42 J. 0. Thompson — Law of Elastic Lengthening. 



The initial load, consisting of frame, scale-pan, damper, and 

 half the weight of the wire itself, amounted to '665 kg. This 

 was probably twice as much as was really necessary to keep 

 the wire straight. In later measurements a lighter frame was 

 used. 



Experiments with Copper Wire. 



The following is one of ten series of measurements made 

 jtfay 23rd. 



Time 4 h. V m. Thermometer-wire 540*70 



weight 





Time. 



Cath. I. 





Cath. II. 



Lengthening 



kg. 





h. m. 



mm. 





mm. 



mm. 









4 9 



554-82 









0-2 





10 



49-29 





0-15 



5-53 



0-4 





12 



43-73 





a 



11-09 



0-6 





14 



38-L4 





u 



16-68 



0-8 





16 



32-51 





it 



22-31 



1-0 





18 



2684 





0-14 



2797 



1-2 





20 



21-14 





0-13 



33-66 









22 



554-795 





0-12 







Lowering 

 4 h. 27 m. 



of zero-point, 0-025 0'03 

 Thermometer-wire 540*70 



At 4 h. 33 m., the beginning of the next series of observa- 

 tions, the zero-point had risen 0'015 mm. on account of the 

 after-effect. This was generally the case between any two 

 series. The influence of the after-effect, although rather more 

 marked here than in the case of the other metals experimented 

 upon, was not enough to affect the value of the measurements. 



On this day the temperature was remarkably constant. The 

 total steady lengthening of the thermometer-wire between 2 h. 

 50 m. and 5 h. 23 m. amounted to only 0*02 mm. 



The following table gives the results of eight successive 

 measurements made with the copper wire May 23rd. 



p- 



















Mean 



kg. 



















mm. 



0-2 



5-535 



•535 



•54 



•53 



•53 



•53 



•53 



•535 



5-533 



0-4 



11-085 



•08 



•10 



•085 



•09 



•09 



•09 



•095 



11-090 



0-6 



16-675 



•675 



•685 



•685 



•685 



•68 



•67 



•68 



16-680 



0-8 



22-31 



•305 



•31 



•31 



•30 



•31 



•31 



•31 



22-308 



1-0 



27-97 



•94 



•98 



•985 



•95 



•97 



•94 



•945 



27-960 



1-2 



33-665 



•65 



•72 



•685 



•67 



•66 



•64 



•62 



33-664 



The following table gives the mean values derived from 16 



series of measurements with copper wire. 



