fur Measuring the Expansions of Soli Js, S;c. 271 



If from the real expansion thus obtained •0194.7 



we deduct the apparent expansion obtained by the 



pyrometer '01163 



the remainder 'OOTS* 

 will be the expansion of the black-lead. 



T}ie Expansion of Iron. 



Length of Bar. 



From 32^0 212° = •00118203x6-5 =-007683195 



From 392° to 572° = -00146842x6-5 =-009544730 



•017227925 

 From 212° to 392° = Mean of the above =-008613962 



Total expansion from 32° to 572° =-025841887 



Add for the expansion from 572° to 660°, 

 the temperature of boiling mercury, calculated 

 at the highest rate : — 



180° : -009544730 : : 88° : -004666311 . ... =-004666311 



•030508198 

 Deduct expansion for 32°, the experiment with 



the pyrometer having commenced at 64° ... ='001365901 



Calculated at the lowest rate : — 



180° : ^007683195 : : 32° : -001365901 

 Real expansion of the bar by Dulong and Petit -029142297 



From the real expansion -02914 



deduct the apparent expansion obtained by the 



pyrometer -02036 



The remainder '00878 

 is again die expansion of the black-lead as obtained 

 by this series ofj^experiments. 



Expansion of 6-5 inches of black-lead. 



From 64° to 660° by platinum bar -00784 



by iron bar '00878 



Mean -00831 

 either determination differing from the mean by less than 

 -j-jj ^jjijdths of an inch. 



Tliis close agreement in results from two metals whose 

 expansions differ so much from each other is highly satisfac- 

 tory ; but the great delicacy of the instrument may be still 

 better appreciated from the Ibllowing experiment of the ex- 

 pansion of nine diflcrent metals from the temperature of 62° 

 (the temperature of the air at the time of observation) to212°. 



Exp. 3. 



