Nov. 22, 1888] 



NATURE 



95 



A piece of platinum wire about 18 inches long was bent in 

 the middle, and one-half protected by being covered with glass 

 tube and made water-tight at the lower end. After annealing 

 the free portion and testing until perfectly free from all strain 

 effects, it was placed, up to about the middle, in acidulated 

 water, and made the negative pole of a battery, and hydrogen 

 liberated upon it for a few minutes. After being dried it was 

 tested with a small flame at distances i cm. along its whole 

 length. The result was a current from free wire towards that 

 part on which hydrogen had been produced, greatest at the 

 junction of the free wire and the saturated wire. 



When wires of palladium were used, more powerful effects of 

 t]ie same kind were produced." 



Carbon rods were next tried. It was found that when one 



-hese rods was heated and placed against the other, the current 



- always from cold to hot below 200° C. 



They were then used as the electrodes- in decomposing dilute 



sulphuric acid, dried carefully until no current was produced on 



placing them in contact. On heating either rod and joining 



theoQ as before, a current was produced from hydrogen to oxygen 



across the hot junction. 



The same effect was obtained by decomposing hydrochloric 

 1 solution. 



Resistance. — To get rid of possible error from change of tem- 

 I'ciature, two wires of equal length and section were used and 

 balanced against each other. 



These were placed in water, and a current passed from the one 

 to the other, allowed to remain in the acid a little to cool if 

 necessary, and afterwards removed, dried, and placed in an 

 empty glass vessel surrounded with a considerable quantity of 

 water. There they rested until the temperature became the 

 same as the water. When measured, the resistance of the wire 

 containing the hydrogen was found to have increased about one- 

 thousandth part. 



Carbon. —Two thin rods about 2mm. diameter were electro- 

 plated at the ends and soldered to insulated copper wires. 



When used as the poles of a battery the change of resistance 

 wcis considerable, Ijut greater on the rod that had been the posi- 

 tive pole. By using a platinum electrode, hydrogen or oxygen 

 was produced at will upon the same rod, the other rod remaining 

 nnchanged. It then appeared that oxygen increased the resist- 

 ance much more than hydrogen, rising in some cases as high as 

 nine times ; that when oxygen was liberated twice or thrice in 

 succession the resistance increased each time. This continued 

 increase was probably due to chemical changes produced by the 

 active o.xygen. Hydrogen gave an increase of resistance, not 

 continuing beyond a certain point, and not becoming greater on 

 repeated charging with the gas. 



Generally alo the effect of the hydrogen was temporary, dis- 

 appearing, wholly in some cases, partially in others, when short 

 circuited. 



Supirfosition of Polarization.—? 2.xi of the change in the 

 carbon is evidently produced by the mechanical action of the 

 gases evolved, and by the chemical action of the oxygen ; both 

 of these will, however, produce permanent changes. That only 

 part of the action is to be explained in this way is shown by the 

 previous experiments. It is, however, further demonstrated by 

 using two carbon rods in decomposing acidulated water ; after 

 passing the current for one minute, reverse it for one-tenth of a 

 second and immediately join up to a galvanometer. A short but 

 Tiolent deflection appears for the latter contact, gradually falling 

 ♦'^ 'ero and passing to the other side, where it remains for a 

 iderable time, though with much decreased quantity. 

 lie same thing was obtained with platinum electrodes. The 

 occuiid contact, must be very short, or the former polarization 

 disappears. 



7 hermo-eUctric and other Properties of Graphite and Carbon. — 

 In making the previous experiments, I had occasion to place 

 the heated end of one carbon rod in contact with the cold end of 

 another. The temperature of the hot end was varied from 30° C. 

 to a red heat, whilst the cold end was kept at about l^''Q. 



Currents of electricity were of course produced. When the 

 temperature of the hotter rod was raised but slightly, the current 

 was fn m cold to hot through the point of contact, but when it 

 was raised to a red heat the current passed from hot to cold. 



I was led to expect that the line of carbon in a thermo-electric 

 diagram, in which the area of the space between the lines is pro- 

 portional to the electromotive force, would show a bend of some 

 kind, and as no researches were known showing such a bend, 

 it appeared desirable to test it carefully. 

 Near one end of a carbon rod a hole, about 5 mm. in diameter. 



was drilled, and into this the end of a platinum wire was inserted 

 and fixed by being wedged with a piece of rod carbon. The- 

 whole was thoroughly covered with Indian ink, which, where 

 dry, was again covered with clay. The carbon rod was insulated 

 from the platinum wires, and they from each other by thin sheet 

 asbestos and mica, by which means it was insulated from the 

 vessel in which it was placed, and luted with clay to prevent 

 access of air. From several series of experiments a thermi- 

 electric line was calculated, and found to rise from 0° to 250",. 

 beyond which it descended at the same rate. 



OU.er Changes in the Properties of the Body at the same 

 Temperature. 

 This change in the ihermo electric power of carbon is accom- 

 panied by other changes. The resistance, the expansion, and 

 t le spcLiHc hsat all appear to undergo a corresponding alteration,, 

 as the following summary of results shows : — 



Abave 250° C. 

 Current fron> 

 hot to cold. 



A. Effect of contact of 



hot and cold car- 

 bon. 



B. Theimo-electric line 



C. Rate of decrease of 



resistance per de- 

 gree per ohm 



D. The rate of increase 



of the coefficient 

 of expansion 



E. Rate of increase of 



the specific heat 



Below 250" C. 



Current from 



cold to hot. 



Rises. 

 Diminishes. 



Increases. 



Fairly regular. 



Falls. 

 Increases. 



Decreases. 



Falls to half. 



Geological Society.— November 7.— Dr. W. T. Blanford,. 

 F.R.S., President, in the chair. — The following communica- 

 tions were read : — The Feimian rocks of the Leicestershire 

 coal-field, by Horace T. Brown. According to Mr. Brown,, 

 the Permian rocks, of the Leicestershire coal-field belong to the 

 same area of deposition as those of Warwickshire and South 

 Staffordshire, all having formed part of the detrilal deposits of 

 the Permian lake which extended northwards from Warwick- 

 shire and Worcestershire, and which had the Pennine chain on its 

 eastern margin. Lie pointed out the dissimilar nature of these 

 deposits to those of the eastern side of the Pennine chain from 

 Nottingham to the coast of Durham. There were proofs of the 

 existence of aland barrier, owing to the uprising of the Carbonifer- 

 ous,between the district round Nottingham and the Leicestershire 

 coal-field. The mcst northerly exposure of the Leicestershire 

 Permians is thirteen miles south-west of those of South Notts. 

 He indicated the probable course of the old coast-line of the 

 western Permian lake. Denudation had bared some of the 

 older Palaeozoics of their overlying Coal-measures, and it is the 

 rearranged talus from the harder portions of these older rocks 

 which now forms the brecciated bands in the Leicestershire Per- 

 mians. The reading of the paper was followed by a discussion, 

 in which the President, Prof. Bonney, Mr. Whitaker, Prof. 

 Blake, and Mr. Topley took part. — On the superficial geology 

 of the central plateau of North- Western Canada, by J. B. 

 Tyrrell, L'ield Geologist of the Geological and Natural History 

 Survey of Canada. The drift-covered prairie extends from 

 the west side of the Lake of the Woods to the regiort 

 at the foot of the Rocky Mountains, rising from a height 

 of 800 feet on the east to 4500 feet on the west, the gentle 

 slope being broken by two sharp inclines known as the Pem- 

 bina Escarpment and the Missouri Coteau, giving rise to the 

 First, Second, and Third Praire Steppes. The author described 

 the older rocks of this region, referring especially to his sub- 

 division of the Laramie formation into an Edmonton series of 

 Cretaceous age, and a Pascapoo series forming the base of the 

 Eocene, and then discussed the superficial deposits in the 

 following order: (i) Prcglacial gravels ; occurring along the 

 foot of the Rocky Mountains, composed of w aterworn quartzite 

 pebbles, similar to those now foiming, and, hke them, pro- 

 duced by streams flowing from the mountains ; (2) Boulder- 

 clay or 'Jill ; (3) Interglacial deposits of stratified material ; 

 (4) Moraines; (5) The Karnes or Asar, generally occurring 

 at the bottoms of wide valleys ; (6) Stratified deposits and 

 beach-ridges which have been formed at the bottoms and along 

 the margins of fresh-water lakes lying along the foot of the 

 ice-sheet ; (7) Old Drainage-channels. Some remarks on this 

 paper were made by the President, Dr. Ilinde, Mr. Whitaker^ . 

 Mr. Topley, and Mr. Marr. 



