This is part two of this article. To read the first part, please click here.
In evaluating books therefore, we must take three things into account.

The first thing you must consider is yourself. The value of a book to you is the value that you, with your experience and background knowledge can gain from that book, not what someone else, with an entirely different preparation, would stand to gain. Not all mines are workable with the same equipment. A prior consideration of the “equipment” you are bringing to the task is essential to an accurate assessment of the points that follow. A book that would be illuminating to someone with prior knowledge of a subject might only confuse someone who has none.
The second thing you must consider is how much “gold” the book contains. Almost all books, even the most worthless contain something of benefit, however minuscule that benefit may be. Yet a flake of gold leaf does not prove a mine worthwhile—and a good point here and there goes no further for a book. If a book is to be worth reading, there must be something in it that is valuable enough to justify the time you are putting forth, to say nothing of what follows.
The third thing you must consider is the danger the book poses to you. Mines are often dangerous and so are books. Both are worth entering but both require caution. The gold in a mine is of no value if you die before you can bring it to the surface. It is crucial to remember is that books are not dangerous to you simply because you disagree with them. Books are most dangerous, not when they are obviously wrong, but when they are subtly misleading in ways that you do not have the preparation to detect or resist.

It is only by the simultaneous consideration of each of these three areas that books can safely be judged. Taking only one of the three considerations above into account is not enough. In prospecting, a mine can only be adjudged worthwhile if the workability, profitability, and liability of working its shafts each receive adequate consideration. The same is true of books. The benefit of well chosen reading is immense—the danger of careless selection is equally great. Prospect carefully.