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XXXVII. Intelligence and Miscellaneous Articles, 



ON THE CHANGES WHICH STRETCHING AND THE PASSAGE OF A 

 VOLTAIC CURRENT PRODUCE IN A MAGNETIC BAR. BY M. 

 VILLARI OF NAPLES. 



MATTEUCCI states that if a bar of hard iron which is magnetized 

 by a spiral is stretched, the magnetism of the bar increases. If 

 the stretching ceases, the magnetism again diminishes. If the same 

 experiment is made with soft iron, the reverse is the case. If the mag- 

 netizing spiral is not at work, stretching also causes an increase of 

 magnetism, and relaxation (nachlasseri) a diminution. 



Wertheim has repeated Matteucci's experiments, but only con- 

 firms his results in case the magnetizing spiral is at work. He adds 

 at the same time that the deflection of the galvanometer observed 

 is smaller each time the stretching is repeated and the more the 

 wire is straightened. He doubts, therefore, whether with a per- 

 fectly straight wire, stretching alters the magnetism of the wire. 



As no further statements exist respecting stretching, it appeared 

 desirable to make a few new experiments on the subject, in order to 

 explain the difference between Matteucci's and Wertheim's experi- 

 ments. The apparatus consisted, like Matteucci's, of two spirals, 

 a magnetizing and an inducing one, in the latter of which a Wie- 

 demann's mirror galvanometer, with sliding coils, was inserted. 



In this method it is not the existing magnetism of the iron or steel 

 bar which is measured, but the inducing-action which a change in it 

 produces. But the subesquent investigation only refers to changes ; 

 and these may very well be measured by the induction which they 

 produce. 



The apparatus employed was the following : — 



One spiral was firmly fixed in the other, and they were well fas- 

 tened in a frame which stood on a table, and in such a manner that 

 their common axis was from east to west. The galvanometer was 

 at a distance of 4 to 5 metres from the spirals. The bar of steel or 

 of iron which was to be used for experiment, was inside the inner 

 spiral. At each end of the bar a thick brass wire was soldered, or 

 else screwed. In order that neither these wires nor the bar to which 

 they were fixed should move laterally, they passed through two 

 pieces of wood which were firmly united with the frame in which 

 were the spirals ; and they also passed through corks which stuck 

 in the ends of the inner spiral. One end was fastened to the stand 

 by means of a screw, at the other was a rope which passed over 

 a pulley, and by means of a lever could be stretched by 240 

 pounds. 



The steel and iron bars, before being placed in the apparatus, were 

 moreover straightened as much as possible, and after they were in- 

 serted were repeatedly drawn and, in order that they might be 

 straight, were stretched by 40 pounds. 



