£2 INSTRUMENT FOR MEASURING TENACITY* 



small proportions, as not in most instances to exceed what 

 was absolutely necessary to effect the required purpose. 

 The spring I began therefore to consider, that the employment of a 



defective* spring might be more effectual for my purpose than weights. 

 I according tried a common spring steelyard, which, 

 however, I found objectionable, from the difficulty of noting 

 the breaking point precisely on the graduated slide, by 

 reason of its being instantantaneously carried back by the 

 recoil of the spring : an objection affecting the accuracy of 

 the experiment as materially as that above stated against . 

 the weights. 

 A screw com- After a little farther consideration on the subject, I con- , 

 stirin* effec- t*i v ©d a method of combining a screw with the spring, in a 

 tuah way which I have found effectually to give a force capable 



of being approximated to the required point by the most 

 uniform and gradual increments ; constituting thereby an 

 experimental accuracy, which I believe impossible to be 

 obtained from weights however applied. 



In this arrangement, by the rotary motion of the screw, 

 an index is moved round a quadrantal scale, graduated with 

 )bs. and their decimal parts; and this index remaining 

 stationary at the breaking point, an accurate indication of 

 the quantity of force is obtained, and can be noted at 

 pleasure. 

 The principle This contrivance being considered capable of an extensive « 

 of extensive and useful application, is the reason I solicit its publicity 

 ^plication. through the me dium of your Scientific Journal. 



The whole of the Smicrologometer is represented in the 

 annexed drawing, which I hope will be rendered intelligible 

 by a short explanation. 

 Tlie apparatus Fig 1, Plate III, is a perspective view. — AA a piece of 

 ascribed. w00< 3 f any required length and thickness, at one extremity 

 of which is screwed the brass plate BB. On this are fixed 

 the two standards CC ; and into these is pivotted the endless 

 screw rf, furnished with the nut e, which, on turning the 

 screw by the micrometer heady, moves backward and for- 

 ward at pleasure. 



This nut has a slider g attached to it under the screw, 

 and passing through a hole in the standard C, in which it 

 slides freely as the nut is moved.-— h, an immovable round 



piece 



