384 
MR. C. CHREE ON THE EFFECTS OF PRESSURE 
1. The strengths of the fields in which the changes in the magnetisation produced 
hj the first application of a given stress, or by its cyclic repetitions, bear the greatest 
ratios to the pre-existing magnetisations, are very low, if indeed they possess a finite 
value. 
2. The fields in which the changes in the magnetisation produced by the first appli¬ 
cation of a given stress, or by its cyclic repetitions, are absolutely greatest, are not 
very far from the region of the Wendepunkt. 
3. The maximum cyclic effect appears, however, in a distinctly lower field than 
does the maximum effect of the first application of stress. 
4. Both the cyclic effect and the effect of the first application of stress possess 
critical or Villari points, and the critical magnetisations are both considerably 
greater than that answering to the Wendepunkt. 
5. The critical field, however, for the cyclic effect is decidedly lower than that for 
the first application of stress. 
6. The residual magnetisation approaches “ saturation ” in much lower fields than 
does the induced. 
7. The residual susceptibility —or the ratio of the residual magnetisation to the 
strength of the pre-existing field—when the specimen is free from stress, attains a 
maximum when the pre-existing field is very considerably lower than that answering 
to the Wendepunkt. 
8. The retentiveness —or the ratio of the residual to the induced magnetisation—in 
the absence of stress, attains a maximum in a field decidedly lower than that in which 
the residual susceptibility is a maximum. 
9. Stress increases largely the residual susceptibility and the retentiveness in weak 
fields, and decidedly lowers the fields in which these magnitudes present their 
maxima. 
§ 70. If the magnetisation answering to its Wendepunkt be taken as the unit for 
each individual specimen, the following Table gives approximately the induced magne¬ 
tisations existing during certain critical events in the magnetisation of the cobalt rod, 
and three samples of stretched iron wire examined by Professor Ewing. 
Table XI. 
Maximum 
Retentiveness. 
Maximum 
residual susceptibility. 
Critical point 
for cyclic effect. 
Critical point 
for first stress. 
Cobalt .... 
•40 
•58 
2-31 
2-53 
1st iron wire . 
1-60 
1-87 
2n(l „ . . 
•53 
•70 
3rd „ . . 
•55 
•70 
This will serve to show the kind of evidence on which the above statements as to 
the relations between cobalt and iron are based. Considering also that the intensities 
