THREE:The following are suggested as subjects which may be studied in connection with lathes and turning: the rate of cutting movement on iron, steel, and brass; the relative speed of the belt cones, whether the changes are by a true ascending scale from the slowest; the rate of feed at different changes estimated like the threads of a screw at so many cuts per inch; the proportions of cone or step pulleys to insure a uniform belt tension, the theory of the following rest as employed in turning flexible pieces, the difference between having three or four bearing points for centre or following rests; the best means of testing the truth of a lathe. All these matters and many more are subjects not only of interest but of use in learning lathe manipulation, and their study will lead to a logical method of dealing with problems which will continually arise.If Plotinus rose above the vulgar superstitions of the West, while, at the same time, using their language for the easier expression of his philosophical ideas, there was one more refined superstition of mixed Greek and Oriental origin which he denounced with the most uncompromising vigour. This was Gnosticism, as taught by Valentinus and his school. Towards the close of our last chapter, we gave some account of the theory in question. It was principally as enemies of the world and maligners of its perfection that the Gnostics made themselves offensive to the founder of Neo-Platonism. To him, the antithesis of good and evil was represented, not by the opposition of spirit and Nature, but by the opposition between his ideal principle through all degrees of its perfection, and unformed Matter. Like Plato, he looked on the348 existing world as a consummate work of art, an embodiment of the archetypal Ideas, a visible presentation of reason. But in the course of his attack on the Gnostics,518 other points of great interest are raised, showing how profoundly his philosophy differed from theirs, how entirely he takes his stand on the fixed principles of Hellenic thought. Thus he particularly reproaches his opponents for their systematic disparagement of Plato, to whom, after all, they owe whatever is true and valuable in their metaphysics.519 He ridicules their belief in demoniacal possession, with its wholly gratuitous and clumsy employment of supernatural agencies to account for what can be sufficiently explained by the operation of natural causes.520 And, more than anything else, he severely censures their detachment of religion from morality. On this last point, some of his remarks are so striking and pertinent that they deserve to be quoted.
