Show WONDERFUL SILK OF SPIDER withstands heat ThaC acks lenses of a micrometer the after he exper lence of many years has found that the furnishes the only thread which can be successfully usei in carrying on his work the spider lines mostly used are from one fifth to one seventh of a thousandth of an inch n diameter and in addition to their strength and elasticity they have the peculiar property of withstanding great changes of temperature and often when measuring the gun spots al though the heat la so intense as to crack the lenses of the micrometer eyepiece yet the spider lines are not in the least injured the threads of the silkworm al though of great value as a commer caal product are so coarse and rough compared with the of the spider that they cannot he used in such in st spider lines although but a trac alon of a thousandth of an inch in diameter are made up of several thousands of microscopic streams of fluid which unite and form a single line and it Is because of this that they remain true and round under the highest magnifying power an instance of the durability of the spider lines Is found at the allegheny alleghany Alleg hany observatory where the same set of lines in the m promoter cro moter of the transit instrument has been in use since 1859 |