This section is from the book "Horses, Guns, And Dogs", by J. Otho Paget, George A. B. Dewar A. B. Portman, And A. Innes Shand. Also available from Amazon: Horses, guns and dogs.
The bridle is a most important instrument to a horseman, and it therefore deserves rather more attention than we have hitherto devoted to it. In conjunction with a pressure of the legs, the bridle is the medium which conveys our wishes to the horse.
Some perhaps may imagine it possible to stop a horse by the mere strength of arm, but if they will only give the matter a moment's thought, they will see that when seated on a moving object you have no power to arrest its progress. You could just as easily expect to stop a boat in which you were a passenger by hauling on the painter. I am not sufficiently learned in the subject to describe my meaning in the proper scientific language, but we must all of us have enough sense to know that, to exert any power of leverage, a fulcrum is necessary. When on the back of a horse, the only medium by which we can establish a fulcrum with the earth is through our body to the animal's hind feet. This power is, however, very small, but for that reason we must make the most of it and use it to the best advantage.
Now we cannot expect a horse to walk about on his hind legs, and each of his fore feet must in turn touch the ground eventually if he is to make any progress. You will therefore say, how is that leverage to be obtained ? To get the leverage you will depend entirely on balance, and this is the whole secret of a feeble man being able to control such a powerful animal. You must so manipulate the bridle that the balance of your body comes on the horse's hind quarters, but directly that weight is shifted to the fore-hand, your power is gone and you are practically a helpless passenger. This is my theory, and I may very likely be wrong, but I do not want you to accept what I have stated as gospel without first reasoning it out for yourself. I venture to think you will agree with me, and we will proceed on that assumption.
The curb bridle is of course the means by which you get the most power over a horse, but it is an instrument that requires very delicate handling, only to be used by horsemen of experience and possessing that lightness of touch which we call " hands." In referring here to the curb, I mean that bit and the snaffle-iron combined, but we will first of all discuss the merits and disadvantages of the latter.
The plain snaffle is the father and origin of all other bits. When used in conjunction with a martingale, it can be made to answer the purposes of the double-reined curb, but the snaffle should then have two reins attached. I have already explained that the bit should lie on the bars of the horse's mouth, and that when it works up to the corners it becomes useless as a bridle. The" martingale prevents the horse from throwing up his head, and thus the bit falls into the right position. You must, however, remember that throwing up the head is the only method the animal has of protesting against the unmerited pain which his rider inflicts.
No boy or man who is not an accomplished rider should ever be allowed either a martingale or curb. The former is an instrument of considerable use in controlling a young horse in the hands of a good horseman, but I would never advise a beginner to risk anything that is not perfectly trained.
When I began to ride regularly the first bit of horseflesh I owned was a game little mare with an extraordinarily light mouth, and fortunately for me her late owner advised that she should never have anything except a plain snaffle. In those days I had confidence in the strength of my muscle, and did not appreciate the importance of delicate handling. The consequence of this was, if I wanted to stop I took a dead pull at the reins, when up the mare's head would go, with her ears in my face, and the bit in the corners of her mouth. In that position I could pull until I was tired out, but it never inconvenienced the mare or arrested her onward progress. Gradually it dawned upon me that physical force was of no avail, and I got into the habit of treating her mouth as a thing to be touched very tenderly.
You will understand that if I had tied her down with a martingale she could never have taught me that practical lesson, and it is for that reason I have introduced this personal incident.
Although less harm can be done to a horse's mouth with a snaffle by hanging on to the bridle than would be the case with a sharper bit, you must still use it with all gentleness. The plain snaffle is a very valuable bit when properly handled, and a horse will bend to it as easily as to a curb, but you must play with it in his mouth, and never take a steady pull.
Try to forget that you have any strength in your muscles, for if you were a Hercules your strength would all be wasted in hauling on the bridle. The system which you should always go upon is that of "give-and-take." "Do not pull at a horse and he will not pull at you " is advice that has been written and spoken by many instructors on riding, but it is such a valuable rule to remember that I must be excused for repeating it here.
A confirmed runaway is of course not pleasant to ride on with only a snaffle, but I do not advise any inexperienced horseman to mount an animal of such character. A horse with an excellent reputation may, however, in a momentary exuberance of spirits and with a feeling of contempt for a snaffle, suddenly take it into his head to go faster than you think desirable. Unless you can bring him under control again, the pace is liable to increase, and in a few more seconds you will find yourself run away with. The beginner's first and only idea is to haul at the reins with all his might, but however muscular he may be his strength soon gives out, and he then becomes a helpless passenger.
The horse that goes off with his head up in the air, and has no martingale to bring it down, is generally the easiest class of runaway to deal with, though, as he cannot see where he is going, his rider is in a very uncomfortable position for a few seconds. All you have to do is to shake the reins and drop your hands on the withers, when the horse will soon lower his head, and you can get a gentle feel of his mouth again.
 
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