Biography of Horace Benedict de Saussure

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Horace-Benedict de Saussure was Swiss physicist, geologist, and early Alpine explorer who also developed probably the first electrometer, a device for measuring electric potential by means of attraction or repulsion of charged bodies.

The Saussure family, whose fame has spread in Geneva, as it has abroad, came originally from Lorraine. They sought refuge in Geneva at the time of Calvin’s reform and were accepted into the bourgeoise in 1635. Several of his sons’ names passed into posterity. Nicolas (1709-1790) shone in agronomy, Nicolas-Theodore (1767-1845) in chemistry and his son Henri (1829-1905) in entomology. But the best known were Horace-Benedict (1740-1799) and Ferdinand (1857-1913).

Horace-Benedict de Saussure was Swiss physicist, geologist and meteorolgist. He was born in Conches, close to Geneva, on February 17, 1740. In 1746, six years old, he entered the public school of Geneva. In 1754 he continiued education in the Academy (University) of Geneva. In 1759, 19 years old, Horace-Benedict de Saussure completed his studies at the Academy, by presenting one Dissertatio physica of igne. In 1762 he became professor of philosophy and natural sciences at the Academy in Geneva (of which he was rector in 1774-1775), where he founded Societepour le Avancement des Arts. In May 1765 Horace-Benedict de Saussure married Albertine Boissier.

In 1768 Saussure began his geological journeys, in the course of which he crossed the Alps fourteen times.

The word geology was introduced into scientific nomenclature by Saussure with the publication of the first volume of his Voyages dans les Alpes (1779-96; “Travels in the Alps”), a work that contains the results of more than 30 years of geologic studies.

Mountaineering in a contemporary sporting sense was born when a young Genevese scientist, Horace-Benedict de Saussure, on a first visit to Chamonix in 1760, viewed Mont Blanc (at 15,771 feet [4,807 m] the tallest peak in Europe) and determined he would climb to the top of it or be responsible for its being climbed.

Saussure offered prize money for the first ascent of Mont Blanc, but it was not until 1786, more than 25 years later, that his money was claimed by a Chamonix doctor, Michel-Gabriel Paccard, and his porter, Jacques Balmat. Saussure’s glory culminated in his own climbing Mont Blanc, whose summit he reached on 3 August 1787.

Horace-Benedict de Saussure discovered fifteen minerals, made careful measurements of atmospheric humidity, improved the thermometer and the anemometer, and developed the hair hygrometer and, probably, the first electrometer.

The first true electrometer, a device for measuring electric potential by means of attraction or repulsion of charged bodies, came from Horace-Benedict de Saussure who placed in 1766 the strings and balls inside an inverted glass jar and added a printed scale so that the distance or angle between the balls could be measured. It was de Saussure who discovered the distance between the balls was not linearly related to the amount of charge.

Later Saussure used his electrometer for various experiments with electricity. For example, the results published by Volta fired up de Saussure`s enthusiasm to investigate electricity from evaporation. His first experiment in 1786 involved throwing red hot iron into an insulatedcoffee pot containing water. His results were opposite to those obtained by Volta. So, de Saussure rearranged his apparatus to allow water to be evaporated by boiling in an insulated dish. Negative electricity was usually produced but variation of polarity did occur. Next he threw water into a dish ‘whose temperature was diminishing’ (i.e. cooling).

An iron ‘grenade’ was heated to white heat and he threw water inside. A flame issued from inside the grenade! A sheet of linen six feet square was wetted, insulated with silk cords and hung up to dry in front of a fire. A large iron plate was placed on the ground and heated so that a great quantity of steam came off.

Horace-Benedict de Saussure’s results in summary are:

1.Evaporation of water without ebullition does not produce electricity.
2.Water remaining stationary in a very hot dish (Leidenfrost’s Phenomenon) does not produce electricity.
3.Water which wets a warm surface and evaporates quietly does notproduce electricity.
4.The greatest quantity of electricity is produced when the evaporating water in making the loudest noise.
5.The electrical polarity for water evaporating from heated iron or copper dish is positive. It is negative from a silver or porcelain dish.
6.Experiments to produce electricity from combustion yielded no electricity.

Horace-Benedict de Saussure also developed an improved hygrometer to measure atmospheric humidity. It was in the 15th century when it was first observed that wool grows heavier with humidity. Later, Boyle and Goalal observed that the length of a cord from which a body is suspended varied, becoming longer the greater its humidity. These observations led to the development of absorption hygrometers, of which Saussure’s is an example.

De Saussure’s hair hygrometers

In 1783 Saussure built the first hygrometer utilizing a human hair to measure humidity. The hair hygrometer is an instrument that measures the humidity in the air (hygrometric grade). It was a type of instrument that was used widely in its time, although it was not very precise. All hairhygrometers can be considered as being derived from that of Horace-Benedict de Saussure. In this specimen, the hygrometer is inside a wooden case with a glass door, in which a mercury thermometer with a scale. The instrument can be hung on the wall with a hook.

The Saussure hygrometer in the Gabinete de Fisica was constructed in Coimbra. The following inscription can be seen on it, identifying the maker: J.J. Miranda, Coimbra. The apparatus is protected by a wooden box which has a wooden – framed glass door at the front. Its operation was based on the dilation of a strand of hair under tension, when the humidity of the air was increased. The hygrometer has three vertical shafts, two being cylindrical and the third quadrangular.

The cylindrical shafts are in the front part of the apparatus and support acircular ring 8 cm in diameter, on which a scale is engraved. This scale is divided into 360 divisions marked from 0 to 360. Each division is subdivided into 10 parts. Together with the pointer, a horizontal axle installed between the scale ring and the rear shaft, moves. On this axle, next to the face of the dial, is a threaded worm-screw, on which the strand of hair is wound in order to regulate its length.

The tension on the strand of hair can be adjusted through the action of a cord wound on the axle of the pointer. The other end of this cord is fixed on a metallic piece that enters a little cylindrical tube which is narrow inside. This cylindrical tube can move along the vertical shaft of the quadrangle, being placed in a position that keeps the strand of hair under tension. The hygrometer is calibrated by taking the two extreme situations as a reference: that of saturation by water and that of complete dehydration. For the first case, the hygrometer is placed with a receptacle of water, and covered by a glass bell jar. The dry condition is obtained by putting the apparatus under the bell jar with calcium carbonate or lime.

Horace-Benedict de Saussure died in the morning on January 22, 1799. He was buried in the cemetery of Plainpalais, Geneva.

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