Immagini

DESCRIPTION

Exhibit 618 is a Leslie light meter of which exists only the wood support, formed by a lathed wood base and thermometer support. The instrument should have been like the one in reference 1 ^[2].

This light meter designed by Sir John Leslie (1766-1832), a scottish fisicist and mathematician, expert of the theory of heat and famous for the Leslie Cube this light meter is based on the principle of the differential thermometer he discovered.

It consists of two glass bulbs (one transparent and the other darkened) connected together by a thin U-shaped tube on which is present a graduated scale. That tube is partially filled with a liquid. When it is exposed to light, the darkenede tube absorbs heat and the inside air expands forcing the liquid to move along the graduated scale. Assuming that the absorbed heat is proportional to the luminous intensity, the liquid displacement permits an evaluation of the luminous intensity.

ISCRIZIONI

1. Su una faccia del supporto sono inciso due scale graduate e il nome dello strumento: "Fotométre De L'Eslie".

BIBLIOGRAPHY

• [1] URL [ http://en.wikipedia.org/wiki/John_Leslie_(physicist) ]
• [2] John Leslie, "An experimental inquiry into the nature and propagation of heat", Edinburgh 1804

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