760 . REPORT — 1894. 



5. On Lighthouse Apparatus and Lighthouse Administration in 1894. 

 By J. Kenwaed, F.S.A., Lighthouse Engineer. 



The writer referred to the principles that govern the establishment of modern 

 lights, and described the chief forms of apparatus now best available for the optical 

 engineer, e.g., the single Hashing or the group-flashing holophotal revolving ; the 

 fixed and occulting ; the lenticular revolving, having refracting centres alone, 

 extended to high vertical angles ; and the quick-flashing lights of recent French 

 types caWe-A feux-eclairs. 



He compared the dimensions or ' orders ' of various apparatus, and the radiants 

 of gas, oil, and electricity, and discussed the question oifog in relation to these. 



He called attention to the need of good ship-lights on the dioptric system, 

 having equality of power in the beam. 



He suggested certain reforms in lighthouse administration and in lighthouse 

 statistics. 



6. On Spring Spokes for Bicycles. By Professor J. D. Everett, F.R.S. 



The author described a construction of spring-spoked wheels for bicycles in 

 •which both lateral and rotational yielding are so moderate in amount as to 

 occasion no inconvenience. Each spoke consists essentially of a small coil spring, 

 weighing half an ounce, attached to a light spoke wire, the connections of the ends 

 of the spoke to hub and rim, as well as the connection between spring and wire, 

 being of the hook-and-eye kind. The attachment to the rim is made, not at the 

 centre of the rim, but at its edges, semicircular notches being cut, into which the 

 spokes are hooked, and the spokes attached to either edge of the rim are attached 

 to the opposite flange of the hub, so as to cross the plane of the wheel. The 

 spokes of the driving-wheel are not exactly radial, but slope a little backwards 

 and forwards alternately — an arrangement which materially diminishes rotational 

 yielding, while the crossing above described diminishes lateral yielding. 



It has generally been maintained that, while up-and-down elasticity is useful 

 for relieving jolts, lateral and rotational yielding are evils to be avoided. The 

 author differs from this view, and maintains that both lateral and rotational 

 yielding, of the elastic kind, when kept within proper limits of magnitude, are 

 beneficial both as regards comfort and speed. 



When one of the wheels of a bicycle encounters an obstacle (such as rough 

 roads abound with), the collision produces an impulsive reaction on the wheel, aa 

 if the obstacle struck the wheel. Sometimes the direction of the blow lies in the 

 plane of the wheel, but in many cases the wheel is not only checked and lifted, but 

 at the same time driven to one side. In order to cushion the lateral component of 

 the blow there must be lateral yielding. Accordingly, in running over patches of 

 stones, which jerk the ground-point of a wheel from side to side, the usual jarring 

 of the hands and disturbance of the steering are noticeably absent in bicycles with 

 spring spokes. 



As regards a blow delivered in the plane of the wheel, the impulse may be 

 resolved into a radial and a tangential component. The radial component is 

 cushioned by the shortening of the spokes in the neighbourhood of the point of 

 impact, and the lengthening of the diametrically opposite spokes. 



The tangential component is equivalent to an equal and parallel impulse on the 

 rim in a line passing through the centre, combined with a torque. The torque, 

 from the symmetry of its action round the axle of the wheel, produces no jar ; but 

 the impulse in a line through the centre tends to drive the rim backwards and 

 slightly downwards, with respect to the axle. It is cushioned by the elastic 

 shortening and lengthening of spokes which are nearly horizontal. 



The elastic yielding of a pneumatic tyre is mainly in the radial direction, and 

 is practically nil in the tangential direction. Its lateral yielding is very much less 

 than that aflbrded by spring spokes. 



Next, as regards rotational yielding of the driving-wheel, the propelling force 



