<P> The IUPAC recommended symbol for mass and charge are m and Q, respectively, however using a lowercase q for charge is also very common . Charge is a scalar property, meaning that it can be either positive (+) or negative (−). The Coulomb (C) is the SI unit of charge; however, other units can be used, such as expressing charge in terms of the elementary charge (e). The SI unit of the physical quantity m / Q is kilogram per coulomb . </P> <P> The units and notation above are used when dealing with the physics of mass spectrometry; however, the m / z notation is used for the independent variable in a mass spectrum . This notation eases data interpretation since it is numerically more related to the unified atomic mass unit . The m refers to the molecular or atomic mass number and z to the charge number of the ion; however, the quantity of m / z is dimensionless by definition . An ion of 100 atomic mass units (m = 100) carrying two charges (z = 2) will be observed at m / z = 50 . </P> <P> In the 19th century, the mass - to - charge ratios of some ions were measured by electrochemical methods . In 1897, the mass - to - charge ratio of the electron was first measured by J.J. Thomson . By doing this, he showed that the electron was in fact a particle with a mass and a charge, and that its mass - to - charge ratio was much smaller than that of the hydrogen ion H. In 1898, Wilhelm Wien separated ions (canal rays) according to their mass - to - charge ratio with an ion optical device with superimposed electric and magnetic fields (Wien filter). In 1901 Walter Kaufman measured the increase of electromagnetic mass of fast electrons (Kaufmann--Bucherer--Neumann experiments), or relativistic mass increase in modern terms . In 1913, Thomson measured the mass - to - charge ratio of ions with an instrument he called a parabola spectrograph . Today, an instrument that measures the mass - to - charge ratio of charged particles is called a mass spectrometer . </P> <P> The charge - to - mass ratio (Q / m) of an object is, as its name implies, the charge of an object divided by the mass of the same object . This quantity is generally useful only for objects that may be treated as particles . For extended objects, total charge, charge density, total mass, and mass density are often more useful . </P>

Who is credited with first measuring the charge of the electron
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