PEIRCE. — DEMAGNITIZING FACTORS OF CYLINDRICAL RODS. 61 



We thought it possible that we might avoid this difficulty by using 

 at the same time a long piece and a short piece, cut freshly from a 

 single rod, but experiment seemed to show that we could not expect 

 the same permeability in two pieces obtained in this way and that the 

 difference might easily be as much as one per cent at some excitations. 

 We believe, however, that we have reduced the error in our conclusions 

 due to the effect just mentioned to a very small fraction. 



All our work, which lasted more than two months, pointed to the 

 same results, and I need mention only a few representative experi- 

 ments. They convinced us that in our determinations of the satura- 

 tion values of the magnetization in different kinds of iron and steel, 

 we might safely use much shorter test pieces than those which we had 

 employed before. 



Experiment A was made upon an annealed piece of Bessemer rod 

 0.635 cms. in diameter. The original length was 158 diameters, but 

 this was cut down successively to 61, 31, and 18 diameters. At an 

 excitation of 2600 gausses where B was 23530, the average of the 

 fluxes of magnetic induction through the central sections of the 

 various pieces, differed by less than one sixth of one per cent from 

 an3 r one of the individual values, and from the last value by a wholly 

 inappreciable fraction. 



Experiment B was made upon a Bessemer rod 0.795 cms. in diameter. 

 The lengths of the pieces were 150, 100, 60, 40, and 20 cms. For 

 H 1320, the flux through the central section of the shortest piece 

 seemed to be about one fifth of one per cent lower than the average 

 of the corresponding fluxes for the other pieces. At 1850 gausses and 

 2700 gausses, however, there was no such difference. For H 2570, 

 B was 23700. Figure 3 shows some B-H curves for the pieces at low 

 excitations where the effects of the presence of the ends of the rods 

 are very apparent. 



In Experiment C, we treated a somewhat stouter Bessemer rod. 

 Its diameter was 0.879 cms. Its length was originally 164 diameters, 

 but this was shortened by steps to 124, 100, 75, 45, and 24 diameters. 

 At 2500 gausses the value of the flux through the centre of a piece 

 only 19 cms., or 24 diameters, long,ldid not differ by so much as one 

 tenth of one per cent from the mean of the fluxes for all the lengths 

 under this excitation, where B was 23550. At an excitation of 1710 

 gausses, B was 22700, and it was not possible to prove that the shortest 

 piece had a less flux than the others. Some of the results of our 

 observations for this experiment are tabulated in Table V. H is the 

 value that the field would have inside the solenoid if the iron were 



