Magnetization and Magnetic Change of -Length. 549 



Our specimens consisted o£ five ferromagnetic metals, and 

 twelve specimens of nickel-steels, kindly placed at oar dis- 

 posal by M. Ch. Ed. Gruillaume. They were all examined 

 in the form of ovoids (major axis = 20 cm. and minor axis 

 = 1 cm.). 



In the first series of experiments, the specimens were first 

 annealed for about 4 hours at 1000° C. to 1100° C. in a 

 charcoal fire, after being well wrapped in asbestos, and were 

 then gradually cooled. These annealed specimens were tested 

 at the ordinary temperature, then at that of liquid air, and 

 lastly again at ordinary temperature. In the second series 

 of experiments, the measurements were always commenced 

 with freshly annealed ovoids. Lastly, in the third series, 

 all specimens were cooled in liquid air for about 15 or 

 20 minutes. The measurements at the ordinary, and then 

 at higher temperatures, were carried out ; measurements 

 were also made at different descending temperatures down 

 to the ordinary. Thus all the measurements, when set down 

 in order, form a complete cycle with regard to temperatures, 

 whose limits lie between liquid air temperature and 1200° C. 

 The methods and the results of the experiments are given 

 in the following pages. 



1. First Series. 



The apparatus for measuring the change of length was 

 similar to that used in our former experiments above referred 

 to. The ends of the ovoid to be tested were soldered to two 

 short brass rods, each end of the ovoid entering about 2 mm. 

 into the rod. The upper piece is con- 

 nected with a wire stretched vertically, 

 and the lower piece is screwed to the 

 bottom of the specimen-holder, as shown 

 in the annexed cut. The axis of the ovoid 

 can be adjusted by three small screws. 

 The holder was made of a copper tube, 

 with three long slits, equally distant from 

 one another, along its axis. These slits 

 permit the adjustment of the specimens to 

 the axial line of the tube. The rest of 

 our apparatus was exactly the same as in the former ex- 

 periment. 



In the present experiments, the magnetization was, at the 

 same time, measured by the magnetometric method. The 

 magnetometer consisted of a bell-shaped magnet suspended 



