar (Jan + Feb has 59 days = 2 lunar months).
If the age of the moon is 23 on 1 Mar, then a new moon falls on 8 Mar, being 23+7=30. This is day 1, where day 14 makes for 21 Mar, the earliest day for easter. A moon that is one day younger makes the full moon fall one day later.
eotvos *
A unit for measuring rate of change of gravity, being 1e-9 cm/s/s per horizontal centimetre. This corresponds to 7.46496 per day squared.
The typical range of gradient change is in the order of 5 to 50 eotvos, which corresponds to 118 */ 3.1 of days².
epact Shift *
The effect of an epact shift is to make the moon one day younger in the year of correction. This reduces calculated epact by one, and causes the 19 golden days to cycle through the 30 lunae or epacts.
An epact shift is worth 19 Australs. At this time, 9 such corrections, amounting to 171 australs, have been effected.