218 Mr. J. R. Ashworth. Methods of making Magnets 



And it may be calculated that if No. 34 had just been dissolved so 

 far as to have a dimension ratio of about 110 to 115, it would have 

 exhibited a zero coefficient. Since the former series of wires with 

 dimension ratios of this magnitude would have had large negative 

 coefficients, there must be some important physical or chemical 

 differences between these and the former wires influencing the 

 character of the coefficient. 



To complete the series of experiments on the influence of the di- 

 mension ratio it was desirable to perform the converse operation and 

 to prove that an originally negative coefficient would become positive 

 by increase of thickness. 



Three pieces, (a), (&), (c), of No. 33 wire were cut from the same 

 coil, each 12 cm. long, magnetised and then heated and cooled sepa- 

 rately in the same way. The coefficient was about — 0*000119 for each. 

 (a) and (6) were then bound together with fine copper wire, like poles 

 being in contiguity ; the coefficient as now determined was almost 

 zero. The piece (c) was then joined in the same manner to its two 

 fellows and the coefficient again determined ; it was now 4- 0*000105. 

 The experiment is conclusive, for it is allowable to regard bundles 

 of wires as rods of equivalent cross section.* 



Wires drawn to different thicknesses are not structurally suffi- 

 ciently identical to allow of strictly comparable magnetic results. 

 It is therefore more satisfactory to vary the dimension ratio by 

 altering the length and keeping the diameter constant. A series of 

 tests were conducted in this way. Lengths of 3, 6, 9, 12, 15, and 

 18 cm. of No. 30 wire were cut from the same coil, separately 

 magnetised, and the coefficient of each very carefully determined. 

 Table VI gives a complete view of the results. 



Table YI. 

















No. 



21. 



R. 



it. 



/• 





a. 



o-oo. 



30 



3 cm. 



15 95 



137 '4 



78 -7 



0-427 



+ 0261 



J5 



6 „ 



31-90 



313 -4 



204-0 



0-349 



+ 0151 



}> 



9 „ 



47*85 



483-2 



378-3 



0-217 



-0084 





12 „ 



63 -80 



602-0 



513-8 



0-147 



-0225 



>> 



15 „ 



79-75 



683 -1 



595 -0 



0-129 



-0296 





18 „ 



95 -70 



726-8 



637 -4 



0-123 



-0317 



Diameter of each piece, 0'187 cm. 



* Yon Waltenhofen, ' Wien. Ber.,' vol. 48, part 2, p. 578, 1863. Ascoli and 

 Lori, ' K. Accad. dei Lincei,' Eome (5), 3, 2 Sem., p. 157, 1894. 



