of velocity; and that moreover the very constituent parts of foreign Horses differ as much from all others, as their performances.  But this, however, will be found a truth; that in all Horses of every kind, whether designed to draw or ride, this principle of proportion will determine the principle of goodness; at least to that part of it which we call bottom.  On the other hand, our daily observation will shew us, that no weak, loose, disproportioned Horse, let his blood be what it will, ever yet was a prime racer.  If it be objected, that many a plain ugly Horse has been a good racer; I answer that all goodness is comparative; and that such Horses who have been winners of plates about the country, may be improperly called good racers, when compared to some others:  but I can even allow a very plain Horse to be a prime racer, without giving up the least part of this system:  for instance if we suppose a Horse (with a large head and long ears, like the Godolphin Arabian) a low mean forehand, slat sided, and goose rumped, this, I guess, will be allowed a plain ugly Horse; but yet if such a Horse be strong, and justly made in those parts which are immediately conducive to action; if his shoulders incline well backwards, his legs and joints in proportion, his carcase strong and deep, his thighs well let down, we shall find he may be a very good racer, even when tried by the principles of mechanics, without appealing to his blood for any part of his goodness.  We are taught by this doctrine of mechanics, that the power applied to any body, must be adequate to the weight of that body, otherwise, such power will be deficient for the action we require; and there is no man but knows a cable or chord of three inches diameter is not equal in strength to a chord of four inches diameter.  So that if it should be asked why a handsome coach Horse, with as much beauty, length, and proportion as a foreign Horse, will not act with the same velocity and perseverance, nothing will be more easily answered, without appealing to blood; because we shall find the powers of acting in a foreign Horse much more prevalent, and more equal to the weight of his body, than the powers of acting in a coach Horse:  for whoever has been curious enough to examine the mechanism of different Horses by dissection, will find the tendon of the leg in a foreign Hose is much larger than in any other Horse, whose leg is of the same dimensions; and as the external texture of a foreign Horse is much finer than of any other, so the foreign Horse must necessarily have the greatest strength and perseverance in acting, because the muscular power of two Horses (whose dimensions are the same) will be the greatest in that Horse, whose texture is the finest.