412 



effect 38 times greater than can be obtained by the consumption of 

 the same fuel in the ordinary mode of chimney ventilation. Accord- 

 ingly, he strongly advises the adoption of the former in preference 

 to the latter: and inveighs against the stove-doctors of the present 

 day, who, on pretence of economy and convenience, recommend 

 the slow combustion of a large body of coke, by means of a slow 

 circulation of air ; under which circumstances, it is well known to 

 chemists that much carbonic oxide, a gas highly pernicious to all 

 who respire it, is generated; accompanied, at the same time, by a 

 comparatively small evolution of heat. In order to obtain the 

 maximum quantity of heat from a given mass of fuel, its combus- 

 tion, he observes, should be very vivid, and the evolved caloric 

 should be diffused over the largest possible surface of conducting 

 materials; a principle which has been judiciously applied in several 

 French factories. It has been proved that work-people employed 

 in calico-drying rooms, heated according to the plan here repro- 

 bated, become wan, emaciated, and diseased ; while in rooms in 

 which the air is more highly heated by means of steam-pipes, they 

 preserve their health and florid complexion. 



16. " An Experimental Inquiry into the Relative Merits of Mag- 

 netic Electrical Machines and Voltaic Batteries, as Implements of 

 Philosophical Research." By William Sturgeon, Esq., Lecturer 

 on Natural and Experimental Philosophy at the Honourable East 

 India Company's Military Academy at Addiscombe. Communicated 

 by P. M. Roget, M.D., Sec. R.S. 



The first part of this paper is occupied by a description of two 

 forms of constructing the magnetic electrical machine, which the 

 author has adopted ; and the second, with the particulars of some 

 experiments made with a view to determine the respective powers 

 of these machines as compared with the common voltaic battery. 

 In the first form of the instrument, a reel, round the periphery of 

 which 200 feet of copper wire, one 20th of an inch in diameter and 

 covered with stout sewing-silk, are coiled, is made to revolve on a 

 spindle, placed in the axis of a system of horse-shoe magnets, so as 

 to remain within the branches of the latter during its whole revolu- 

 tion. The electric currents produced in the copper wire by mag- 

 netic induction, while the coil is moved at right angles to the plane 

 of the magnets, are conducted by means of four semicircular me- 

 tallic flanges attached to the spindle, into cisterns of mercury, the 

 one being positive, and the other negative ; and which consequently 

 act as the two poles of the battery. In the second form of the ap- 

 paratus, a piece of soft iron, of which the ends are bent into the 

 shape of two arms, and which is surrounded with a coil of 300 feet 

 of copper wire, is made to revolve in front of the poles of a horse- 

 shoe magnet $ its axis of motion coinciding with that of the magnet; 

 and the electrical currents determined in the wire by this rotation, 

 being collected in the same manner as in the former instrument. 



The author next details several series of experiments which he 

 made for the purpose of ascertaining the relation observable be- 



