POTCHEFSTROOM 



Pot chefs troom. Town of the 

 Transvaal, S. Africa. It stands on 

 the Mooi river, at an elevation of 

 4,000 ft., 88 m. by rly. S.W. from 

 Johannesburg. The buildings in- 

 clude an agricultural college, con- 

 nected with an experimental farm, 

 and it is the centre of a fine agri- 

 cultural country. There are gold 

 mines in the neighbourhood. The 

 town has a large park, fine golf 

 links, and a lake formed from the 

 river here. It was founded by a 

 band of wandering Boers under 

 Potgieter in 1839, and was for some 

 time before 1863 the capital of the 

 little Boer republic. In 1862, dur- 

 ing the civil war, it surrendered to 

 Kruger after a comparatively 

 harmless bombardment. In the war 

 of 1880-81, a small British force 

 surrendered here to the Boers, after 

 a stubborn defence. On June 11, 

 1900, Colonel B. T. Mahon entered 

 the town without opposition from 

 the Boers. Pop., whites, 9,600. 



Poteen OR POTHEEN (Irish 

 poitin, little pot). Whisky illicitly 

 distilled by Irish peasantry. The 

 making of poteen arose at the end 

 of the 18th century owing to the 

 government's refusal to license 

 small stills in Ireland, and the 

 smuggling became so general that, 

 in 1815, to discourage illicit dis- 

 tilleries, licences were granted to 

 stills of only 40 gallons' content. 

 Poteen is still occasionally made 

 in remote parts of Ireland. See 

 Pot Still 



Potemkin, GREGOREI ALEXAN- 

 DROVITCH, PRINCE (1739-91). Rus- 

 sian statesman. He was born Sept. 

 27, 1739, near 

 Smolensk, of 

 an ancient 

 Polish family. 

 One of the con- 

 spirators who 

 dethroned 

 Peter III in 

 favour of Cath- 

 erine II, he 

 early attracted 

 the notice of 

 the empress, and in 1762 became a 

 gentleman of the bed-chamber. In 

 the war against Turkey, 1771, he 

 was made lieut. -general. He was 

 responsible for the partition of Po- 

 land and the conquest of the 

 Crimea, 1783, which was accom- 

 panied by the wholesale butchery 

 of some 30,000 Tartars. In 1787 

 he declared war against Turkey, 

 and, as commander of the Russian 

 army, took Ochakov, Dec. 17, 

 1788. He died near Jassy, Oct. 15, 

 1791. Potemkin owed much of his 

 influence with Catherine to his 

 handsome appearance, 1 which 

 earned him the epithet of the 

 Russian Alcibiades. See Memoirs, 

 trans, from the German, 1812. 



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POTENTIOMETER 



Prince Potemkin, 

 Russian statesman 



Potchefstroom, Transvaal. Church Street, the principal thoroughfare 



Potent. In heraldry, a fur re- 

 presented by crutch-like figures of 

 white and blue, placed in rows, the 

 base of the white against the base 

 of a blue. The variants are, counter- 

 potent, in which the bases of one 

 tincture are placed against bases 

 of the same ; and potent-counter- 

 potent, in which the rows are so 

 arranged that the base of a metal 

 figure rests on the centre of a 

 coloured crutch head, and so on 

 alternately. If the tinctures differ 

 from the above the fact should be 

 mentioned. See Cross ; Heraldry, 

 colour plate. 



Potential. Broadly, a term 

 meaning power to do work. What- 

 ever form a particular technical 

 definition of potential may take, 

 it will always include this sense. 

 A steam boiler under pressure, an 

 elevated body of water, a cylinder 

 of compressed gas or ah", all have 

 potential, i.e. power to do work, 

 whenever the necessary conditions 

 are satisfied. The essential factor 

 of these conditions is always a 

 difference, which may be said to be 

 a difference of pressure. Two steam 

 boilers, both at the same pressure, 

 have no potential with regard to 

 one another ; neither can do any 

 work against the other ; but when 

 either is connected to a condenser, 

 or opened up to the atmosphere 

 through a steam engine, it can do 

 work by virtue of the difference of 

 pressures which thus arises. Its 

 potential is measured by these 

 differences of pressure. 



In electricity, the term is used 

 for the work done in charging a 

 body with a positive charge taken 

 from a body in which the electri- 

 cal tension is zero. The earth itself 

 has potential ; it may be positive 

 or negative at any point, but it is 

 something. It is, however, so little 

 that its amount is neglected, and it 

 is regarded as nothing zero po- 

 tential and is the starting-point, 

 therefore, in practical measure- 

 ments of electric potential, pre- 

 cisely as " sea level " is the start- 

 ing-point in the measurement of 

 the heights of mountains. 

 . All practical purposes are served 

 by regarding electric potential as 

 pressure, corresponding precisely 



to the pressure of the steam in a 

 steam boiler ; while it is converted 

 into work by falling from a higher 

 to a lower pressure, which may be 

 zero or something intermediate. 

 Hence it is regarded as potential 

 difference and commonly expressed 

 by the letters P.D. ; while another 

 expression used for it is electro- 

 motive force (E.M.F.). It is mea- 

 sured in volts, which correspond 

 to pounds or atmospheres in the 

 measurement of steam, ah", or gas 

 pressure. Thus, when it is said 

 that the voltage of an incandescent 

 electric lamp is 200, it is meant 

 that a potential difference (P.D.) 

 or electromotive force (E.M.F.) 

 of that pressure or intensity is re- 

 quired to force through the lamp 

 the necessary quantity of electricity 

 to raise the filament to the tempera- 

 ture needed, in order that it may 

 give out its proper measure of light. 

 See Electricity; Unit, Electric. 



Potentiometer. In electricity, 

 an instrument for measuring or 

 comparing the electromotive force 

 (E.M.F.) of a cell, or of a current 

 passing through a resistance. The 

 potentiometer method of ascertain- 

 ing the E.M.F. of a cell has the 

 advantage of doing so when the 

 cell is giving no current, and there- 

 fore developing its full pressure. 



The principle is explained by the 

 diagram, in which X is the cell 

 under test, S a standard Clark or 

 Weston cell, B a battery of greater 

 E.M.F. than either X or S, and 



Potentiometer. Diagram illustrating 

 principles of the instrument. See text 



N P a wire of high resistance with 

 sliders a, b. The cell positive ter- 

 minals are all connected with P 

 (those of S and X alternatively 

 through switch R). Galvanometer 

 G is interposed between R and P. 



