Pierre Bouguer

Physicist, born in Le Croisie, NW France. In 1735 he was sent with others to Peru to measure a degree of the meridian at the equator. His views on the intensity of light laid the foundation of photometry. In 1748 he invented the heliometer.

Pierre Bouguer (February 16, 1698 – August 15, 1758) was a French mathematician and astronomer.

His father, Jean Bouguer, one of the best hydrographers of his time, was regius professor of hydrography at Croisic in lower Brittany, and author of a treatise on navigation. and two other prizes, one for his dissertation On the best method of observing the altitude of stars at sea, the other for his paper On the best method of observing the variation of the compass at sea. These were published in the Prix de l’Academie des Sciences.

In 1729 he published Essai d'optique sur la gradation de la lumière, the object of which is to define the quantity of light lost by passing through a given extent of the atmosphere, and became the first known discoverer of what is now more commonly known as the Beer-Lambert law. In 1730 he was made professor of hydrography at Havre, and succeeded Pierre Louis Maupertuis as associate geometer of the Academy of Sciences.

In 1735 Bouguer sailed with Charles Marie de La Condamine for Peru, in order to measure a degree of the meridian near the equator. Ten years were spent in this operation, a full account of which was published by Bouguer in 1749, Figure de la terre determine. In 1746 he published the first treatise of naval architecture,Traite du navire, which among other achievements first explained the use of the metacenter as a measure of ships' stability.

His name is also recalled as the meteorological term Bouguer's halo (also known as Ulloa's halo, after Antonio de Ulloa, a Spanish member of his Peru expedition) which an observer may see infrequently in fog when sun breaks through (for example, on a mountain) and looks down-sun -- effectively a "fog-bow" (as opposed to a "rain-bow").