The exemplar conserved in Cagliari was constructed by the Machinist of the Physics Laboratory and Assistant Preparer, the Cagliari-born Giuseppe Dessì. It differs from traditional tangent galvanometers in that it has two coils instead of one, they are traversed in the same direction by the current to be measured and are arranged symmetrically with respect to the centre of the magnetic needle. It can be stated with certainty that this galvanometer was assembled by Giuseppe Dessì on the suggestion of Antonio Pacinotti or his successor Enrico Campi since he, using two coils and placing them at a distance one from the other equal to the length of their radius, had designed the configuration that is created at the mean point of the segment that joins their centres and, in the vicinity, a uniform field parallel to the axis. The denomination of Helmoltz coil that was given to two coils when they are in that configuration is due to the fact that it was Hermann Ludwig Ferdinand von Helmoltz (1821-1894) who created it 1853. ...continues