XIV. Experiments on the refrangibility of the invisible rays of the sun

Journal Article 1 Mention

William Herschel•1800

Low Citations · 8th Percentile

216 citations · Astronomy and Astrophysics

TLDR

This paper shows that sunlight contains invisible rays that can heat things up, even though we can't see them with our eyes.

Summary

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1 Study Aim

The main goal of this paper is to investigate whether the heat from sunlight includes rays that are invisible to the human eye, and to determine if these invisible rays can be bent (refracted) by a prism in the same way as visible light. The author wants to find out if the range of these heat-carrying rays extends beyond the colors we can see. Simply put: The study wants to see if sunlight has invisible parts that can be bent like visible colors and if these parts carry heat.

2 Study Design

The author describes a series of experiments using a prism to split sunlight into its different colors on a piece of white paper. He marks lines on the paper to measure where the different colors fall. He then uses thermometers to measure the temperature at different spots, including areas beyond the visible red light. By comparing the temperatures, he checks if there is heat in places where no visible light appears. Simply put: The researcher shines sunlight through a prism and uses thermometers to see if there is heat where we can't see any color.

3 Findings

The experiments reveal that the highest temperature is found just beyond the red end of the visible spectrum, where no light is seen. This shows that there are invisible rays in sunlight that carry heat, which the author calls 'calorific rays' (heat rays). These rays can be bent by a prism, just like visible light. The findings suggest that sunlight contains more than just the colors we see; it also has invisible rays that can warm objects. The author recommends further study of these invisible rays to better understand their properties and effects. Simply put: The study finds that sunlight has invisible heat rays that can be bent by a prism and make things warm, even though we can't see them.

Abstract

In that section of my former paper which treats of radiant heat, it was hinted, though from imperfect experiments, that the range of its refrangibility is probably more extensive than that of the prismatic colours; but, having lately had some favourable sunshine, and obtained a sufficient confirmation of the same, it will be proper to add the following experiments to those which have been given. I provided a small stand, with four short legs, and covered it 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 ¼ of an inch from the edge. These lines I intersected at right angles with three others; the 2d and 3d whereof were, respectively, at 2½ and at 4 inches from the first.

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