P E L P E M 481 cooling of the junctions in a heterogeneous circuit of metals according to the direction in which an electric current is made to pass round the circuit (1834). This reversible effect is proportional directly to the strength of the current, not to its square, as is the irreversible genera tion of heat clue to resistance in all parts of the circuit. It is found that, if a current pass from an external source through a circuit of two metals, it cools one junction and heats the other. It cools the junction if it be in the same direction as the thermo-electric current which would be caused by directly heating that junction. In other Avords, the passage of a current from an external source produces in the junctions of the circuit a distribution of temperature which leads to the weakening of the current by the superposition of a thermo-electric current running in the opposite direction. The true importance of this so-called "Peltier effect" in the explanation of thermo electric currents was first clearly pointed out by Joule ; and Sir W. Thomson (see vol. viii. p. 97) further extended the subject by showing, both theoretically and experimentally, that there is something closely analogous to the Peltier effect when the heterogeneity is due, not to difference of quality of matter, but to difference of temperature in contiguous portions of the same material. Shortly after Peltier s discovery was published, Lenz effected by means of it the freezing of small quantities of water by the cold developed in a bismuth-antimony junction when a voltaic current was passed through the metals in the order named. Peltier s other papers, which are numerous, are devoted in great part to atmospheric electricity, waterspouts, cyanometry and polarization of sky-light, the temperature of water in the spheroidal state, and the boiling-point at great elevations. There are also a few devoted to curious points of natural history. But his name will always be associated with the thermal effects at junctions in a voltaic circuit, a discovery of importance quite comparable with those of Seebeck and Gumming. PELUSIUM, an ancient city of Egypt, at the mouth of the most easterly (Pelusiac) branch of the Nile, was the key of the land towards Syria and a strong fortress, which, from the Persian invasion at least, played a great part in all wars between Egypt and the East. It has not, however, been satisfactorily identified with any place mentioned in the hieroglyphic monuments, and the conjecture of Jerome, who supposes it to be the Sin of Ezekiel xxx. 15, 16, though admirably suited to the context and certainly preferable to the Sais of the LXX., cannot be positively established, Pelusium is the Farama of the Arabs ; the neighbouring place still called Tina is hardly to be identified etymologically with Sin. The country about Pelusium was noted for the production of flax ; the fame of the Pelusian linen is, perhaps, still preserved in the word " blouse." The whole district has now relapsed into sand and marsh, and the site has not yielded any important remains. PEMBERTON, an urban sanitary district of Lanca shire, England, situated on the Lancashire and Yorkshire Railway, 2| miles west from Wigan. Near the town are stone quarries and collieries, and the town itself possesses cotton -mills, chemical works, and iron-foundries. At a short distance is Hawkley Hall, an ancient timber house. At Ancliff in the township of Pemberton there was, accord ing to ancient records, a burning well of considerable fame, but the name Ancliff has now disappeared, and the site cannot be verified. The population of the urban sanitary district (area 2894 acres) in 1871 was 10,374, and in 1881 it was 13,762. PEMBROKE, the most westerly county of South Wales, lies to the west of the counties of Cardigan and Carmar then, and is bounded on three sides by the ocean on the S. by the Bristol Channel, on the W. by St George s Channel, and on the N. by Cardigan Bay. Its length from Strumble Head to St Gowan s Head is about 30 miles, and its average breadth a little over 20. The area is 393,682 acres, or about 615 square miles. The coast-line is extremely irregular and extends to over 1 00 miles, the principal inlets being Newport Bay ; Fish- guard Bay, 3 miles in breadth, with an average depth of from 30 to 70 feet, and possessing a good anchorage-ground of mud and sand ; St Bride s Bay, 8 miles long by 8 broad ; and Milford Haven, a splendid landlocked natural harbour, having a length of about 20 miles, and including numerous small bays and creeks. A considerable number of islands adjoin the coast, the largest being Ramsey, which (except ing some small rocks) includes the most westerly land in Wales ; Skomer and Stockham, between St Bride s Bay and Milford Haven ; and Caldy, south of Tenby. The southern coast, consisting of bare, broken, and beetling limestone cliffs, in many cases 200 feet in height, is exposed to the full force of the Atlantic, which in several places has hollowed out long funnel-shaped cavities into which the sea has entrance, the most remarkable being Bosheston Mere, near St Gowan s Head. Owing to the ocean storms the county is almost bare of trees, and the bareness is not relieved or atoned for by mountains, although in many parts of the coast the scenery is wildly picturesque. For the most part the surface is gently undulating, the small rounded hills rising in height towards the north, until they merge in the Preseley range, which runs from east to west and divides the county into two parts, the highest summits being Cwm-Cerwyn, 1754 feet, in the centre of the chain, the lesser eminences of Moel Trigarn and Carn-meyn in the east, and Bwlch-gwnt and Foel Eryr in the west. The principal rivers are the Teifi, which forms for a short distance the north -eastern boundary of the county with Cardiganshire ; the Cleddy or Cleddou, of which there are two branches, an eastern and a western, both flowing south and mingling their waters in Milford Haven ; the Nevern, which flows north into Newport Bay ; and the Gwaen, which flows through a narrow and beautifully- wooded glen to Fishguard Bay. Geoloyy and Minerals. Three -fourths of the county, including the northern portion stretching westwards to the western Cleddou river, and, with certain exceptions, to the Channel, is formed of Llandeilo flags. The Carbonifer ous strata from the South -Wales coal-field extend across the centre of the county from east to west, their area narrowing towards the west. The Pembrokeshire coal-field differs entirely from the South- Wales coal-field both in the lie of the strata and in the character of its beds, due to the occurrence of volcanic action. It is separated also from the main field by an interpolation of Old Red Sand stone. North, east, and north-west it is bounded by beds of mountain limestone and millstone grit, and on the south by Cambrian beds and by the ocean, below which the Coal-measures extend. The strata are composed of Coal-measures, Carboniferous Limestone, and Old Red Sand stone, and are frequently extremely contorted. Igneous stratified rocks also occur in the Preseley range, and in the neighbourhood of St David s Head. The coal is anthracite, and when put on the fire in a wet state emits a blue flame without smoke. About 80,000 tons are now dug annually, the coal being used for furnaces and for smelting and brew ing purposes. There is a lead mine at Llanfyrnach, from which a considerable yield of silver is obtained, the annual value of the ore raised being about <15,000. In caves explored near Tenby and on Caldy Island there have been found remains of various species of extinct mammals. Climate, Soil, and Agriculture. Although Pembroke shire is exposed to frequent violent gales from the south west, the climate in the south is very mild and warm ; and XVIII. 6 1
