356 



RECENT PROGRESS IN PHYSICS. 



2. The seiles of experiments represented by fig. 69, were compared 

 Avitli two others in which the spirahs were so moved in the directio n o 

 their length that the needle covered only 28 coils in the second, andf 

 only IH in the third series. The general result was, that the periods I 

 were longer in proportion as the needles covered fewer coils. 



3. As mentioned above, Kiess announced the proposition that, in dis- ' 

 charging a ])attery, no part of the circuit acts inductively upon itself. 

 Hankel contests this proposition. He comes to the opposite conclu- 

 sion from the following experiments : 



A cop])er spiral of tolerably large diameter was surrounded by a 

 similar spiral, the two being so arranged that the discharge could at 

 pleasure be made to pass through the two, either in the same or in 

 opposite directions.* A magnetizing spiral was also introduced into the i 

 circuit The march of the magnetizing periods for both arrangements I 

 being then compared they did not harmonize, and hence Hankel i 

 inferied that there was necessarily an interference of effects. 



Even if it be conceded that Keiss' experiments are not sufficient td : 

 establish hie proposition, those of Hankel are still less fitted to over- 1 

 throw it ; for, in the phenomena of magnetism by the discharge stroke, ; 

 our knowledge of what is regular or what may be accidental is not : 



such as to permit a safe conclusion to be drawn from the want of coin- 

 cidence of two such series of experiments. 



The differences which occur in magnetizing steel needles, accordiug 



* Hankel gives the lliickness of tlie wire 'o the xTJT^iT^'o ''^ ^ millimetre, which appears to 

 mc an unnecessary accuracy, considering the other relations of this series of experiments. 



