The work of the 10,000 horse-power engines of the Great Eastern could be barely equaled by the efforts of 15,000 horses; but to continue their work uninterruptedly, day in and day out, for weeks together, as when done by steam, would require at least three relays, or 45,000 horses. Such a stud would weigh 25,000 tons, and if harnessed "tandem" would extend thirty miles. It is only by such a comparison that the mind can begin to comprehend the utter impossibility of accomplishing by means of animal power the work now done for the world by steam. The cost of the greater power is but about one-tenth that of horse-power, and by its means tasks are accomplished with ease which are absolutely impossible of accomplishment by animal power. It is estimated that the total steam-power of the world is about 15,000,000 horse-power, and that, were horses actually employed to do the work which these engines would be capable of doing were they kept constantly in operation, the number required would exceed 60,000,000. Thus, from the small beginnings of the Comte d'Auxiron and the Marquis de Jouffroy in France, of Symmington in Great Britain, and of Henry, Rumsey, and Fitch, and of Fulton and Stevens, in the United States, steam-navigation has grown into a great and inestimable aid and blessing to mankind. We to-day cross the ocean with less risk, and transport ourselves and our goods at as little cost in either time or money as, at the beginning of the century, our parents experienced in traveling one-tenth the distance. It is largely in consequence of this ingenious application of a power that reminds one of the fabled genii of Eastern romance, that the mechanic and the laborer of to-day enjoy comforts and luxuries that were denied to wealth, and to royalty itself, a century ago. The magnitude of our modern steamships excites the wonder and admiration of even the people of our own time; and there is certainly no creation of art that can be grander in appearance than a transatlantic steamer a hundred and fifty yards in length, and weighing, with her stores, five or six thousand tons, as she starts on her voyage, moved by engines equal in power to the united strength of thousands of horses; none can more fully awaken a feeling of awe than an immense structure like the great modern iron-clads (Fig. 145), vessels having a total weight of 8,000 to 10,000 tons, and propelled by steam-engines of as many horse-power, carrying guns whose shot penetrate solid iron 20 inches thick, and having a power of impact, when steaming at moderate speed, sufficient to raise 35,000 tons a foot high. Far more huge than the Monarch among the iron-clads even is that prematurely-built monster, the Great Eastern (Fig. 147), already described, an eighth of a mile long, and with steam doing the work of a stud of 45,000 horses.