442 



NATURE 



\Sept. 4, 1879 



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

 smallest weight which, applied very cautiously and with pre- 

 cautions 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 com- 

 plete them. 



The other experiments have been carried out in the following 

 ■way : — It was found that a weight of 28 lbs. does not give per- 

 manent 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 elonga- 

 tion 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 the rate of one pound 

 per day, some with three-quarters of a pound per day, and some 

 with half a pound per day. One experiment was commenced in 

 which it was intended to break the wire at a very much slower 

 rate than any of these. It was carried on for some months, but 

 the wire unfortunately rusted, and broke at a place which was 

 seen to be very much eaten away by rust, and with a very low 

 breaking weight. A fresh wire has been suspended, and is now 

 being tested. It has been painted with oil, and has now been 

 under experiment for several months. 



The following tables wiil show the general results of these 

 experiments. It will be seen, in the first place, that the pro- 

 longed application of stress has a very remarkable effect in in- 

 creasing the strength of soft iron wire. Comparing the breaking 

 weights for the wire quickly broken with those for the same 

 wire slowly broken, it will be seen that in the latter case the 

 strength of the wire is from two to ten'per cent, higher than in 

 the former, and is on the average about five or six per cent, 

 higher. The result as to elongation is even more remarkable, 

 and was certainly more unexpected. It will be seen from the 

 tables that, in the case of the wire quickly drawn out, the 

 elongation is on tlie average more than three times as great as in 

 the case of the wire drawn out slowly. There are two wires 

 for which the breaking weights and elongations are given in the 

 tables, both of them " bright " wires, which showed this differ- 

 ence -very remarkably. They broke without showing any special 

 peculiarity as to breaking weight, and without known difference 

 as to treatment, except in the time during which the application 

 of the breaking weight ivas made. One of them broke with 

 44 lbs., the experiment lasting one hour and a half; the other 

 with 47 lbs., the time occupied in applying the weight being 

 thirty-nine days. The former was drawn out by 28'5 per cent, 

 on its original length, the latter by only 479 per cent. 



TaUes showing the Breaking of Soft Iron Wires at Different 

 Speeds 

 I. — Wire Quickly Broken 



Rate of adding weight. 



Breaking 

 weight in 

 pounds. 



Per cent, of 



elongation 



■ on original 



length. 



^Dark Wire 



J lb. per minute ... 



1 „ 5 minutes 



»» 5 »i 



>> 4 >. 



j» 3 j» 



>» 3 »» 



" 5 »> 



I lb. per 5 minutes 

 »i 5 »» 

 4 „ 



' Bright Wire 



' TlJ^ wire used was all of the same qu.ality and gauge, but the "dark" 

 and bright" wire had gone through slightly different processes for the 

 purpose of annealing. 



II. — Wire Slowly Broken 



Weight added and No. of 

 experiment. 



BreaVing 



weight in 

 pounds. 



48 

 46 

 47 

 47 

 47 

 47 

 46 



47 



Per cent, of elongation on 

 original length. 



49 



48i 

 Broken by accident. 



7-58 

 813 

 7-05 

 6-51 

 8-62 



5'«7 

 5 'SO 

 6-92 Bright wire. 



8-50 



46 

 46 

 4Si 



48 

 50 

 49 

 47 

 46i 



7-SS 

 6-41 

 6-62 



8-26 

 8-42 

 7-i8 



479 

 6-00 



Bright wires. 



It was found during 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 be- 

 comes stiff again, and often remains so till it breaks. 



It is evident that this subject requires careful investigation. 



Report of the Committee for effecting the Determination of the 

 Mechanical Equivalent of Heat. — The Committee had little to 

 report this year, the work in progress being the protracted one 

 of supplying a means of correcting errors in the determination of' 

 tlie temperature arising from the temporary changes of the 

 fixed points of thermometers constructed of glass. They had 

 learned with pleasure that an extensive series of experiment.' 

 had recently been made by Prof. H. A. Rowland, of Baltimore, 

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

 had arrived at an equivalent almost identical with that determined 

 by Mr. Joule. 



Report of the Committee appointed for the Purpose of endt 

 vouring to procure Reports on the Progress of the Chief Branch, 

 of Mathematics and Physics. — Owing to unforeseen circum 

 stances no meeting of this Committee has taken place daring 

 the past year. It seems desirable, nevertheless, in order that 

 the question of the reappointment of the Committee may be 

 fully considered, and that there may be a full expression of 

 opinions on the subject referred to it, that a statement should 

 be made to the Section of the proceedings of the Committee, 

 the more so since, in the hope that greater progress would have 

 been made by this time, no report was presented at the last 

 meeting of the Association. 



The first matter discussed by the Committee was the character 

 and general plan of the reports which they should endeavour to 

 procure ; the next was to what extent or in what manner the 

 production of such reports could be aided by the Committee. 

 Important contributions to the discussion of these questions are 

 contained in written communications to the Committee from two 

 of its members, Professors Clerk-Maxwell and Stokes. Prof. 

 Clerk-Maxwell writes as follows :— 



"Reports on special branches of science may be of several 

 different types, corresponding to every stage of organisation, 

 from the catalogue up to the treatise. 



" When a person is engaged in scientific research, it is desir- 

 able that he should be able to ascertain, with as httle labour as 

 possible, what has been written on the subject and who are the 

 best authorities. The ordinary method is to get hold of the most 

 recent German paper on the subject, to look up the references 



■hl^t 



