OCR Text |
Show WONDERFUL SILK OF SPIDER. Withstand Heat That Crack Lensea of a Micrometer. Tho astronomer nfter the t-xper-lenco of many years has found that tho spider furnishes tho only thread which can bo successfully used In carrying on his work. The spider lines mostly used aro from one-fifth to one-seM-nth of a thousandth .f an Inch In diameter, and, In addition to their strength and elasticity, they have tho peculiar property of withstanding gi.-at changes of temperature, and often when measuring the situ spots, although al-though the heat Is so Intense nn to crack the lenses of the micrometer eyepiece, et the spider lines are not In the lcRst Injured. The 'threads of the silkworm, although al-though of gtoat value as a rotumer-elal rotumer-elal product, are so coarse and rough compared with the silk of the spider that they uinnot ho used In such Instruments. In-struments. Spider lines, although but a fraction frac-tion of a thousandth of an Inch In diameter, me made up of several thousands of mli'ioscople stieams of fluid, which unite and form a single line, and It Is because of this that they rciunln true and round under tho highest magnifying power. An Instance of the durability of tho spider lines Is found at the Alleghany observatory where tho same et of lines in the tulcromoter of tho transit Instrument has been In use slnco 1SG9. |