Page:Popular Science Monthly Volume 49.djvu/780

756 in borrasca, and they may never again pay a profit to their owners. Still, with faith and endurance that are sublime, the heroes of the Comstock cling to its fallen fortunes, and continue the search for new bonanzas.

[—The full story of the mines, as illustrated by the great Comstock lode, prepared by Mr. Shinn, will constitute the next volume of the Story of the West Series, edited by Mr. Ripley Hitchcock, to be published by D. Appleton & Co. in October. Our readers need hardly be told that Mr Shinn has special qualifications in his familiar acquaintance with the subject and his rare literary skill, which will impart special interest and value to this work.]



E are able to calculate almost precisely the amount of work any given machine—as a steam engine or an electric-lighting plant—is capable of performing, and the amount of fuel that will be required to develop the calculated power. When we come to man we are much less certain, although a skillful army surgeon can tell almost at a glance whether the recruit standing before him is strong enough to meet the requirements of the service, and there are machines in the market that will inform us in what time we can pull a given weight to a given height. But we have no measure that we can apply to the capacity for mental work, and no units of mental valuation. The most we can do is to compare the intellectual capacity of one man with that of another by the mental results they have severally achieved in practice. When we wish to test the fitness of a candidate for a position of trust or responsibility, we subject him to an examination, which relates, however, mostly to what he has learned, and from which we guess in a rather indirect way what he may be capable of doing in the future, and with relation to other matters than those on which we examine him; and the test is very often deceptive: for those who have made the most brilliant displays in the examination frequently fail in capacity to make practical application of what they have learned only theoretically; or they fail by irregularity, frequent and marked changes in their disposition to work, want of endurance, or too great dependence on external conditions, of which the examination gives no prediction. Such efforts as have been made to obviate this difficulty have hitherto failed to meet their object.

It has, however, recently become possible to reach fairly approximate conclusions concerning mental capacity, such as 