36 



EEPOET 1879. 



II. — Wire Slowly Broken. 



It is found daring the breaking of these wires that the wire becomes 

 alternately more yielding and less yielding to stress applied. Thus, from 

 weights applied gradually between 28 lbs. and 31 or 32 lbs., there is 

 very little yielding and very little elongation of the wire. For equal 

 additions of weight between 33 lbs. and about 37 lbs. the elongation is 

 very great. After 37 lbs. have been put on, the wire seems to get stiff 

 again, till a weight of about 40 lbs. has been applied. Then there is 

 rapid running down till 45 lbs. has been reached. The wire then becomes 

 stiff again, and often remains so till it breaks. 



It is evident that this subject requires careful investigation. 



Fourth Report of the Committee, consisting of Dr. Jotjle, Professor 

 Sir William Thomson, Professor Tait, Professor Balfour Stewart, 

 and Professor J. Clerk Maxwell, appointed for the purpose of 

 effecting the Determination of the Mechanical Equivalent of 

 Heat. 



There is little to be reported by the Committee this year, the work at 

 present in progress being the protracted one for supplying the means of 

 correcting errors in the determination of temperature arising from tem- 

 porary changes of the fixed points of thermometers constructed of glass. 

 The Committee have learned with pleasure that an extensive series of 

 experiments has recently been made by Professor Henry A. Rowland, of 

 Baltimore, who, being unaware of what had been done by the Committee, 

 has arrived at an equivalent almost identical with that determined by 

 Dr. Joule. 



