RECENT PROGRESS IN PHYSICS. 



ODD 



,he charge of the battery was regularly increased by 1 spark of the 

 leasuring jar, and at each discharge a new needle was magnetized ; 

 |ie strength of the magnetism communicated was then determined by 

 le time which the needle required to make a given number of vibra- 

 lons. A copper wire 2.63 metres long and 1.2966 millimetre diam- 

 j;er was used in the circuit together with the spiral. 

 j In this manner Hankel made a series of experiments whose results 

 [-e represented graphically in fig. 69. The abscissas are '-ronortional 



i the strengths of the battery charges, the ordinates to the strengths 

 { the corresponding magnetization. The ordinates above the hori- 

 jintal correspond to normal, those below to abnormal magnetism. 



This curve does not produce the impression of regularity ; it seems 

 ither to mask some sort of a law by irregularities which cannot be 

 )rrected by computation. But in such cases the law may be repre- 

 ifnted by averages obtained from numerous experiments. 



Hankel says he repeated these experiments with the shortest circuits, 

 ) determine the position of the abnormal, or equally significant weak 

 prmal periods ; from all his experiments with the same kind of needle, 

 ting the same battery of nine jars, he found these periods to occur in 

 ie following charges: 3, 6, 9, 11, 14, 16, 18, 21, 23, 26, 29, 32, 

 p, 40. 



Hankel says, " we see that the change in the polarity returns regu- 

 ■rly ;" but I can find in this series of numbers nothing very clearly 

 ^pressed, and least of all regularity. He says, moreover, that this regu- 



i'rity might have been more clearly represented by the introduction 

 fractions, but he purposely avoided them, as he had not measured 

 em exactly, but only estimated them. 



I Now, what does this mean ? Does not the above series of numbers 

 ^present the means of numerous experiments made under the same 

 iindition ? If this is the case, why hesitate to introduce fractions ? 

 ^ean values are generally computed, not observed. 

 , To render it possible for the reader to judge of the value of his re- 

 filts, Hankel should have told how he arrived at the series 3, 6, 9, 



E, &c. ; and he should have communicated the separate series of 

 periments in order that one might ascertain how far the separate 

 ries differed from the mean on account of accidental disturbances. 



