Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/700

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.—A most excellent account of the units employed in scientific measurements will be found in Professor J. D. Everett's Units and Physical Constants, London, 1879. We shall here only give a very brief out line of this branch of the general theory of measurement, referring inquirers to Everett's volume for further details. Most of the quantities for which measurements are needed can be ultimately expressed by means of (1)a definite length, (2)a definite mass, or (3)a definite interval of time. It is very important that the units thus referred to should be chosen judiciously, and it must be admitted that the units ordinarily used do not fulfil the conditions which a well-chosen system of units should fulfil. The most scientific system is beyond doubt that which has been suggested by the units committee of the British Association. In this system the unit of length is the centimetre, the unit of mass is the gramme, and the unit of time is the second, and the system is therefore often referred to for brevity as the C.G.S. system. The unit of force is termed the dyne, and it is defined to be the force which, acting upon a gramme of matter for a second, generates a velocity of a centimetre per second. The unit of work is the work done by this force working through a centimetre, and this unit is termed the erg. The unit of power is the power of doing work at the rate of one erg per second, and the power of an engine can be specified in ergs per second. By the prefixes deca, hecto, kilo, mega, we can express a magnitude equal to the unit multiplied by 10, 100, 1000, or 1,000,000 respectively. On the other hand the prefixes deci, centi, milli, micro, signify the units divided by 10, 100, 1000, or 1,000,000 respectively. For comparison with the ordinary units the following statements will be useful. The weight of a gramme at any part of the earth's surface is about 980 dynes, or rather less than a kilodyne. The weight of a kilogramme is rather less than a megadyne, being about 980,000 dynes.

1em (Author:Robert Stawell Ball)  MEATH, a maritime county of Ireland, in the province of Leinster, is bounded E. by the Irish Sea, S.E. by Dublin, S. by Kildare and King s county, W. by West- meath, 1ST. W. by Cavan and Monaghan, and N.E. by Louth. Its greatest length north and south is about 40 miles, and its breadth east and west about 45 miles. The total area comprises 578,247 acres, or 904 square miles. The county forms part of the great limestone plain that occupies the central portion of Ireland. In some districts the surface is variegated by hills and swells, which to the west reach a considerable elevation, although the general features of a fine champaign country are never lost. The coast, which is low and shelving, extends to about 10 miles, but there is no harbour of importance. The Boyne, whose banks are specially beautiful, enters the county at its south-west extremity, and flowing north-east to Drogheda divides it into two almost equal parts. At Navan it receives the Blackwater, which flows south-west from Cavan. The Boyne is navigable for barges as far as Navan, where a canal is carried to Trim. The Eoyal Canal passes along the southern boundary of the county to Dublin. There are no lakes of importance.

Climate and Agriculture.—The climate is genial and favourable for all kinds of crops, there being less rain than even in the neighbouring counties. The principal substratum is limestone, but there are some districts of clay slate. Except a small portion occupied by the Bog of Allen, the county is very verdant and fertile. The soil is principally a rich deep loam resting on limestone gravel, but varies from a strong clayey loam to a light sandy gravel.

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Wheat. 18,764 2,783 Oats. Other Cereals. Potatoes. Turnips. Other Green Crops. Flax. Meadow and Clover. Total. 1855 1882 8(5,831 31,202 4.876 1,577 19,235 12,071 9,904 6,724 4,005 3,109 26(5 59 64,646 82,572 208.527 140,097

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