on the Magnet!*- Prop, ,■(!< s of Steel and Iron. 181 



Kohlrausch, to study the matter somewhat more systematically 

 than hitherto has been done, with especial reference to the 

 question, whether there are any qualitative differences between 

 the effects of the two kinds of hardening on the magnetic prop- 

 erties of steel and iron. 



2. Division of the work. — The work divides itself naturally 

 into a consideration of the effect of the mechanical hardening : 

 1st, on the permanent magnetism of saturated magnets ; 2d, 

 on the temporary, as well as the permanent magnetism, by va- 

 rious intensities of the magnetizing force. 



3. Material. — In regard to the material used it should be sta- 

 ted, that experiments were made with steel and iron from many 

 sources. The kind of steel chiefly employed however, was that 

 known as "English Silver Steel'," which was obtained from 

 Crooks Bros, in Sheffield and Manchester, in the form of wires, 

 330 mm long, with the diameters l-0 mm , l-2 mm and l'6 mm . The 

 iron magnets were cut chiefly from a long piece of soft " Com- 

 mercial Iron Wire," having a diameter of l-6 mm . 



All the material, when the contrary is not stated, was sof- 

 tened, before being used for the experiments, by heating it in 

 an iron box filled in with forge scales. After the box with its 

 contents had been at a red heat for some time the fire was al- 

 lowed to die out, the material remaining in the forge until it 

 had cooled down to the ordinary temperature. After the wires 

 had been softened every precaution was taken to prevent any 

 unintentioned hardening. 



4. Hardening. — The wires were hardened either by " bend- 

 ing." •'stretching," "hammering," or "pulling" them through 

 holes in the well-known apparatus for reducing the diameter of 



bling us to obtain ■ 

 very nearly equal diarne 

 hardness are to be obtained they may be pulled, for example, 

 « (b) through [1] and 

 [2], and wire (c) through hole [1] ; they are then softened and 

 wire (c) pulled through [2] and [3], wire (b) through 8 and 

 wire On left soft, nil thus having the diameter of hole [3]. 

 This advantage, however, is more than counterbalanced by 

 the fact, which was evident in many ways, that the hardening 



i very irregu 

 By far the 



vere made with 

 apparatus [Per- 



reaux] for determining the " breaking weight," the weight being 



read off by an index in kilograms. 



