It is most important also to be certain that the joint between the carbide holder and the lamp body is perfect, otherwise gas escapes, making a smell, also causing the pressure to the burner to be reduced, and may catch light from the burner and cause damage to the lamp. Electric lamps may be run off either a dry battery or an accumulator, or off a small dynamo driving off the machine tyre or wheel rim. In the case of running the lamp off a battery or accumulator, care is required to see that these together with the lamp, wires and switch are in good order. If the light fails suddenly, see first that the switch has not opened, or the wires dropt off the battery, etc., change the lamp or bulb for one known to be in good order; if there is still no light examine, and if necessary change the wires ; a sudden failure of the light is nearly certain to be due to one of these troubles. A gradual failure of the light is probably due to decrease of voltage of the battery, etc. These will mean new dry batteries, and a recharge of the accumulator if such is used. If the light is run off a dynamo, then a sudden failure might now include such points (in addition to the above) as failure of contact between the dynamo pulley and the tyre or rim, or a short circuit in the dynamo itself; in this latter case the dynamo will almost certainly get very hot and may smoke ; this will probably mean its return to the makers. It may, however, only be due to a failure connected with the dynamo brushes on the commutator; a brief examination will reveal such a fault. In all such tests carried out to discover a fault be careful to carry out only one alteration, etc., at a time, and note result, and refer to pages on Testing, also on Dynamo. The cranks are now generally fastened to the crank axle by means of cotters, and should it be required to take such out, loosen the nut, take it off and tap the cotter screwed end with a hammer, taking care to hold a piece of lead or copper over the screwed end to avoid damage, also hold a heavy block under the crank boss so that no shock comes on to the ballbearings in the crank bracket. If the two cranks do not stand quite in line with one another, try the effect of reversing one of the cotters, if this does not put them in correct line, then the flat cotter face must be filed to correct the fault. If a crank has become loose on the axle, then generally tapping the cotter in further will tighten it, but it may be that continued use in a loose condition has damaged the cotter face so much that it must be filed up to a true flat once more. In the event of a fall the most frequently damaged part appears to be the pedal pin, which gets bent. In such a case the best thing to do is to take off the bearing cap on the outside pedal ball-bearing, take off the adjusting cone, take out the balls, then move the pedal frame along the pedal pin and catch the balls from the inside pedal bearing. This leaves the pedal pin only attached to the crank, and visual inspection will show where the pedal pin is bent; it should then be taken off and heated to a black heat at the bend, and by means of a lead hammer and an anvil or suitable block be straightened. If no block is available, it may be properly held in a heavy vice. Should the crank itself be bent, the same type of treatment must be followed, but no attempt at any straightening must be done while the bent part is attached to the cycle, otherwise further damage is likely. To replace the balls in the pedal case use some thick grease in the ball cups, and bury the balls in this, they will then remain in position while the pedal pin is inserted, and the adjusting cone tightened up. Pedal pins are now generally screwed into the crank ends, and to prevent them coming out while pedalling they are generally screwed right-hand for one side, and left-hand for the other side, so that care is required in unscrewing, i.e., a left-hand thread being on the right-hand pedal. The pedals should be screwed into the cranks firmly, but without undue force. In the use of all spanners on a cycle, care should be taken that the spanner does fit the nut properly; nothing spoils the look of a cycle (as regards mechanic-a] details) sooner than nuts with the corners rubbed off, and nothing makes future adjustments more difficult and irritating than a damaged nut that no spanner will hold. The modern cycle saddle is generally provided with means of altering the tension on the leather, so that the leather can be tightened up when required. This is frequently by means of a nut or a bolt underneath the saddle peak. Cycle bells may be of single or double sounding dome shaped bells; generally the mechanism consists of a finger trigger, pulled one way by the rider, and returned by a spring, this trigger operates a toothed curved quadrant engaging with a toothed wheel, on this wheel is mounted two arms, at the ends of which small weights are free to slide outwards when the arms are turned rapidly by the wheel. These weights strike a projection on the inside of the bell or gong making it sound at every stroke. In the event of the bell not sounding when the trigger is operated, or the trigger refusing to move, the gong should be turned in a counter-clock direction, inspection of the interior will show the trouble. This is generally due to want of a little oil, or the trigger or bell main axle may be bent, due to a fall, etc., or the returning spring may be broken; probably a temporary repair may be made by a pair of pliers, bending one of the broken spring ends to engage in the hole provided for it. The cycle driving chain should be kept as clean as possible, well oiled, and at the correct tension. Wear on the chain takes place of course at the joints, and the pitch of the chain (i.e., distance between adjacent rivets or joints) will increase as it wears. This will in time cause trouble since the pitch of the chain wheels will remain constant. A sure test for this trouble is to inspect the chain as it lies on the large chain wheel, and try and lift it away from the chain wheel in the centre of its arc of contact. If it can only be lifted say 1/8 inch, it is in good order, but a lift of 1/2 inch means that there is a risk that the chain will sooner or later ride up upon the teeth, and either be thrown off or broken. The remedy for such a chain is to replace it with a new one. An easy running machine is one in which all the bearings, also the driving chain, are properly adjusted and oiled, and a dust-proof gear-case, preferably with an oil bath, is well worth the extra cost and weight.