Fixing the Attention

What is commonly called abstracted  (concentration) thought whilst studying  is nothing more than having the attention so completely occupied with the subject in hand, that the mind takes notice of nothing outside of  itself. 

One of the greatest minds which this or any other country ever produced, has been known to be so engrossed in thinking on a particular subject, that his horse had waded through the corner of a pond; yet, though the water covered the saddle, he was wholly insensible to the cause of his being wet and so noticed not a thing.

I mention this, not to recommend such an concentration, but to show that he who has his attention fixed, as well as the power of fixing it when he pleases, will be successful in whatever study he chooses. 
Why does the boy who has a large sum upon his slate, scowl, and rub out, and begin again, and grow discouraged ? Because he has not learned to govern his attention. He was going on well, when some new thought floated into his mind, or some new object caught his eye, and he lost the train of calculation which resulted in the wrong sum.
Why has the Latin or Greek word so puzzled you to remember, that you had to look it out in your dictionary ten or a dozen times? 
And why do you look at it as at a stranger, whose name you ought to know, but which you cannot recall ? Because you have not yet acquired fully the power of fixing your attention when he first said it. For had you, that word would have been remembered long since, if it had not passed as a shadow before your mind, seen but not remembered.
A celebrated authoress, who states that she reserves all her i’s to be dotted, and her t’s to be crossed on some sick day, might have given a more philosophical reason; and that is that she could not bear to have her attention interrupted a single moment, when writing was at it most success. — The Student’s Manual
from the California Farmer, 1855