ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



2 53 



T)y means of a spiral screw. The foot is an exceedingly substantial flat 

 tripod. 



Elastic Limit of Metals.*— T. K. E., in an abstract of M. Fremont's 

 carefully-reasoned article, contributed to the Bulletin de la Societe 

 d" 1 Encouragement pour I Industrie Nationale,\ describes the author's 

 chief experiments and results as obtained by microscopic methods. He 

 states that M. Fremont has proved : — ■ 



1. That the theoretical elastic limit is the mean charge per unit of 

 section on which the real elastic limit is locally attained at a point of the 

 piece tried. It is not the elastic limit of the metal, but of the particular 

 piece of metal under the special conditions employed. 



2. That the proportional elastic limit is still more fortuitous. Owing 

 to compensating error, the line showing the relation between stress and 

 strain may continue to be fairly straight even above the theoretical limit. 



3. That the apparent limit is the mean charge per unit of section 

 when the real elastic limit is reached in all regions where it had not 

 previously been reached. 



4. Finally, that there is only one elastic limit of a metal, the " real 

 elastic limit," as determined by the method he indicates. The real limit 

 alone has the characters of a physical constant. The other so-called 

 limits depend upon the appearance of discontinuous deformations, the 



* Nature, No. 1786[(Jan. 21, 1904) pp. 276- 



f September, 190:! 



