Cavallo's multiplier
Encyclopedia
Natural philosophy
Natural philosophy or the philosophy of nature , is a term applied to the study of nature and the physical universe that was dominant before the development of modern science...
Tiberius Cavallo
Tiberius Cavallo
Tiberius Cavallo was an Italian physicist and natural philosopher.-Life:He was born at Naples, where his father was a physician....
. Its purpose was to multiply, or amplify, a small electric charge
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
to a level where it was detectable by the insensitive electroscope
Electroscope
An electroscope is an early scientific instrument that is used to detect the presence and magnitude of electric charge on a body. It was the first electrical measuring instrument. The first electroscope, a pivoted needle called the versorium, was invented by British physician William Gilbert...
s of the day. Repeated operation of the device could produce voltages high enough to generate sparks.
Description
Cavallo described his machine in his 1795 Treatise on Electricity. He had examined BennetAbraham Bennet
Abraham Bennet FRS was an English clergyman and physicist, the inventor of the gold-leaf electroscope and developer of an improved magnetometer...
's charge doubler of 1787 and found it wanting in several regards, notably in its inconsistent operation and tendency to retain the charge from an earlier experiment. Cavallo resolved to build a better device. His machine consisted of four metal plates supported on a wooden board by posts, of which three were insulating
Electrical insulation
thumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...
and one conducting.
The charge to be multiplied was applied to the first of these (plate A), which stood on an insulating post. A moveable insulated metal plate (B) was brought close to A (though not permitted to touch it), and then grounded
Ground (electricity)
In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....
. The charge on A caused charge separation on B due to electrostatic induction
Electrostatic induction
Electrostatic induction is a redistribution of electrical charge in an object, caused by the influence of nearby charges. Induction was discovered by British scientist John Canton in 1753 and Swedish professor Johan Carl Wilcke in 1762. Electrostatic generators, such as the Wimshurst machine, the...
. Plate B was then moved away, breaking its earth connection. Since B was insulated, it acquired and retained a small charge opposite in sign to the charge on A. Plate B was transferred by means of an insulating rod to be brought into electrical contact with the third metal plate C which was insulated. Since both B and C were conducting
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
, B would transfer a portion of its charge to C. To maximise the transferred charge, C was placed in close proximity to a final metal plate D, which was earthed.
The experimenter would move Plate B repeatedly back and forth, placing it near to A and earthed at one end of its motion, and then into contact with C at the other. With each cycle, charge was drawn from the Earth and added to C. After a suitable number of cycles, the grounded plate D would be removed, and the electrostatic potential on C would rise to approximately the potential of A multiplied by the number of operations.
Cavallo termed his device a multiplier, though 'addition' was perhaps a more accurate description of its operation, as the charge on C was accumulated by successive additions.
Wilson's machine
Wilson's machine, described by its inventor in Nicholson's Journal in August 1804, was a development on this concept which simultaneously operated two Cavallo's multipliers by means of a pair of reciprocatingReciprocating motion
Reciprocating motion, also called reciprocation, is a repetitive up-and-down or back-and-forth motion. It is found in a wide range of mechanisms, including reciprocating engines and pumps. The two opposite motions that comprise a single reciprocation cycle are called strokes...
levers. One side would accumulate the charge of the other, and since the two accumulating plates were connected together by means of a wire, Wilson's machine was a true multiplier, rather than an addition machine. The charge would thus accumulate more rapidly than Cavallo's multiplier and the machine could generate high voltages in a short period of time. It moreover was self-exciting, needing no initial charge to operate, as the small initial charge acquired from contact electrification
Contact electrification
Contact electrification is an obsolete scientific theory from the Enlightenment that attempted to account for all the sources of electric charge known at the time. In the late 18th century, scientists developed sensitive instruments for detecting 'electrification', otherwise known as electrostatic...
was enough to start the accumulation process.