This procedure, adopted in the preparation and judgment of each new piece of evidence, excludes error as far as our means conceivably permit. Only one thing more is needful--a narrow and minute research into that order of succession which is of indispensable importance in every natural science. ``Of all truths concerning natural phenomena, those which deal with the order of succession are for us the most important. Upon a knowledge of them is grounded every intelligent anticipation of the future'' (J. S. Mill). The oversight of this doctrine is the largest cause of our failures. We must, in the determination of evidence, cleave to it. Whenever the question of influence upon the ``_*effect_'' is raised, the problem of order is found invariably the most important. Mistakes and impossibilities are in the main discovered only when the examination of the order of succession has been undertaken.
In short: We have confined ourselves long enough to the mere study of our legal canons. We now set out upon an exact consideration of their material. To do this, obviously demands a retreat to the starting-point and a beginning we ought to have made long ago; but natural sciences, on which we model ourselves, have had to do the identical thing and are now at it openly and honestly. Ancient medicine looked first of all for the universal panacea and boiled theriac; contemporary medicine dissects, uses the microscope, and experiments, recognizes no panacea, accepts barely a few specifics. Modern medicine has seen the mistake. But we lawyers boil our theriac even nowadays and regard the most important study, the study of reality, with arrogance.
 J. S. Mill: System of Logic.
Topic II. PSYCHOLOGIC LESSONS.
Section 3. (a) General Considerations.
Of the criminalist's tasks, the most important are those involving his dealings with the other men who determine his work, with witnesses, accused, jurymen, colleagues, etc. These are the most pregnant of consequences. In every case his success depends on his skill, his tact, his knowledge of human nature, his patience, and his propriety of manner. Anybody who takes the trouble, may note speedily the great differences in efficiency between those who do and those who do not possess such qualities. That they are important to witnesses and accused is undoubted. But this importance is manifest to still others. The intercourse between various examining judges and experts is a matter of daily observation. One judge puts the question according to law and expects to be respected. He does not make explicit how perfectly indifferent the whole affair is to him, but experts have sufficient opportunity to take note of that fact. The other narrates the case, explains to the experts its various particular possibilities, finds out whether and what further elucidation they demand, perhaps inquires into the intended manner and method of the expert solution of the problem, informs himself of the case by their means, and manifests especial interest in the difficult and far too much neglected work of the experts. It may be said that the latter will do their work in the one case as in the other, with the same result. This would be true if, unfortunately, experts were not also endowed with the same imperfections as other mortals, and are thus far also infected by interest or indifference. Just imagine that besides the examining magistrate of a great superior court, every justice and, in addition, all the chiefs and officials manifested equal indifference! Then even the most devoted experts would grow cool and do only what they absolutely had to. But if all the members of the same court are actuated by the same keen interest and comport themselves as described, how different the affair becomes! It would be impossible that even the indifferent, and perhaps least industrious experts, should not be carried out of themselves by the general interest, should not finally realize the importance of their position, and do their utmost.
The same thing is true of the president, the jurymen and their fellow-judges. It is observable that here and there a presiding justice succeeds in boring all concerned during even criminal cases interesting
in themselves; the incident drags on, and people are interested only in finally seeing the end of the matter. Other presiding justices again, fortunately the majority, understand how to impart apparent importance to even the simplest case. Whatever office anybody may hold,--he and his mates are commissioned in the common task, and should the thing come up for judgment, everybody does his best. The difference here is not due to temperamental freshness or tediousness; the result depends only upon a correct or incorrect psychological handling of the participants. The latter must in every single case be led and trained anew to interest, conscientiousness and co-operation. In this need lies the educational opportunity of the criminal judge. Whether it arises with regard to the accused, the witness, the associate justice, or the expert, is all one; it is invariably the same.
That knowledge of human nature is for this purpose most important to the criminalist will be as little challenged as the circumstance that such knowledge can not be acquired from books. Curiously enough, there are not a few on the subject, but I suspect that whoever studies or memorizes them, (such books as Pockel's, Herz's, Meister's, Engel's, Jassoix's, and others, enumerated by Volkmar) will have gained little that is of use. A knowledge of human nature is acquired only (barring of course a certain talent thereto) by persevering observation, comparison, summarization, and further comparison. So acquired, it sets its possessor to the fore, and makes him independent of a mass of information with which the others have to repair their ignorance of mankind. This is to be observed in countless cases in our profession. Whoever has had to deal with certain sorts of swindlers, lying horsetraders, antiquarians, prestidigitators, soon comes to the remarkable conclusion, that of this class, exactly those who flourish most in their profession and really get rich understand their trade the least. The horsedealer is no connoisseur whatever in horses, the antiquarian can not judge the value nor the age and excellence of antiquities, the cardsharp knows a few stupid tricks with which, one might think, he ought to be able to deceive only the most innocent persons. Nevertheless they all have comfortable incomes, and merely because they know their fellows and have practiced this knowledge with repeatedly fresh applications.