No doubt the old Kangaroo, as bad a failure as it was, led us up to endure more complacently the rear-driver in respect to the sprocket-chain; yet in no type of machine could the subject have been brought to our notice in a worse form. The tricycles using a single chain did away with one of the great evils which appertain to this system as found in the Kangaroo, in which we have two chains working entirely independently. The evil of such an arrangement is easily seen: no old Kangaroo rider, or rider of any other double-chain device, is ignorant of the annoyance caused by reversing the slack in each at every half-revolution of the pedal. Keep the chains ever so tight, this slack will be felt as the pedal crosses the dead-centre line at the top and the bottom. In spite of all this, some reputable makers persist in constructing rear-drivers having the double chain, and as a matter of course justly fail to meet with much approval from the riders thereof. A word in regard to the nature of sprocket-wheels and chain. It is perhaps not generally understood how important it is that they should be well made, with especial view to resist stretching and alteration of pitch, any tightening device, no matter how deftly made, being an inconsistency in mechanics. To be sure, the spreading of the wheel-centres cannot do much harm, and it saves some annoyance, but it does not cure the real evil, nor is it any better to take a link out; it is the length of each and every link that is wrong, and it can only be cured by either changing each link or by altering the sizes of the sprocket wheels.