T Ii 



'I 1 



Some of the moat .simple experiments by which the 

 l thermo-flcctricitv niav be illustrated are those 

 lich, soon ir 



ill of Utrecht. i.K/i/i/'- .r//,i/,No. 



A slip of copper bent in the form of a semicircle 

 was attached (in close contact), at its extremities, to t he- 

 end* of a bar of antimony about fifteen inches long ; and 

 uiid in the direction of the magnetic mcri- 

 wire above it, a small compass needle \\.-\~ 

 :, or supported on a pivot between them. On 



mity of t: 



a lamp, the north end of the" needle wa- I to de- 



towards the wot. Again, when a slip of rinc and 

 if copper v. io that, nil the i being 



apph- L* formed a parallelofrnon having 



.auctions of the slips in the middle of the shorter 

 sides, and a compass needle ;ded within the 



circuit, on placing the apparatus in a plane coinciding 

 with the magnetic. meridian, with the longer sides parallel 

 to tli- ,'cr slip being uppermost) and 



heating the northern point of junction, the needle deviated 

 toward* the west : the apparatus being inverted so that 

 the zinc slip was uppermost, cm heating the northern junc- 

 tion as before, the needle deviated towards the east. It 

 follows from these experiments that the fluid current, if 

 such it be, which affects the magnetism of the needle, cir- 

 culates about the copper slip in such a manner that when 

 the latter is in a horizontal position its direction is from 

 west to east, passing above the slip, in a plane perpendi- 

 cular to its length: this effect is similar to that which 

 takes place, though in a contrary direction, when a mag- 

 neti/.ed needle is brought near a conducting wire joining 

 the poles of an ordinary galvanic apparatus; for if the 

 conducting wire be placed in a horizontal position in the 

 lion of the magnetic meridian, with the copper, or 

 the negative end of the apparatus towards the north, and 

 the needle be below the wire, the north end of the needle 

 deviates towards the east ; it' above the wire, towards the 

 west. 



Effects similar to those which result from the applica- 

 tion of heat take place when one extremity of the bar of 

 antimony, or one of the junctions of the zinc and copper, 

 is made colder than the other by means of ice. 



When both ends of the bar were heated, no deviation 

 was produced in the needle ; and after deviation had taken 

 place by heating one end only of the bar, in proportion 

 as the h'eat tended to a uniform diffusion, the needle 

 dually returned to the direction of the magnetic meridian. 

 Thermo-electric circuits mav be formed in a ring con- 

 _' of two curved bare of different metals, as bismuth 

 and copper, each being in the form of a semicircle, and 

 the two being attach ler in the direction of a dia- 



meter; or they may be produced in a rectangle made by 

 gacing in close contact four bars of metal, of two dif- 

 rent kinds, following one another alternately. M. 

 Oersted formed a hexagonal circuit with si\ pieces, three 

 of bismuth and three of antimony, which were disposed 

 in alternate order: on heating, by means of a Ipirit-Iamp, 

 one of the places of junction in the rimr, or in th. 

 angle of four pieces, a compass-needle placed within or 

 below the plane of circuit was found to deviate ; and it 

 deviated still more when the opposite angles of the rect- 

 angle .led. In the. experiment with the hex- 

 agonal circuit the uter in proportion to 

 the number of alternate joints which were heated. .Simi- 

 lar effects were produced when the alternate joints were 

 artificially cooled; but the deviation was the !_'. 

 when the alternate joints were heated and the others were 

 cooled. 



By doubling the lengths of the bars in a rectangle com- 

 posed of four, the di than that which was 

 produced by the smaller rectangle ; but when the larger 

 rectangle was composed of eight pieces, the deviation 

 wa* greater. 



mntry the subject of thermo-electricity has been 

 diligently pursued by Professor Gumming of Cambridge. 

 who appear* to have entered upon it without any other 

 knowledge of the discovery of Scebeck than the simple 

 fact that electro-magnetical action was produced by heat- 



ne end of a bar of antimony, to the ext 

 which were made fast those of a brass wire; and tin 

 detail* of his researches are contained in a memoir which 

 u published in the Cambridge Philosophical Tran*ac 



for 1823. From ;ipears that all jtfrfeot conduc- 



tors of I'lectricitv r cooled i 



action, which is indicated bv the amount 



in all .substances, and with some the direction of the cur- 

 rent is contrary to that which is produced 

 \Vheii a single bar, of symmetn 

 middle, it produce* no ell- 

 cause the opposing currents counteract IM 

 in a ring formed of two metals, who. i the 



points of junction, the fluid seems to pass from one : 

 to the other; so that one loses positive el. r be- 



comes negative, win! irnes positi 



Professor Cummini; haviiur asccrtai; \periments 



on bars of bismuth, which were mail. v hot and 



cold, and v I in contact with each other 



pair of the hot and cold p.-i - the two , 



of the whole compound bar, bcin-r connected together by 

 . that the action of the whole bar on a needle vr* 

 i- than that of any two portions, o: 1 the 



other cold, was led to the'ii: 

 may be exhibited by the mere ju\t;: 

 finite number of small plate-. He 

 determine the thermo-electric relations of different : 

 by merely placin<: i: \\ith each other a small 



portion of each of the two kinds of metal to be examined, 

 and touching first one of them, and then the other, with 



nd of a silver or copper wire which was com; 

 with the heated bar. When the metals were bismur 

 antimony, the former, on being touched, caused the 



ii-edle to deviate so as to indicate positive electricity, 

 and the latter so as to indicate negative . 

 in the memoir above quoted there is given a us 

 of the electrical relations of metals in several dill 

 combinations. In the same memoir there is also an ac- 

 count of several curious anomalies which were observed 

 in the magnetic action: one of thc.-e is. that when iron 

 wire is used to touch the metals examined, of which one 

 is iron, the needle deviates a certain number of 

 the positive direction ; then, as the heat of t 

 increased, the deviation in that direction gradually dimi- 

 nishes till it becomes zero ; after which the deviation ' 

 place in a negative direction, and it becomes a maximum 

 in this direction when the wire acquires a red h 



If two parallel bars of bismuth are connected at 

 extremity of each by a bar of antimony, so as to form 



ide- uf ;i square, and the opposite cv 

 bars of bismuth are connected with the two extremis 

 the bent wire forming an electro-magnetic multiplier 

 [KI.KITRO-MAGN-ETISM, p. 342, vol. ii.], the. needle of the 

 multiplier deviates very little; but when those ends of the 

 o connected by means of a fourth bar. the effect on 

 the needle is considerable. Now the effect of the gal- 

 vanic or hydro-electrical current, when produced by 

 and zinc, with common water as a conductor, is vcrv small ; 

 and hence it U inferred that the thermo-electrical current 

 L.'i\c> rise to a large quantity of that whiei ise of 



the macnc: 1 the power being however in a low 



state ol 



THEKMO'MKTKK from the Greek words Oi.ojioc, hnt. 

 and n'lrpov. is an iiistiumeiit by which the tcm- 



:cd. It consists of a 



tube with a capillan linim; in general aK 



or mercury, which expanding or contracting by 

 in the temperature of the atmosphere, or on the instru- 

 ment bi-intr immersed in the liquid or gas which is to be 

 examined, the st phere, liquid, or gas, with 



! to caloric- is indicated by a scale which is either 

 applied to the tube or engraven on its exterior MI; 



The end proposed by a thermometer istli. ment 



temperature of any body with relation to the tem- 

 perature of Mime other substance, as . the point 

 of free/ing: but the measure so obtained must not be 

 understood to express the absolute miantity or density of 

 caloric in anybody, it being well 1. 

 substances, though exhibiting the same apparent tempera- 

 ture, contain very dill. of caloric according 

 to their cttjtacitirs for that, element. 



The thermometer must have been in use in the begin- 

 ning of the seventeenth century, but it is not known, 

 precisely, to whom the honour of the invention is due. A 

 physician of Padua named Sautorio, and Cornelius Dreb- 



