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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

Some numbers relating to the earth, moon and sun. The proportional numbers are against a scale where 1 makes 720 miles BI.

Moon diam	3	2158.767 mi	2160
Earth diam	11	7899.864 mi	7920
. do. mean	11	7917.511 mi	7920
Earth circ	34.54	24880.615 mi	24872.72
Moon orbit	330	238855 mi	237600
Sun diam	1200	864948.7 mi	864000
parcircle	350000/17	14794377.828 mi	14823529.4
Earth orbit	129360	92955817.4 mi	93139200
Earth dens.	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
see also amphora.

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.

gamma	1	radial admittance
epsilon	1/c²	permittivity
mu	1	permeability
kappa	1	electromagnetic linkage
charge²	Q	ML

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	Length	Force	n	Current
CGSBi	cm	dyne	1	Biot = abampere
MKSA	m	newton	1E7	Ampere
Practical	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.

gamma	1	radial admittance
epsilon	1	permittivity
mu	1/c²	permeability
kappa	1	electromagnetic linkage
charge²	Q	ML3/T2

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	length	force	n	charge unit
esu	[length]	[force]	1	esu
CGSFr	cm	dyne	1	franklin = statcoulomb

Electrosymmetric Unit *

A system derived by setting epsilon = mu = 1/c. The system corresponds to UES rule NR.

gamma	1	radial admittance
epsilon	1/c	permittivity
mu	1/c	permeability
kappa	1	electromagnetic linkage
charge²	Q	ML2/T

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.
See also golden jump, austral

EPS - Electric-Practical System *

Any of a number of systems that include the Volt-Ohm-second electrical units as a substrate. See also practical electric units.

ETU - Electro-technical Units *

A foot-based Practical System.

inch	ton	3600 lb	3417.171 898 209 4 lb	1.550 003 100 006 t
6 in	cwt	100 lb	94.921 441 616 927 lb	43.055 641 666 838 kg
foot	qtr, hile	25 lb	23.730 360 040 232 lb	10.763 910 416 710 kg
pace	baros	4 lb	3.796 857 664 677 lb	1.722 225 666 673 kg
5 ft	pound	1 lb	0.949 214 416 169 lb	430.556 416 668 388 g
20 ft	ounce	1/16 lb	415.281 307 074 06 gr	26.909 776 041 774 g
400 ft	grain	1/6400 lb	1.038 203 267 685 gr	67.274 440 104 435 mg

Egyptian fractions *

A system of fractions given in the form of sum of inverses. I can not see at this time how such might arise, but it is one of the five ancient fraction systems.
The Egyptians became very adept at dealing with these, and in some ways, it is easier to use than other fraction-systems.
Gillings discusses it in his 1972 book.