186 Review of M. Aitn4 on a New Method of Making Magnets. 



this difficulty that the paper, the substance of which we are about to pre- 

 sent to our readers, has been directed. 



M. A\m6 proposes to bestow temper and raagnetisra at once upon a bar 

 of steel, in the following manner. 



Let a horse-shoe shaped bar, of soft iron, be encircled with a brass wire, 

 covered with silk ; let the two extremities of this wire be connected with 

 the poles of a voltaic battery ; take a straight bar of steel, long enough to 

 connect the two limbs of the horse-siioe, and heat it to a red heat; then 

 with a pair of pincers, apply the ends of the bar to those of the horse-shoe, 

 and plunge the whole into cold water. After an immersion of a minute or 

 two, remove the first bar, and repeat the process with others, drawn suc- 

 cessively from the fire. 



Lest the wire should be injured, the two extremities of the coil, when 

 tl.e apparatus is dipped into the water, should be enveloped in linen 

 covered with mastich. The ends of the conducting wire should also be 

 soldered to the zinc and copper poles of the battery. A single wire has 

 been employed ; it would perliaps be preferable to unite many such into a 

 bundle, or to use a strip of copper, covered over with silk or varnish. 



The bar should not be detached too rapidly from the horse-shoe ; it is 

 necessary to wait until the interior of the steel is of a very reduced tem- 

 perature, so that its molecules may be disposed properly for magnetism 

 and temper. 



The time of the immersion should always be short, though varying with 

 the bulk of the bar, and the temperature at which it is applied. We have 

 thus an easy method of procuring any number of magnetised steel bars. 

 By this method may also conveniently be prepared magnets, " en faisceau," 

 and perhaps compass needles, since it affords a facility for magnetising 

 almost as powerfully bars of a hard, as those of a softer temper. 



The above process may be applied also to masses of the magnetic oxide 

 of iron ; only, it is perhaps more advantageous not to temper them. 



The two effects are upon trial. In neither case is it very probable that 

 the condition of the oxidation of the surface is in any great degree modi- 

 fied by the elevated temperature, especially when precautions, which it is 

 easy to imagine, are taken against the presence of the oxygen of the 

 atmosphere. 



^ Treatise on the principal Mathematical Instruments used in Surveying, 

 Levelling, Astronomy, S^c. By F. TV. Simins. London, Troughton and 

 Simms, 1834. pp. 108. 



This is a short tract, wherein the principal mathematical instruments 

 in use among surveyors and astronomers are enumerated, described, and 

 figured, and the method of employing them concisely explained. The 



J 



