366 Scientific Proceedings, Royal Dublin Society. 



the same as I found for the fine wire in the soft state. Mr. 

 Ivatt tried to harden it, and writes : — " Heating the No. 13 wire 

 to redness, and allowing it to cool very slowly, is, I find, the only 

 way to harden it." This rendered the wire hard and brittle, and 

 apparently lessened its tenacity, for the same wire now broke at a 

 stress of 38*3 tons per square inch. 



It will be interesting to compare the tenacity of the manganese 

 steel wire, in grammes per square centimetre, with that of iron and 

 steel. According to Sir W. Thomson (Art. " Elasticity" Encyc. 

 Brit., new edit.), the tenacity or breaking stress of — 



Iron wire is, . . 625 to 651 x 10 4 grammes per sq. cm. 



Steel wire, . . . 859 to 991 x 10* „ ,, 



Best pianoforte steel wire, . 2362 x 10* ,, ,, 



Common pianoforte steel ) ., c , , n , 



r } 1851 x 10* ,, ,, 



wire, I " 



Hard manganese steel wire, 1735 x 10 4 ,, ,, 



The two last are my own determinations. 



Electric Resistance. — I next determined the electric conductivity 

 of the wire. For this I employed No. 19 wire, 0*96 mm. dia., in 

 a length of 510 cm. This had a resistance of 5'22 ohms, i.e. 

 practically an ohm per metre. The resistance of the hard and soft 

 wire were exactly alike. The specific resistance was 0"000077 of 

 an ohm, or 77,000 O. Gr. S. units for a cubic centimetre. This is 

 very high : the sp. resistance of ordinary iron is 9827 C. Gr. S., and 

 of German silver wire 21,170 O. Gr. S. units per centimetre cube. 

 Experiments are in progress to determine how far its resistance is 

 affected by change of temperature ; but, in any case, the remark- 

 ably high resistance of manganese steel wire points to a useful 

 application of this material for the construction of resistance coils 

 for electric lighting and other purposes. 



I now come to the next and most interesting feature of this 

 steel — its magnetic inertness. 



Magnetic Co-efficients. — Mr. Bottomley, in his note before the 

 British Association, to which I have referred, stated that he had 

 submitted the bar of manganese steel to an enormous magnetising 

 force (far beyond what would be necessary to saturate ordinary 

 steel), and after the magnetisation of the manganese steel he had 

 determined its intensity of magnetisation, by the deflection of a 



