116 



Messrs. F. C. Calvert and R. Johnson on the 



and 1-25 millim. or 0049 of an inch 

 wide at the point which bears on the 

 piece of metal, Z, to be experimented 

 on, and this is supported on a solid 

 piece of iron, G. The support or 

 point of resistance, W, is lowered or 

 raised by the screw M ; and when, 

 therefore, this screw is turned, the 

 whole of the weight on the lever is 

 borne by the support I and the screw 

 M . When it is necessary, by turning 

 the screw M, the weight on the lever 

 is re-established on the bar, and ex- 

 perimented upon. 



When we wished to determine the 

 degree of hardness of a substance, we 

 placed it on the plate G, and rested 

 the point F upon it, noticing the 

 exact mark on a on the bar A, and then gradually added 

 weights on the end of the lever, C, until the steel point, F, en- 

 tered 3-0 raillims. or 0-128 of an inch during half an hour, and 

 then read off the weight. A result was never accepted without 

 at least two experiments were made, which corresponded so far 

 as to present a difference of only a few pounds. The following 

 Table gives the relative degree of hardness of some of the more 

 common metals. We specially confined our researches to this 

 class, wishing the results to be practically useful to engineers and 

 others who have to employ metals, and often require to know the 

 comparative hardness of metals and alloys. 



* This wrought iron was made from the above-mentioned cast iron. 



