Soon after the young ensign had entered upon his regimental duties, an affair occurred which threatened to obscure his hitherto bright prospects. His Colonel, Baron Koskull, had been disgraced by the King, about the time that he had recommended Ericsson for promotion. This circumstance induced the King to reject the recommendation. The Colonel was exceedingly annoyed by this rejection; and having in his possession a military map made by the expectant ensign, he took it to his Royal Highness the Crown Prince Oscar, and besought him to intercede for the young man with the King. The Prince received the map very kindly, expressing great admiration of its beautiful finish and execution, and presented himself in person with it to the King, who yielded to the joint persuasion of the Prince and the map, and promoted the young ensign to the lieutenancy for which he had been recommended. About the time of this promotion, the Government had ordered the northern part of Sweden to be accurately surveyed. It being the desire of the King that officers of the army should be employed in this service, Ericsson, whose regiment was stationed in the northern highlands, proceeded to Stockholm, for the purpose of submitting himself to the severe examination then a prerequisite to the appointment of Government surveyor. The mathematical education which he had received under Count Platen now proved very serviceable. He passed the examination with great distinction, and in the course of it, to the surprise of the examiners, showed that he could repeat Euclid _verbatim_,--not by the exercise of the memory, which in Ericsson is not remarkably retentive, but from his perfect mastery of geometrical science. There is no doubt that it is this thorough knowledge of geometry to which he is indebted for his clear conceptions on all mechanical subjects. Having returned to the highlands, he entered on his new vocation with great assiduity; and, supported by an unusually strong constitution, he mapped a larger extent of territory than any other of the numerous surveyors employed on the work. There are yet in the archives of Sweden detailed maps of upwards of fifty square miles made by his hand.