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"By using carefully selected colour screens and orthochromatic plates a perfectly legible photograph of the writing may be taken, although there may be no marks on the charred remains that are visible to the eye. This is the only known method in many cases. I have here some burned fragments of paper which I gathered up after the first attempt to fire your store, Mr. Stacey."
And since photographic refractors are corrected for the blue rays, exposures with them of orthochromatic surfaces would be entirely futile.
It made, nevertheless, capricious appearances at South Kensington during that autumn, and again October 21, 1894, while in September, 1892, Bélopolsky could obtain no trace of it on orthochromatic plates exposed with the 30-inch Pulkowa refractor. No fluctuations in the hydrogen-spectrum were betrayed by them; but subordinate lines of unknown origin showed alternate fading and vivification.
"By using carefully selected colour screens and orthochromatic plates a perfectly legible photograph of the writing may be taken, although there may be no marks on the charred remains that are visible to the eye. This is the only known method in many cases. I have here some burned fragments of paper which I gathered up after the first attempt to fire your store, Mr. Stacey."
Here were patent gimcrack printing devices, although he had scarce anything worth printing; all sorts of atrocious fancy borders with which he sought in vain to embellish out-of-focus under-exposures; orthochromatic filters and colour screens with which he was eliminating undesirable rays, although the chief thing his negatives lacked was light of any kind.
Material surfaces, it would appear, reflect them all in equal value, and the color of the resultant picture depends on the color of the foco frequencies. By altering these, a reddish, yellowish or bluish picture may be seen. In actual practice an orthochromatic mixture of frequencies is used to give a black, gray and white picture.
Upon plates rendered "orthochromatic" by staining with alizarine, or other dye-stuffs, the whole visible spectrum can now be photographed; but those with their maximum of sensitiveness near G are found preferable, except where the results of light-analysis are sought to be completely recorded.
The stars whose spectrum is known to be banded, to contain bright lines, or to be peculiar in other respects, will also be examined systematically. Experiments will also be tried with orthochromatic plates and the use of a colored absorbing medium, in order to photograph the red portions of the spectra of the bright stars. Quartz will also be tried to extend the images toward the ultra-violet.
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