As to the high-up saddle or centre of gravity, true, an inch side-slip at the ground, of a machine with a low-down centre of gravity, will cause it to assume a greater slant or angle from the vertical than a higher; hence our friend could well say that when the Safety starts to slip it will be more certain to go on down. It is to be noted, however, as against this idea, that other machines with low-down saddles do not slip. Taking all the theories and experiences, _pro_ and _con_, into consideration, I am inclined to believe that no one cause can account for the entire difficulty; it is probably a combination of smaller elements partly belonging to several of the theories advanced. The elements which have been most strongly urged are, first, the driver being small; second, the driver being in the rear; third, the weight being in the rear; fourth, the work being done between the wheels. All these seem to work to the same end. Again, any drive-wheel will slip worse than a non-driver, since a sliding force in any direction will tend to loosen the hold of the rubber tire from the surface of the road more than any rolling action. A short slide from a stone is felt more when the weight is upon the wheel, and the drop in rolling off so distinctly felt in connection with the small wheel is much sharper than a similar action of a large one. A rider can certainly manage himself better and more surely when he drives, steers, and leads with the same wheel and has his weight upon it. This is what he _does_ on the Ordinary and just what he _does not_ do on the rear-driver. The deepest and most profound explanation of all side-slip was recently proposed to the writer by a mathematician of great ability; but it is so complex that he has not worked it out himself yet, though expecting daily to hand in the solution. He says it is all from the relation of the points, first, of the centre of gravity, second, of the centre of oscillation, and third, of the transmission of power, to each other. Just where and how they ought to be is, as yet, not fully determined. To remedy the evil of the side-slip in the most obvious ways would be to make the rear-driving Safety no longer the same machine; it would ruin, to a great extent, the very qualities for which it is prized, and therefore, if any such theories as before enumerated should prove tenable, the only clear way out of the difficulty would be in the use of non-slipping tires, if such can be produced. In regard to the angle at which any machine will slip in rounding a corner, some, who have advanced the idea that the Safety slipped because it had to lean more, do not appear to be aware of, or take into account, the fact that the angle at which the cycle, or any other machine, must lean under such circumstances is entirely independent of the height of the centre of gravity. The angle is a function of the speed and radius of curvature only.