Changes of Molecular Configurations. 



195 



catch-board EF of the trap-door BB was jerked away, by aid 

 of a rope tied at E and manipulated by an assistant.* Simulta- 

 neously with the stretching I read off the temperature-increment 

 in terms of the excursion of the needle of a sensitive mirror- 

 galvanometer, and as soon as this was taken, I made the final 

 length measurement with the cathetometer. From these both 

 dZ and dl, i. e. the length-increment of the whole wire and of 

 the part between the fiducial marks, respectively, were derived. 



oL varied between 8 cra and 20 cm , 81 between 6 cm and ll cm , L 

 being about 12 cm . 



3. In Table 1, 1 have systematized the results of the measure- 

 ments. Here p s and p h denote the radii of the wire before and 

 after straining, and are computed from gravimetric measure- 

 ments. P is the stretching force ; dl/l the longitudinal exten- 

 sion produced, and measured between fiducial marks on the 

 wire with the cathetometer. E = PdL/L = Pdl/l is the work 

 done on centimeter of length ; t the observed increment of the 

 temperature of the wire resulting. Finally r = Et/E indicates 

 the part of the applied work which is converted into heat, the 

 remainder (E—E t )/E being potentialized. The table contains 

 both PdL/L, and Pdl/l, the latter being usually greater in con- 

 sequence of errors of experiment which need not here be con- 

 sidered. 



The heat corresponding to t° being Amct, where A is the 

 mechanical equivalent of the water-gram-degree in ergs, m the 

 mass of the wire per centimeter and c its specific heat. I was 

 obliged to take c from tables and also for want of data to dis- 

 regard the variations of c during straining. Density, J, was 

 measured before and after stretching. 



Table 1. — Unergy potentialized ir 



tensile strains. First method. 





Metal 



2p, 

 2ph 



P 



61/1 



P6L/L 



Pdl/l 



t 



\/E 





cm 



9 



(cm) 



megalergs 



megalergs 



°C 





Brass 



•1662 



60,000 



•129 



7-5 



7-7 



4-3- 



0-40 



A =8-42 



•1546 





•163 



9-3 



98 



4-1 



•30 









•151 



90 



9-1 



3-9 



•31 









•168 



9-9 



10-1 



4-3 



■31 









•153 



9-1 



9-2 



6-0 



•45 









•160 



8-9 



9-6 



7-0 



•52 



Mean 







•154 



8-95 



9-24 



4-9 



•38 



Iron 



•1362 



50,000 



■087 



4-26 



4-35 



3-8 



047 



A =7-68 



•1310 





•091 



4-33 



4-56 



4-0 



•47 









•084 



4-17 



4-22 



4-3 



•54 









•087 



4-26 



4'36 



3-5 



■43 



Mean 







•0875 



4-25 

 5-58 



4-37 



3-9 



•48 



Copper 



•1630 



40,000 



•147 



5-88 



6-0 



0-77 



A =8-87 



•151.4 





•148 



551 



5-92 



5-1 



•65 









breaks 







5-5 











•153 



5-90 



642 



5-3 



•65 



Mean 







•149 



5-66 



5-98 



5-5 



•69 



* Mr. Ernest L. Howard had the goodness to give me much efficient service 

 during the course of the present experiments. 



