Neviditelné světlo

Přečtěte si článek o objevu neviditelného světla a poté odpovězte na následující otázky:

1. Popište uspořádání Herschelova experimentu. K čemu slouží druhý a třetí teploměr?
2. O kolik stupňů se zvýšila teplota na prvním teploměru, když byl umístěn za červenou barvou viditelného spektra? Je z úryvku jasné, v jakých jednotkách byla teplota Herschelem měřena? Dokážete to alespoň odhadnout?
3. Vysvětlete, co vedlo Herschela k názoru, že ve spektru je za viditelným zářením nějaké další neviditelné záření.

Experiments on the Refrangibility of the Invisible Rays of the Sun
(by William Herschel)

I provided a small stand, with four short legs, and covered with white paper. On this I drew five lines, parallel to one end of the stand, at half an inch distance from each other, but so that the first of the lines might only be 1/4 of an inch from the edge. These lines I intersected at right angles with three others; the 2^d and 3^d whereof were, respectively, at 2½ and at 4 inches from the first.

The same thermometers that have before been marked No. 1, 2, and 3, mounted upon their small inclined planes, were then placed so as to have the centres of the shadow of their balls thrown on the intersection of these lines. Now, setting my little stand upon a table, I caused the prismatic spectrum to fall with its extreme colour upon the edge of the paper, so that none might advance beyond the first line. line. In this arrangement, all the spectrum, except the vanishing last quarter of an which served as a direction, passed down by the edge of the stand, and could not interfere with the experiments. I had also now used the precaution of darkening the window in which the prism was placed, by fixing up a thick dark green curtain, to keep out as much light as convenient.

The thermometers being perfectly settled at the temperature of the room, I placed the stand so that part of the red colour, refracted by the prism, fell on the edge of the paper, before the thermometer No. 1, and about half way, or 1¼ inch, towards the second: it consequently did not come before that, or the 3^d thermometer, both which were to be my standards. During the experiment, I kept the last termination of visible red carefully to the first line, as a limit assigned to it, by gently moving the stand when required; and found the thermometers, which were all placed on the second line, affected as follows.

Here the thermometer No. 1 rose 6½ degrees, in 10 minutes, when its centre was placed ½ inch beyond the visible light.

In order to have a confirmation of this fact, I cooled the thermometer No. 1, and placed No. 2 in the room of it: I also put No. 3 in the place of No. 2, and No. 1 in that of No. 3; and, having exposed them as before arranged on the second line, I had following result. […]