638 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Most of the specimens mentioned in the experiments discussed below 

 were packed, one or two at a time, in fine iron filings, enclosed in a 

 piece of large iron pipe provided with screw caps at the ends, and then 

 heated thoroughly for some time, under a power blast, in a gas furnace. 

 The pipe was surrounded by fire bricks and after the fire had been re- 

 moved it was allowed to cool for many hours with its axis perpendicu- 

 lar to the earth's meridian before the annealing process was regarded 

 as complete. In this manner most of the pieces were fairly well de- 

 magnetized. Of course, the permanent magnetic moment of an iron 

 cylinder of length only twice as great as its diameter, is never very 

 strong, but it was usually possible to detect some evidences of magnet- 

 ization in every piece tested, A stout cylinder acquires a fairly large 

 temporary moment, even when it is held with its long axis perpendicu- 

 lar to the earth's field, and it is very necessary to adjust the relative 

 positions of such a specimen and a magnetometer by which it is to be 

 tried, so that this magnetization shall not affect the measurements. 

 The short iron cylinders which von Waltenhofen used must have been 

 very soft indeed if they really lost their magnetization completely when 

 left to themselves, with their axes perpendicular to the meridian, for a 

 number of days. 



Cases of Magnetization "Which are not Really Anomalous. 



In many cases of so called " anomalous magnetization," it is evident 

 that a strong magnetizing field applied in one direction has been suc- 

 ceeded by a weaker field in the opposite direction, and when this latter 

 has been removed, the magnet has the polarity of the first field. This 

 is of course not wonderful except as we may regard all hysteresis 

 phenomena as mysterious. Figure 1 shows a hysteresis diagram for 

 an iron rod about 80 diameters long, with a number of loops corre- 

 sponding to " side trips " within the main figure. It is clear that if 

 the rod has been magnetized by a positive current so that the mag- 

 netic condition while the current is flowing is represented by the point 

 N, and if the current be then stopped so that the condition of the rod 

 is denoted by A and an oppositely directed current which gives rise to 

 a field not greater than the abscissa of the point V be applied and then 

 removed, the resulting magnetization of the rod will be represented by 

 some point of the line OA. If the negative field is greater than OC, 

 the polarity of the rod while the current is on will be negative, but if 

 it be not too strong the polarity will be positive when the field is off. 

 This phenomenon is relatively pronounced in the case of a short, stout 

 rod where OA is short and the slope of the lower side of an inner loop 



