1825.] Philosophical Transactions for 1824, Part II. 22l2 



temper does not alter the elastic force of steel; and your Expe- 

 riments on Vibration led to the same conclusion (Nat. Philos, 

 ii. 403). But the subject appeared to require further investiga- 

 tion, and particularly because it afforded an opportunity of ascer- 

 taining some other facts respecting steel, which had not been, 

 before examined. 



" In making the experiments which I am about to describe, 

 each bar was supported at its ends by two blocks of cast iron... 

 These blocks rested upon a strong wooden frame. The scale 

 to contain the weights was suspended from the middle of the 

 length of the bar, by a cylindrical steel pin of about fths of an 

 inch in diameter. And as in experiments of this kind it is desi- 

 rable to have the means of raising the weight from the bar, with- 

 out altering its position, in order to know when the load is; 

 sufficient to produce a permanent change of structure, I have a. 

 powerful screw with a fine thread fixed over the centre of the; 

 apparatus, by which the scale can be raised or lowered, when 

 the cords on which the screw acts are looped on to the cross piit 

 by which the scale is suspended. 



'* To measure the flexure, a quadrantal piece of mahogany is. 

 fixed to the wooden frame ; two guides are fixed on one edge of 

 the mahogany, in which a vertical bar slides, and gives motion, 

 to an index. The bar and index are so balanced, that one end. 

 of the bar bears with a constant pressure on the specimen, and 

 the graduated arc over which the index moves is divided into 

 inches, tenths, and hundredths ; and thousands are measured by 

 a vernier scale on the end of the index. There is a screw at 

 the lower end of the vertical bar, by which the index is set to 

 zero, when necessary. 



"The first trials were made with a bar of bhstered steel of a 

 very good quality. It was drawn out by the hammer to the 

 width and thickness I had fixed upon, and then filed true and 

 regular. It was then hardened, and tempered to the same 

 degree of hardness as common files. 



** The total length of the bar was 14 inches; the distance 

 between the supports 13 inches ; the breadth of the bar 95 

 inches, and the depth 0-375 inches ; the thermometer varied 

 from bb'^ to 57° at the times of trial. 



lbs. inches. 



" With a load of 54 the depression in the middle was 0*02 



82 0-03 



110 0-04 



The last load remained on the bar some hours, but produced no 

 permanent alteration of form. 



" riie temper of the bar was then lowered to a rather deep 

 straw yellow, and it was tried again ; when the same loads pro- 

 duced exactly the same flexures as before. v ..^ 



