Perhaps some of you may feel that there are many other problems to be encountered before you will meet these which I have set forth.  But we should remember that the mind holds some of such impressions a very long time.  It holds them below the threshold of conscious thought, and under ideal working conditions it brings them above it when they are needed.

If you have caught my meaning you will not be weakened in enthusiasm for new work, but you will be protected in a measure against some of the reaction due to disappointment.  There is a great field for earnest workers, and it is easy to become one by working on the lines set forth.

Natural Fitness.

One of the first questions that arises in the mind of one who intends to undertake machine design is, what constitutes natural fitness for it.  There seems to be no positive basis on which to determine in advance a natural fitness for this work, but there are certain temperamental characteristics that undoubtedly have much to do with the success.

The temperament should be one favorable to continuity of thought along a given line, as well as one that will by nature take an intense interest in the subject.

If these characteristics are missing, it may be due more to the distracting interests that in these days crowd in upon the mind, than to a lack of natural aptitude.  The absorbing interest, however, is essential, and it may be developed by conforming to well-known principles of orthodox psychology.  Self-torture or hard driving is not nearly as helpful as a strong inner purpose to keep the chosen subject in the real center of conscious thought.

The subject that comes to mind when there is a lull in the outside demands on the attention, or one that is insistent on taking possession of the mind, even when other matters are objectively more in evidence,—­that subject is the one that holds the center of the inner attention.  That is the controlling idea or purpose.  Ordinarily, it is some diversion; occasionally, the haunting bugbear of some unfinished work or obligation.  If the mind is dominated by such ideas or any other than the real problem in hand, the individual is seriously handicapped.

When a problem of machine design is undertaken, the mind must make it the real center of attraction.  To one having an average endowment for such work, this is not a difficult task, but to get the best results it should be rightly undertaken.

Repeated Thinking.

A chosen subject is brought, with some lasting effect, to the center of attention by repeatedly bringing it into the mind at the moments of lull in the pressure of other affairs.  The astronomers wait for the moment of best seeing, and the designer must wait for the actual psychological moment.

The best seeing condition for the astronomer is due in a small measure to his own physical condition, and in a large measure to atmospheric conditions, but the most opportune time for clear-headed vision of the designer is due mostly to his own physical and mental condition.