SCIENTIFIC NOTES.

Press, Volume LI, Issue 8708, 2 February 1894, Page 3

SCIENTIFIC NOTES.

Scientific _imerica_.

It can be taken as a fact, which tha theory of Lhe action of the eye implies, that for each external impression, that Is, for each image produced on the retina, the ends of the visual nerves concerned In the conveyance of the impression to the mind must be under a peculiar stress or In a vibratory state. It now does not seem improbable tbat. when by the -power of thought an [range is evoked, a distant reflex action, no matter how weak, is exerted upon certain ends of the visual nerves, and, therefore, upon tlie retina. Will it ever be within lmm.n power to analyse the condition of the retina when' disturbed by thought or reflex action, by the help of some optical or other means of such sensitiveness that a clear Idea of its state might be gained at any time? If this were possible, then the problem of reading oue'. thoughts witb precision, like the characters of an open book, might be much easier to solve than many problems belonging to the domain of positive physical science, in the solution of which many, if not the majority, of scientific men Implicitly believe. Helmholtz has shown that the fundi of the eyes are themselves luminous, and he was able to see, in total darkness, the movement of his arm by the light of his own eyes. This is one ot the most remarkable experiments recorded in tbe history of science, and probably only a few men could satisfactorily repeat It, for It Is very likely that the luminosity of the eyes Is associated with uncommon activity of the brain and great, imaginative power It is fluorescence of brain action, aa lb were.

Few bicyclists are probably aware of the fact that they.have been .the means of bringing about a new departure in machine - construction, and of establishing an important manufacturing industry quite apart from that of the cycle itself. The use of ball bearings to reduce friction is an old device, but the attainment of anything like ideal results is a matter of great difficulty. The best anti-friction bearing ia one in which the balls are so interposed between the bearing surfaces that the only friction existing is that caused by the point of contact of euch ball with its neighbour. In order to attain this result the balls mußt be absolutely of one sise, they must be quite spherical, and the material of which they are made must have the physical properties necessary to stand the excessive wear and tear. We condense the following account of the manufacture of the balls from a recent number of Engineering : — The wire or rod from which the balls are made is ot the best crucible cast Bteel of the closest grain, and costs about .MO per ton. This rod is a little larger tn diameter than the size of the balls, varying from JMnch up to _ inches, and is fed by self-acting machinery through the hollow mandril of a lathe up to a series of cutters. The first thing done Is to turn a neck in the Wire ; when this is finished the wire la fed 00, and by the second cutting the neck is made into two half circles, At the next stage the roughly .turned.ball, not quite separated from its neighbour, is brought under a rotating crown cutter, which produces a sphere, while the final cutter ueparate. the balls from the wlr. one by one. This machine turns out the balls true to the one three-hundredth of the finished; size. It is automatic in its action, the Wire ortly requiring to be placed in, when a hew length is used, and when the length I. used up th. machine throws Itself out of gear. The balls are next taken j to the lapping department, where they are ground to au accuracy ot one two-thou--1 sand th of an inch. This operation Is carried out by grinding them with powdered [ emery and oil in grooves on the faces ot tha i cast Iron laps. The grooves must be kept, accurately to size, and are being constantly turned down as they become wOrn. Each grove is not a complete half circle, but is a curve, the radius of which is slightly mora than half the diameter ot the finished ball. After tho balls have been ground in this way they are tempered, an operation requiring the greatest care so that all the balls may be of the same degree Of hardness. They are heated over ag_."furnace, and it has been found best, in order to get the right temperature, to trust to the skilled eye of the operator, the hardening room being always kept in a uniform state of illumination. When they are heated to the right colour, they are thrown into a large tank 6t water. After this they aro ground again, and finally polished between rapidly revolving wooden laps. The balls are now exact spheres and of uniform hardness, hub they have to be tested as to size. They are allowed to roll along, two bars ot hardened steel, which are placed at a given distance aparr. The drat machine allows all the balls which are too large by the one two-thousandth ot an Inch to pass, on, while those of correct size or smaller fall , through. A second similar machine, but - with the bars half a thousandth of an inch closer together, picks out any that are too small by the same amount. The operation may be divided ap Into several stoges. so as to get a gradual and more accurst*. [sifting, but tbe usual limit Of error g.ven is that above stated. I. Is of the first Importance that all the balls in a bearing should be of one size, and If one be a thousandth of an inch larger fcbati its follows, it not only sustains all the weight, but also has to push all the remaining balls of the set round. The Aufce Machinery Company of Coventry turns ou. about 80,000 balls a day, mostly of the smaller aizts, but the larger ones are fast coming into requisition. They are used not only for bicycles and similar machines but also for carriage axles, engines, lathes, | dynamos and many other kinds of machinery.'