NATURAL PHILOSOPHY. 157 



great differences of temperature, so as to avoid the necessity of 

 using ice ; that they should not be exi3ensive ; and that the insu- 

 lating material ^oukl resist a high temperature, and possess suf- 

 ficient solidity .uid elasticity. The thermo-electric battery in 

 question was constructed in reference to the use of a gas llame. 

 The single element consists of bars of unequal dimensions, the 

 positive bar being 7" long, 1'" broad, and h'" thick ; the negative, 

 6" long, 1'" broad, and &" thick. Marcus puts together 32 

 elements in such a manner that all the positive bars are on one 

 side, and all the negative bars on the other, and have thus the 

 form of a grating. The battery consists of two such gratings, 

 which are screwed together in tlie form of a roof, and strength- 

 ened together by an iron bar, mica being used as an insulator. 

 The under sides of the elements are cooled by a vessel of water. 

 The whole battery has a length of two feet, with a breadth of six 

 inches, and a height of six inches. Marcus has constructed a fur- 

 nace, which is calculated for a battery of 768 elements, which 

 would correspond to a Bunsen's battery of 30 pairs, and consume 

 240 lbs. of coal per day. The Vienna Academy, recognizing the 

 imijortance of the discovery, has voted to the inventor the sum of 

 2,500 guilders, the invention to be public projierty. Pogg. Ann., 

 April, 1865; from " Amer. Journ. of Science" for, Sept. 1865, 

 the Editor of which appends the following note : — 



" The importance of Marcus's invention, in a technical point of 

 view, can hardly be over-estimated, since it promises to fui-nish 

 the cheapest method of obtaining an intense light for light-houses 

 and public buildings ; and even holds out a prospect, perhaps not 

 remote, of applications in domestic economy. 



"It must be remembered that the step taken by Marcus is, after 

 all, a first step in the right direction. Bunsen, E-. Becquerel, and 

 Stefan, have shown that there are thermo-electric combinations 

 of much higher electro-motive force than those employed by 

 Marcus, although the internal resistance is too great to permit of 

 their use in constructing large batteries. If the i^rogi'ess of 

 science should make us acquainted with metallic alloys, which, 

 when combined and arranged as thermo-electric elements, de- 

 velojj electro-motive force as high as one-tenth of that of a Bun- 

 sen cell, the thermo-electric battery will again become a new 

 instrument. Iji this connection, we suggest that the thermo- 

 electric relations of the highly crystalline alloy of iron, manganese 

 and carbon, known as ' spiegeleisen ' (that from the Franklinite 

 of New Jersey for examjile), deserve a careful studJ^ The i^os- 

 session of a galvanic battery in which coal is consumed in i^lace 

 of zinc and acids, can hardly fail to revive an interest in electro- 

 magnetic engines, like that of Page, even if only for cases in 

 which comparatively little jjower is required, since bur best steam 

 engines do not yield ten per cent, of the work which the con- 

 sumption of the coal is capable of doing." 

 14 



