The tangent galvanometer of Johan Jacob Nervander

J.J. Nervander designed the more- sensitive tangent galvanometer in 1834, which led to a great improvement in precise measurements of electric current. Because of its ingenuous coiling arrangements, Nervander was able to use the tangent busol to prove the validity of the law that the tangent of the deviation angle of the needle of the tangent-bussol is proportional to the electric current flowing through its coil. Exploitation of the tangent law provided a way of measuring and comparing currents. The increased sensitivity of the galvanometer was a result of the uniformity of the current-created magnetic field over the cylindrical volume inside the coils. This allowed the use of a long magnetic needle. The reconstructed galvanometer operates with a short needle. For the reconstructed galvanometer, the tangent law is valid up to deflection angles more than 50deg; Nervander reported acceptable deviations only up to 30deg.