These two careful and elaborate studies of the problem of disarmament have attracted wide attention among its students in Europe and the United States. Both have appeared in the year in which probably more definite thought than ever before has been given to the subject by men earnestly striving to find the entrance to some path that may lead to the solution. These volumes plainly show that the writers—than whom no one can have thought more deeply—are convinced that it is not a problem for abstract reasoning. It is not like an equation in mathematics where the application of definite rules leads to one exact conclusion. In such a problem, if there are unknown factors, they are inert things; they are subjected, without evoking protest, to any sort of torturing process of analytical reasoning to determine their value, and that being done the problem is solved. But in this other problem the factors are living, sentient things; human beings acting of themselves in the mass or under the influence of individuals; swayed by every sentiment of the mind, fear, suspicion, greed, ambition, and by the highest and purest as well; sentiments perhaps dormant at one time, at another in intense activity, sometimes thinking and reasoning and again appearing as a wild outburst of senseless passion, and at all times subject to direction towards purposes good or ill according to the character of some guiding mind. No wonder that so many think it a waste of time to study the problem at all while, at the best, it seems to be one the solution of which can be arrived at only by a long slow process of empiricism.