312 



In silks composed of the same number of filaments the relative ductility is not pro- 

 portional to the volume. In the same silks the absolute ductility increases in a pro- 

 portion which is very small when compared with the increase in the volume. 



In silks composed of increasing numbers of filaments the elongation is not in pro- 

 portion to the volume. In the same silks the relative ductility is almost in an in- 

 verse proportion to the volumes. In the same silks the absolute ductility augments 

 to a certain degree with tlie number of filaments. These augmentations of ductility 

 are successive and show a certain degree of regularity. 



The volumes teing equal, that silk is the most ductile into the composition of 

 which enter the greatest number of filaments. In other words, given two silks of 

 the same size, if there are five filaments in one and six in the other the latter will be 

 the most ductile. 



Therefore, although augmentation in volume in silks composed of the same num- 

 ber of filaments has an almost insensible influence on their ductility, an increase in 

 the number of filaments increases the ductility to a considerable degree. This etfect 

 of the solidaritj^ of the filaments is, however, very different for the ductility and the 

 tenacity. The solidarity causes the tenacity to increase in a greater proportion than 

 the increase in the number of filaments, while the ductility does not by any means 

 increase in this proportion. 



The general conclusion which is naturally presented to the mind after having 

 thought over the facts recorded above is that silk is a much more homogeneous mat- 

 ter than was thought at first. The race of the worms, the climate, the nature of the 

 food,* nothing, in fact, appears to sensibly alter its composition and its essential prop- 

 erties. 



Whether it comes from the North or the South, from a feeble or a robust worm, 

 whether it be white or yellow, fine or coarse, brilliant or dull, we find the same com- 

 position, the same proportional strength, the same elasticity. This all depends, how- 

 ever, on one condition — ihat all the samples examined shall have been reeled under 

 the same conditions. 



Some of the influences which have been thought powerful and capable of pro- 

 foundly altering the essential properties of silk are almost powerless. Such are the 

 age of the cocoons or of the reeled silk, the nature of the reeling-water and its tem- 

 perature. On the other hand, it seems demonstrated that the processes and th? 

 mechanisms which have the effect of augmeutiug the tension of the silk thread dur- 

 ing its development may alter it in an essential manner, above all its extensibility. t 



EXTRACTS FROM CORRESPONDENCE. 



Borers in a traveling Trunk. 



Oupages258-2G2, Annual Report Commissioner of Agriculture, 1885, just received, 

 you deal with the Leather Beetle. Possibly the following which at the time was a 

 revelation to me may also interest you. In September, 1866, I bought a fine solid 

 Russia-leather trunk in St. Petersburg. The price did not seem high. It had an ad- 

 ditional outside linen cover, and I never noticed any sign of gnawing by insects. It 

 was traveling with me until January 7, 1867 ; then quiet in my paternal trunk-room 

 in New York until May, 1867; then with me. in Washington until May, 1868; then 

 with me in the old Cincinnati Observatory, Mount Adam, Cincinnati, until Novem- 

 be> , 1870. During these last two years I believe that I did not use it or move it from 



*No food but the mulberry was used. It remains to be seen if the Madura will 

 give different results. — P. W. 



t Tliese last paragraphs are quoted by M. Persoz from the second t)f a scries of 

 meni(»iis iJublisluMJ l)y M. Robinet between 1843 and 18l8. 



