1865.] Physics. 325 



ignited by the electric spark. Contact is made and broken by the 

 rotary action of the crank shaft, and the explosive force, consequent 

 on the ignition, gives motion to the piston on each side alternately. 

 The cylinder has a water jacket surrounding it, through which a 

 stream of cold water is kept gradually flowing, to absorb any excess 

 of heat. The mixture exploded is about eleven volumes of air to one 

 of gas. The consumption of gas is as near as may be seventy feet 

 per horse-power per hour of actual work, giving a cost, with gas at 

 4s. 6d. per thousand feet, of about 4d. Besides this cheapness, the 

 engine is recommended by its simplicity, cleanliness, and safety. 

 When set in motion, the machine requires no attention, and the 

 batteries only want charging once a week. 



Electeicitt. — A very ingenious battery, which is said to be both 

 constant and cheap, has been proposed by Mr. Arthur Eeynolds, B.Sc. 

 The exciting liquid being a solution of perchloride of iron, and the 

 metal to be attached metallic iron, the copper plate being replaced 

 by carbon. The action of the battery, according to the inventor, 

 would be quite constant, as the exciting liquid would always remain 

 in the same condition. The iron dissolving by reducing the solution 

 to protochloride, which being oxydized by the air, would be deposited 

 so that the solution would always remain of the same strength. This 

 would be as cheap, or cheaper, than any other form of battery, and 

 perpetually constant. The purpose to which it is proposed to employ 

 the battery, is to the . manufacture of magnesium from sea-water. 

 The sea-water should be evaporated with a little chloride of calcium, 

 and after the main bulk of common salt and sulphate of lime had 

 crystallized out, the solution should be evaporated to dryness. The 

 dry mass melted and decomposed by the above-described battery. 



Professor Bunsen has desci'ibed some powerful thermo-electric 

 piles, which are likely to prove of great value. Hitherto, bismuth 

 has occupied the highest, and an alloy of two parts of antimony, with 

 one part tin, the lowest place in the thermo-electric series. It has 

 now been shown that pyrolusite stands above bismuth in the series, 

 and that copper pyrites occupies a far higher place than even pyrolu- 

 site. When copper pyrites is combined with the above alloy, so as to 

 form a thermo-electric pair, or, better still — in order to be able to 

 employ greater differences of temperature — when copper pyrites is 

 combined with copper, far stronger currents are obtained than, under 

 the same circumstances, are yielded by any of the themio-electric 

 piles hitherto in general use. When heated to above the temperature 

 of melted/ tin, the other end being cooled in water of 60° C, one 

 single element exhibited a ten times greater action than a bismuth 

 and antimony element of equally effective resistance when heated 

 from 0° to 100° C. Ten of the above described pairs formed into a 

 battery suffice to give all the actions of a Daniel's element, containing 

 an effective copper surface fourteen square centimetres in area. 

 Copper pyrites, in its natural state, melts easily at a strongly glowing 

 heat without sensible decomposition, and it may then be cast into any 

 mould whatever. It is a remarkable fact, however, that this sub- 



