122 Progress in Physics. [January, 



was thrust in as before, the burnt air was driven out in the direction shown by 

 the arrows, and the flame continued to burn. On demagnetising the magnet the 

 flame went out, and on immediately magnetising again, the wick, which had 

 become nearly black, began to glow again, and clouds of smoke poured out at 

 each end of the hollow poles in the directions shown by the arrows in the cut. 

 This smoke was of course driven out by the diamagnetism of the heated 

 vapour. On one occasion the heat produced in the wick was sufficient to 

 re-light the taper. 



Some, but not all, of the experiments herein described were shown a few 

 months ago by Mr. Varley and Lord Lindsay, to the Prince of Wales, at a 

 soiree held at the house of Mr. John Pender, 18, Arlington Street, London. 



The Deposition of Iron on the Poles of a Magnet. — At the last meeting of the 

 British Association, a paper was read by Mr. Frederick Varley, F.R.A.S., on 

 " The Deposition of Iron on the Poles of a Magnet," which paper, it will be 

 remembered, attracted considerable attention. He has favoured us with the 

 following details of his plan of coating the magnet ; these details may be of 

 interest, as it is difficult to get a satisfactory deposit, notwithstanding the 

 discoveries of Jacobi in this direction. 



The electro-deposit of iron was thrown down on the poles of a permanent 

 horse-shoe magnet, composed of several bent bar-magnets. Each of the poles 

 was | of an inch square. This magnet was made the electrode of a battery, 

 and the poles were immersed about f of an inch in the solution hereinafter 

 described. A Daniell's battery of one cell with large plates, and having a 

 resistance of 0*33 Ohms was used. The plating solution consisted of equal 

 volumes of saturated solutions of sulphate of iron and sulphate of magnesia 

 mixed together, after which sufficient water was added to make the sp. gr. of 

 the liquid 1400. The plating was effected in a large cell holding about 3 pints 

 of solution, and from the size of the cell the resistance was practically equal in 

 all directions. The cathode consisted of two small pieces of iron, placed at 

 opposite sides of the cell, the magnet being over the centre ; about 1 inch of 

 iron surface was exposed on each side of the cell opposite to the poles of the 

 magnet. The magnet was allowed three months in the solution to receive its 

 electro-deposit of iron, and during that period the mean temperature was 6o°. 



At the end of this time it was found that the iron instead of being uniformly 

 deposited on the surfaces of the poles, as in the case of ordinary electrotyping, 

 was deposited chiefly on the sharp edges of the poles. A bridge of iron was 

 not made from pole to pole as might have been expected, or as would have been 

 the case had iron-filings been scattered over them, but, on the contrary, the 

 growth was equal on all sides of the square poles. The greatest deposit was 

 at the corners of each of the poles. 



This experiment opens the way to a new field of research. For instance, 

 experiments may be made on the deposition of iron inside helices, and the 

 plan shows how magnetic rays may be stereotyped. It also suggests that 

 experiments should be made with thallium, bismuth, and other diamagnetic 

 metals which are easily electrotyped ; the cells in which the work is carried on 

 should be placed between the poles of powerful electro-magnets. Under these 

 conditions, it is reasonable to suppose that the form of the deposit will be 

 modified by the action of the diamagnetism. 



An Improved DanielVs Battery. — The Daniell's battery now commonly used 

 for telegraphic purposes has held its ground so long against all competitors, 

 that at first sight there would seem to be little scope for inventive power 

 applied to its improvement, yet a considerable improvement has just been 

 made by Mr. Octavius Varley, and it is patented by Messrs. O. and F. Varley, 

 of 11, Poultry, London, E.C. 



The following are the defects of the ordinary Daniell's battery: — The sulphate 

 of copper solution diffuses through the porous diaphragm, so that it reaches 

 the zinc plate and covers it with copper ; thus the surface of the zinc which 

 should be positive is made negative, the action of the battery is paralysed, and 

 the zinc plate has to be scraped before the proper electrical action is set up 

 once more. Owing to this defect the full potential of the battery is scarcely 

 ever obtained. Moreover, there is a great waste of the copper salt, for whether 



