34 report — 1879. 



however, can only be regarded as a temporary mode of keeping these 

 records. 



It is intended that the record in this book shall contain — 



1. Description of the tube and arrangements for suspending the wires, 

 and for suspending additional wires at future times, and description of the 

 mode of attachment of the stretching weights. 



2. Description of the cathetometer and method of measuring the 

 changes, should there be any, in the lengths of the wires. 



3. Description of the wires themselves, and record of experiments that 

 have already been made on them as to breaking weight and Young's 

 Modulus of Elasticity. 



4. Description of the marks put on the wires, and record of the mea- 

 surements that have been made as to the lengths of the wires and as to 

 the relative positions of the marks at the time of suspending the wires. 



The stretching weights and the clamps attached to the wires are en- 

 graved each with the amount of its weight in grammes. The measure- 

 ments are all made in grammes and centimetres. 



It seems desirable, considering the nature of the experiments that are 

 just now commencing, that information regarding them should be pre- 

 served to the British Association in some appropriate way ; and that pro- 

 vision should be made for recording every change that may take place, 

 and for communicating from time to time to the Association such infor- 

 mation as may be obtained. 



In the report presented to the Association by this Committee last year, 

 it was mentioned that experiments had been commenced in the laboratory 

 of the University of Glasgow in connection with the present investigation 

 on the effects of stress maintained for a considerable time in altering the 

 elastic properties of various wires. These experiments are still being 

 carried on, and results of interest and importance have been already 

 arrived at. 



The most important of these experiments form a series that have been 

 made on the elastic properties of very soft iron wire. The wire used was 

 drawn for the purpose, and is extremely soft and very uniform. It is 

 about No. 20 B.W.G., and its breaking weight, tested in the ordinary way, 

 is about 45 lbs. This wire has been hung up in lengths of about 20 feet, 

 and broken by weights applied, the breaking being performed more or less 

 slowly. 



In the first place, some experiments have been tried as to the smallest 

 weight which, applied very cautiously and with precautions against letting 

 the weight run down with sensible velocity, will break the wire. These 

 experiments have not yet been very satisfactorily carried out, but it is 

 intended to complete them. 



The other experiments have been carried out in the following way : — 

 It was found that a weight of 28 lbs. does not give permanent elongation 

 to the wire taken as it was supplied by the wire-drawer. Each length of 

 the wire, therefore, as soon as it was hung up for experiment, was weighted 

 with 28 lbs., and this weight was left hanging on the wire for 24 hours. 

 Weights were then added till the wire broke, measurements as to 

 elongation being taken at the same time. A large number of wires were 

 broken with equal additions of weight, a pound at a time, at intervals of 

 from three to five minutes — care being taken in all cases, however, not to 

 add fresh weight if the wire could be seen to be running down under the 

 effect of the weight last added. Some were broken with weights added at 



