334 



the silk to that extent. This apparatus being completed, several inter- 

 esting tests were made with it. Later a spring or dynamometer was 

 attached to it on the upper end ; this spring, which was extended 

 by the silk attached to it, indicated the weight corresponding to the 

 effort necessary to stretch the silk to the breaking point; it therefore 

 gave the measurement of the tenacity. By means of a very simple ar- 

 rangement the needles indicating the tenacity and the ductility re- 

 mained fixed at the point in whicli they were when the silk broke. 



It was, however, soon jierceived that this apparatus, although already 

 very satisfactory, was still capable of receiving several improvements, 

 such as a fly-wheel in i^lace of the escape-wheel, which would avoid the 

 little jerks imparted to the silk by the latter. It appeared also pos- 

 sible to avoid certain corrections necessitated b}' the presence of the 

 dynamometer which let the upjier end of the silk descend slightly as it 

 yielded to the effects of the weight. A more perfect instrument was 

 then constructed, for the details of which M. Robinet gives credit to M. 

 Lehodey, a clock maker of Paris. This instrument he called the seri- 

 meter * because, as he naively says, "it was necessary to have a name for 

 it to avoid paraphrases." 



The construction of this serimeter is shown in Fig. 74 : A B C D 

 is a box one meter and a half long. At A B is a spindle on which 

 can be placed a bobbin of the silk which we wish to test; M is a 

 clip which grasps the silk and holds it firmly. K is another clip placed 

 exactly one meter from the clip M. The clip K can slide in the groove 

 N I made in the box, and is fastened, on the interior thereof, to a weight 

 attached to an endless chain. The descent of this weight is made per- 

 fectly regular by passing the chain over a sprocket-wheel forming part 

 of a clock-work. 



As soon as the mechanism starts the weight decends, drawing the 

 movable clip K towards N and stretching the silk which is fastened to 

 it. At O there is a small and very light lever which rests against the 

 stretched silk. At the moment when the latter breaks the lever acts 

 on the fly-wheel of the mechanism, and stops it immediately. The 

 needle G is attached to the clip K and indicates on the scale GL the 

 number of centimeters and millimeters which the weight has descended 

 and the silk been stretched. 



The experimenters thus devised a method of determining the ductil- 

 ity of silk, which was found to be an excellent one when the instrument 

 was well made, ran with perfect regularity, and did not jerk the silk in 

 any way. 



But it was not thought sufficient that the serimeter should give the 

 measure of the ductility alone, it must also indicate the weight equiva- 

 lent to the effort which caused the thread of silk to break; in other 

 words, it must give the measure of the tenacity. 



Tl)is desideratum was accomplished in the following manner: The 



* Silk measurer. 



