One advantage cannot be denied of this now popular and established method of setting forth scientific truth, viz., that it prescribes a convenient method of bringing into contrast the arguments _for_ and _against_ any disputed position in science. If materialism can furnish its ready advocate with a convenient vehicle for its ready diffusion, the antagonist theory can avail itself of a similar vehicle for the communication of the decisive and pungent reply. The one is certain to call forth the other, and if the two are present side by side in the same series, so much the better is it for the truth and so much the worse for the error. The teacher before his class, the lecturer in the presence of his audience, has the argument usually to himself; he allows few questionings and admits no reply. An erroneous theory may entrench itself within a folio against arguments which would annihilate its positions if these were condensed in a tract. This consideration should dispel all the alarm that is felt by the defenders of religion in view of the general diffusion of popular scientific treatises. The brief statement of a false or groundless scientific theory, even by its defender, is often its most effectual refutation. A magnificently imposing argument often shrinks into insignificance when its advocate is forced to state its substance in a compact and close-jointed outline. The articulations are seen to be defective, the joints do not fit one another, the coherence is conspicuously wanting. Let then error do its utmost in the field of science. Its deficient data and its illogical processes are certain to be exposed, sometimes even by its own advocates. If this does not happen the defender of that scientific truth which seems to be essential to the teachings and faiths of religion, must scrutinize its reasonings by the rules and methods of scientific inquiry. If science seems to be hostile to religion, this very seeming should arouse the defender of Theism and Christianity to examine into the grounds both by the light and methods which are appropriate to science itself. The more brief and compact and popular is the argument which he is to refute, the more feasible is the task of exposure and reply. Only let this be a cardinal maxim with the defender of the truth, that whatever is scientifically defended and maintained must be scientifically refuted and overthrown. The great Master of our faith never uttered a more comprehensive or a grander maxim than the memorable words, “_To this end was I born and for this cause came I into the world, that I should bear witness unto the truth. Everyone that is of the truth heareth my voice._” It would be easy to show that the belief in moral and religious truth and the freedom in searching for and defending it which was inspired by these words have been most efficient in training the human mind to that faith in the results of scientific investigation which characterize the modern scientist.