An early treatise on the transit telescope, consisting of detailed theory and instruction for use of the apparatus, as set forth by renowned astronomer Struve while he was teaching at the Dorpat observatory in Estonia. This is the original French translation - expanded and augmented with new material - of a separately printed pamphlet by Struve, published in German in St. Petersburg 1833. This French edition corrects some of the author’s formulae and makes new comparisons between transit instruments devised and built by Troughton and by Ertel. The work reveals the scientific advances in the making of instruments that would revolutionise navigation.