Again, a horse canters best with off shoulder leading, if moving along the side of a hill which slopes up to his right, and _vice versa_. Thus, if you keep on the left side of most roads, where the grade slopes towards the gutter, you will find that Nelly will lead best with her right shoulder. This is for the same reason. She wishes to plant quickest that foot which will keep her from slipping down hill. If she is on the right of the road she will lead best with the left shoulder. She will, perhaps, not do this as readily as on the circle, but she will be apt to do it. If you should watch a horse in the circus ring, you would notice that this is apparently not true. But the slanting path of the circus ring is really not on a slant at all, when we calculate the centrifugal force of the motion around so small a circle. It is as if a horse were moving on a horizontal plane, for he is really perpendicular to the slanting path; and its tipped position is governed by the same mathematical rule as the road-bed of a railroad curve.
You may utilize this slanting instinct also in the same fashion as the circle first mentioned for getting the elementary idea into Nelly's head that pressure on one side means leading with the opposite shoulder. Moreover, the side of the road, which is the slope most handy, has the additional advantage of being generally the softest cantering ground.
There is an upward play of the rein, which can be explained only to the student who has advanced some distance in the art, which tends to lighten, or invigorate one or the other side of a horse, and thus induce him, coupled with other means, to make the long strides, that is, lead, with the lightened or active shoulder. But you, Tom, will not be able to use this until you have devoted more time to study as well as practice.
After you have tried the circle to your satisfaction, try cantering in a figure eight of sufficient size. Nelly will thereby learn instinctively to change step as she comes to the loops. You can probably find a field or lawn somewhere on which you can practice. Out-of-door instruction is always preferable to riding-school work, if equally good, both for man and beast. And such instruction as these hints are intended to enable you to give, will teach you more than the average riding-school ever does. I by no means refer to those schools which teach equitation as a true art, instead of merely drilling you in the bald elements of riding. Nor is there any better place to give Nelly proper instruction than a riding-school, unless it be the lawn or field. What you teach Nelly out-of-doors you will find her much more willing and able to put into use on the road than if she had gone through the same drill in a school.