I found this: physics - Origin of the coulomb and ampere - History of Science and Mathematics Stack Exchange

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my question: why is the coulomb (and ampere) the size it is today, which an outrageous size that makes it impractical for direct use?

The coulomb has that value because in the mid 19th century electrical engineers needed practical units for submarine cables and telegraphy.

In 1861 a committee of the British Association for the Advancement of Science was appointed to propose a system of units that included electrical and mechanical units. The committee defined two coherent systems for scientists, called electromagnetic and electrostatic units, and added several “practical” units that were decimally compatible with the electromagnetic units, for the electrical engineers involved in telegraphy and submarine cables.

In 1861 the electrical engineer Latimer Clark suggested to the committee that practical voltages were in the range of 1 to 10^6 volt, resistances of conductors and insulators were in the range of 1 to 10^8 ohm, and the smallest current was about 10^-3 ampere (translated to modern units). He proposed names like volt and ohm for these practical units, and the prefix mega for 10^6. The unit of charge was unimportant for submarine cables and telegraphy, so nobody cared about its practical value, it merely had to be coherent with the unit of current.

In 1881 the International Metre Convention adopted the practical units and their names: volt, ohm, and ampere. These practical units are the ones that scientists and engineers are using today."

This person seems to be saying that the definitions of a volt and an ohm were decided first, and the the coulomb was made to fit. So a coulomb is the number of electrons such that 1J applied to them fit the kind of numbers these people were looking for?

However, we also see this: “The ampere was originally defined as one tenth of the unit of electric current in the centimetre–gram–second system of units. That unit, now known as the abampere, was defined as the amount of current that generates a force of two dynes per centimetre of length between two wires one centimetre apart. The size of the unit was chosen so that the units derived from it in the MKSA system would be conveniently sized.”

This paragraph is too much for me, and assumes quite a lot on the part of the reader. Can someone tease this apart? Which one is the original basis for C? Thanks.