322 QUARTZ FIBERS. 



So uniform are the quartz fibers that the spectrum from eud to end 

 consists of parallel bauds. Occasionally a fiber is found which presents 

 a slight irregularity here aud there. A spider line is so irregular that 

 these bauds are hardly observable ; but as the photograph on the 

 screen shows, it is possible to trace them running up and down the 

 spectrum when you know what to look for. 



To show that these longitudinal bands are due to the irregularities, 

 I have drawn a taper piece of quartz by hand, in which the two edges 

 make with one another an almost imperceptilole angle, and the spec- 

 trum of this shows the gradual change of diameter by the very steep 

 angle at which the bauds run up the spectrum. 



Into the theory of the development of these bands I am unable to 

 enter; that is a subject upon which your professor of natural philos- 

 ophy is best able to speak. Perhaps I may venture to express the 

 hope, as the experimental investigation of this subject is now rendered 

 possible, that he may be induced to carry out a research for which he 

 is so eminently fitted. 



Though this is a subject which is altogether beyond me, I have been 

 able to use the results in a practical way. When it is required to place 

 into an instrument a fiber of any particular size, all that has to be done 

 is to hold the frame of fibers toward a bright and distant light, and 

 look at them through a low-angled prism. The banded spectra are 

 then visible, and it is the work of a moment to pick out one with the 

 number of bands that has been found to be given by a fiber of the de- 

 sired size. A coarse fiber may have a dozen or more, while sucli fibers 

 as I find most useful have only two dark bands. Much finer ones ex- 

 ist, showing the colors of the first order with one dark band; and fibers 

 so fine as to correspond to the white or even the gray of Newton's 

 scale are easily produced. 



Passing now from the most scientific test of the uniformity of these 

 fibers, I shall next refer to one more homely. It is simply this: the 

 common garden spider, except when very young, can not climb up one 

 of the same size as the web on which she displays such activity. She 

 is perfectly helpless, and slips down with a run. After vainly trying 

 to make any headway, she finally puts her hands (or feet) into her 

 mouth, and then tries again, with no better success. I may mention 

 that a male of the same species is able to run up one of these with the 

 greatest ease, a feat which may perhaps save the lives of a few of these 

 unprotected creatures when (piartz fibers are more common. 



It is possible to make any quantity of very fine quartz fiber without 

 a bow and arrow at all, by simpl^^ drawing out a rod of quartz over 

 and over again in a strong oxyhydrogeu jet. Then, if a stand of any 

 sort has been placed a few feet in front of the jet, it will be found cov- 

 ered with a maze of thread, of which the photograph on the screen rep- 

 resents a sample. This is hardly distinguishable from the web spun 



