INDUSTRIAL PROGRESS DURING THE YEAR 1874. clxxxi 



and increase. In an elaborate discussion of the Mechanical 

 Properties of Materials of Construction, Professor Thurston 

 explains the elevation of the limit of elasticity by a continued 

 strain, which the foregoing experiments demonstrate, in the 

 following manner: "The cause is probably a gradual release 

 of internal strain. . . . The manner in which this reduction of 

 internal strain occurs, by continued stress at the limit of elas- 

 ticity, as here observed, may be readily conceived. When 

 the metal is thus strained, many sets of molecules are placed 

 in positions in which they exert a maximum effect tending 

 to produce molecular changes which may equalize the origi- 

 nally irregular distribution of inter-molecular stresses. After 

 a time the change actually takes place by " flow," and the 

 resisting power of the piece becomes increased, and its limit 

 of elasticity raised, simply because its forces are now no 

 longer divided, and may act together in resisting external 

 forces." This explanation is eminently rational, and derives 

 additional interest from Commander Beardslee's experiment- 

 al confirmation of the fact, deducible therefrom, that this re- 

 lease of internal strain occurs to a nearly equal extent if the 

 strained piece is simply laid aside for a similar interval after 

 it has been given a set. 



The interest and importance attaching to the discovery 

 of the principles above enunciated to the engineering pro- 

 fession, and to science in general, can not be overestimated. 



It is of incidental interest to note also that, at the sug- 

 gestion of Professor Thurston, the trustees of the Stevens 

 Institute of Technology have authorized the establishment 

 in connection with that institution, of a laboratory devoted 

 to technical research, designed especially to meet the neces- 

 sities of the industrial interests of the country. The labor- 

 atory, it is decided, will be devoted exclusively to the con- 

 duct of researches of a practical bearing upon the arts and 

 manufactures such, for example, as the determination of 

 the strength and other physical characteristics of materials 

 of construction, the value of fuels, of lubricants, etc. 



Especially worthy of record in our summary of technical 

 progress for the year are the highly interesting experiments 

 that have recently been made in the Assay Department of the 

 United States Mint at Philadelphia, by Mr. Alexander E. Out- 

 erbridge, to ascertain the practicability of assaying metals 



