From the facts that have been stated above three or four conclusions may be drawn which perhaps may be considered to govern the question whether the expenditure was incurred in gaining or producing the assessable income. In the first place it seems indisputable that the increased knowledge the taxpayer sought and obtained of his subject and the closer and more realistic acquaintance he secured of modern developments in design and construction made his advancement in the service more certain, and that in respect of promotion to a higher grade these things might prove decisive. This was put clearly by the Principal Architect, though in a letter written ex post facto, "I understand from you that the Commissioner now desires to know whether the experience obtained and the large amount of data collected will result in an increase in your income. To me, it is obvious that this must increase your professional efficiency, and hence your value to this Department, and must materially assist your future advancement to a higher position in the Department with consequent increase in income." In the second place, so far as motive or purpose is material, advancement in grade and salary formed a real and substantial element in the combination of motives which led to his going abroad. In the third place it is apparent that the heads of his Department, and indeed the Government itself, treated the use which he made of his long service and other leave to study architecture, increase his professional knowledge and study modern trends, as a matter not only of distinct advantage to his work for the State but of real importance in at least one project in hand. In the fourth place it was all done while he was in the employment of the Government, earning his salary and acting in accordance with the conditions of his service. He was in fact complying with the desires, and so far as going to South America was concerned, with the actual request of the Government. His journey abroad and what he did while in Europe, as well as in South America in the following year of income, was therefore in a correct sense incidental to his employment and most relevant to it.