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By JOHN A. BRASHEAR. In our study of the exact methods of measurement in use to-day, in the various branches of scientific investigation, we should not forget that it has been a plant of very slow growth, and it is interesting indeed to glance along the pathway of the past to see how step by step our micron of to-day has been evolved from the cubit, the hand's breadth, the span, and, if you please, the barleycorn of our schoolboy days.
Professor Schumann has succeeded in photographing them by depositing bromide of silver directly on glass plates without fixing it with gelatine; and he has, by the same process, photographed in the spectrum of hydrogen a ray with a wave-length of only 0.1 micron.
You cannot see into its substance a millionth of a micron the illusion of transparency being purely a surface phenomenon, and peculiar to this one form of substance. I have told you that the ether is a fourth-order substance this also is a fourth-order substance, but it is crystalline, whereas the ether is probably fluid and amorphous.
The only differences which subsist are necessarily those due to the considerable discrepancy which exists between the durations of the periods of these two categories of waves. The length of wave corresponding to the first spark-gap of Hertz was about 6 metres, and the longest waves perceptible by the retina are 7/10 of a micron.
The great difficulty of the experiment proceeds from the vast difference which exists between the lengths to be compared, the wave-lengths barely amounting to half a micron; the process employed consisted in noting, instead of this length, a length easily made about a thousand times greater, namely, the distance between the fringes of interference.
According to M. Blondlot the N rays can be polarised, refracted, and dispersed, while they have wavelengths comprised within .0030 micron, and .0760 micron that is to say, between an eighth and a fifth of that found for the extreme ultra-violet rays. They might be, perhaps, simply rays of a very short period.
Now modern science recognizes a long series of waves in ether, commencing with the smallest yet known measuring 0.1 micron, or about 1/254,000 of an inch, in length, measured by Professor Schumann in 1893, and extending to waves of many miles in length used in wireless telegraphy for instance those employed between Clifden in Galway and Glace Bay in Nova Scotia are estimated to have a length of nearly four miles.
"I guess you know most of the facts. They are made out of permallium. Have you ever seen any of the stuff?" The new man shook his head. "I read about it though some new alloy, isn't it?" "Plenty new. It's the hardest stuff anybody has ever made. If you set off one hundred successive atom blasts over a lump of permallium, you might crystallize and scale maybe a micron off the surface.
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