Biography of Leopoldo Nobili

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Leopoldo Nobili was an Italian physicist who carried out early research into electrochemistry and thermoelectricity. He invented a thermopileused in measuring radiant heat, and the astatic galvanometer.

Nobili was born in Trassilico in 1784. After finishing military school“Genius” in Modena, Nobili became an artillery officer. He participated in the Napoleon campaign in Russia, in which he was honored with the orden of “Legion d’ Onore”. In 1825 Nobili invented the astatic galvanometer, fundamental instrument in the history of electromagnetism. In 1826 he developed together with Melloni a thermoelectrical battery. In 1832 Nobili was appointed as a professor of physics in the the Regal Museum of Physics and Natural History of Florence, where, in collaboration with Vincenzo Antinori (director of the Museum from 1829), he performed numerous experiments on electromagnetic induction recently discovered by Faraday.

Nobili also performed study in thermoelectricity and invented athermopile used in measuring radiant heat. A thermopile is a device that allows detection of weak sources of infra-red radiation using the thermo-electric effect.The Danish physicist Oersted and the French physicist Fourier invented the first thermo-electric pile in circa 1823 by working with pairs of small antimony and bismuth bars welded in series.

In 1829 Nobili designed a new instrument for the measurement of thermicradiations, a sort of “electric thermometre” that, following improvements by Melloni, accounted for a crucial technological innovation that allowed for a correct theoretical interpretation of thermic radiation. The new device consisted of a thermopile connected in series to the clips of the astatic galvanometer, which was also created by Nobili. He called it thermomultiplier or electric thermoscope. For most of the 19th century the thermomultiplier proved to be an irreplaceable instrument in the study of thermic radiation for its high reactivity and quickness.

This figure shows an original sketch of such an instrument after N. Nobili (1835). Due to the large thermal masses it was very slow in following signal changes. As can be imagined, these instruments were originally only applicable for laboratory work. In series connected thermocouples made of antimony and bismuth (a) form a thermopile (b). After N. Nobili (1835).

Nobili’s thermopile

This instrument is signed by the Neapolitan mechanician Filippo De Palma.

A brass base and a brass stem, the height of which could be adjusted through a ring screw locking nut, support the pile, which is inside a brass box with two binding posts at each side, which are fitted into twoinsulating bone sheets; at the top of it there are locking screw nuts that allow for the fixing (both in the front and in the back) of the brass thermic radiation collectors. The thermopile is made up of 30 pairs of thin sheets of different metal, most likely constantan copper. They are parallel and connected in series through weldings at their ends, so that all the even (upper) order weldings are on one extremity and all the uneven (lower) order weldings are on the other extremity.

The series of sheets, which are dipped into an insulating putty, form a small parallelepiped enclosed in a brass case. The two plain faces are uncovered and they are respectively obtained by the alignment of the even ordered and of the uneven ordered weldings. The ends of the weldings are linked to the terminal posts. A truncated cone brass collector with a door, which is also a good screen against possible secondary external sources, conveys the “radiant heat” to the even ordered surface. The other surface is enclosed in a second (smaller) box-shaped collector with a door.

The truncated-cone collector is placed in front of the heat source to be measured and the rheofores of the astatic galvanometer are connected to the terminal posts of the thermomultiplier. If the heat radiation of the source is of low intensity one can find an approximate direct proportionality between the degrees of the angular deflection of the galvanometer’s needle and the difference in temperature between the opposite weldings of the pile. If the heat radiation is more intense the proportion is more complex. In the second half of the 19th century the makers often provided each multiplier with a table, on which the intensity was expressed in degrees, indicating the existing relation between needle deflection and the constant intensity of thermic radiation.

However, the most important his contribution to electrical science was an astatic galvanometer. The first galvanometers, called simple galvanometers, were not shielded from terrestrial magnetic field, so when the electric current was running inside, on their needle there were the effects of two magnetic fields: the magnetic field produced by instrument’s electromagnet and the terrestrial one. That was obviously involving an error in measure.

Leopoldo Nobili, the inventor of the precision galvanometer, provided the galvanometer with a system able to remove the perturbation produced by the terrestrial magnetic field using the so-called astatic system. This galvanometer uses a mobile magnet. The current to be measured runs through a fixed circuit and acts on the mobile magnet. The astatic system was an ingenious contrivance which increased the sensitivity of galvanometers by the combination of two effects: a more intense deviation power and a weakening of the opposing effect of the earth’s magnetic field.

The first astatic galvanometer was presented by Nobili in May, 1825 at the Italian Society of Science at Modena. With this model Nobili improved the precision of the galvanometer considerably and he definitely favoured the development of delicate scientific research particularly in the field of electrophysiology and thermoelectricity. Nobili, in 1827, using his newly refined galvanometer which corrected for the earth’s magnetic field, was the first to report measuring the current in a frog using any kind of an instrument. This galvanometer was also used to measure hydroelectric currents. It is important saying that at the epoch the astatic galvanometers built by Nobili were exceptional and innovative tools. The purchase of such a tool from the inventor represented a real “scientific investment” wanted by the School to keep up the pace with the new discoveries and with the new scientific instruments.

Nobili’s Astatic Galvanometers

(However, the astatic galvanometers shown here are quite different from the original prototype developed by Nobili in 1825.)

The design of the galvanometer is identical to that created by the physicist Leopoldo Nobili in 1828. This is, however, the “portable” model which is smaller, simplified and, therefore, easily handled and transported. The circular mahogany base of the galvanometer is provided in its lower part and in its inner part with a lead ring that increases the stability of the instrument. Brass foot screws at the base of the device allow for appropriate levelling.

Two small brass gudgeon-pins can be inserted into two holes at the base and two copper wire coils insulated by green silk are still wrapped around them. The gudgeon-pins act as binding posts. In the centre of the base there is a rectangular brass frame around which a coil of copper wire is wrapped. The coil is insulated by thin yellow ochre silk. In the upper part of the coil is a rhomb-shaped opening allowing for the insertion of the lower needle of the astatic system. Above the coil, horizontally, there is the silver-plated quadrant of the galvanometer with a similar rhomb-shaped opening and a graduated scale engraved upon two concentric circular rings and divided into four quadrants that are graduated from 0o to 90o.

The inner ring has thin marks for the division into degrees; the outer ring is graduated by a mark every 5 degrees. The points of the rhomboidal opening indicate the zero value on the scale, and they are placed parallel to the wires of the coil. Near one of the 90o markings, the quadrant is covered by an ivory peg with a lower tooth that prevents the lower needle of the astatic system from oscillating beyond a certain limit and the thread from entangling. A brass knob on the side of the base permits of setting the coil and the quadrant making them rotate in relation to the mobile equipment without moving the whole instrument. This can be carried out by means of an inner rack and pinion mechanism.

A glass cylindrical bell, which is blocked by brass frames at its base, protects the instrument from external disturbances. The suspension mechanism of the mobile equipment can be vertically adjusted by rotating a small brass sphere linked to the external top of the bell. This instrument lacks the astatic system. By moving the brass knob, the scale can be adjusted so that the zero values correspond to the directions of the earth’s magnetic field. When inserted in series connection to an electrical circuit, the device gives a direct proportion (for slight deviation of the needle: up to 25o) between the angle and the intensity of the current.

Instruments of Nobili’s “Electromagnetic Box”

These instruments were part of a box of didactic and scientific instruments and models (called the electromagnetic box) created by Leopoldo Nobili to reproduce the main experiences of electromagnetism that were known at that time. The box, which is one of the most complete of the period, originally contained sixteen pieces; it was later enriched with additional models and instruments such as, for example, those suggested by Faraday or by Nobili himself (magnetic radiation). Unfortunately, only these four models of the original box now remain. They were listed in a catalogue of 1864, where “Firenze 1847″ is written in the margin to indicate the place of origin and the date of entry.

Nobili’s electrochromic art

In 1826 Leopoldo Nobili obtained colors of interference on metallic surfaces through electrochemical oxidation. He studied the colored surfaces and the technique to obtain them not only for scientific reasons, but also for “the advantages that these colors and new technique of coloring metals may lend to the arts”. Nobili’s work can be considered an is example of generative art.

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