When Russia, determined to establish a port on the open sea, though it were thousands of miles from her capital, built the great Trans-Siberian Railway, she progressed rapidly with her fragile, light-rail, single-track road until she came to Lake Baikal. Here Nature had placed what might well be deemed an impossible obstruction: a huge inland lake four hundred miles in length, eighteen hundred feet deep, bordered with mountains, whose sheer granite cliffs rose from the water to a height of fifteen hundred feet, and in their turn were overshadowed by snow-capped peaks. The lake at this point is forty miles wide. No bridge could span its storm-swept surface, no tunnel could be driven beneath its sombre depths. How was the obstacle to be surmounted? A weaker nation would have given up the task, as the French tired of working at the Panama Canal; Russia, ponderous, tireless, determined, almost irresistible, moved on. In the science of Physics, the momentum of a moving body is thus analysed and expressed: M = _m_ × _v_. In other words, it equals the mass of the body multiplied by its velocity. If either factor be increased, the momentum becomes correspondingly greater. When Russia moves, the velocity is slight, but the mass is enormous. When the soldier, in the time-worn anecdote, tried to stop with his foot the slowly rolling spent cannon-ball, it snapped his leg like a pipe-stem. The nation that opposes Russia must itself be of iron mould, or it will snap. Lake Baikal was a trifle, a mere incident to the civil engineers who laid out the Trans-Siberian Railway. In the summer-time huge steam ferry-boats plied from shore to shore, transferring passengers and freight from the western to the eastern or Trans-Baikal section. From November to April the lake is frozen over, but during at least half of that time enormous ice-breakers, like the heaviest ocean-going tug-boats, crashed through the ice and kept open a canal from side to side. These were temporary expedients. The engineers meanwhile had not been idle. They attacked the cliffs bordering the southern end of the lake, and began cutting a path through the solid rock for advancing Russia. Twenty-seven tunnels were to be bored, and have since been completed. While Ivan waited by the shore a dull boom came now and then to his ear, from the blasting. It was the relentless, unfaltering tread of Russia's iron heel. But other means had to be provided, in that terrible winter of 1903, for the passage of troops and supplies, for although the great mass of soldiers did not understand, their leaders and the counsellors of state in St. Petersburg knew there was urgent need. A railroad was begun upon the ice itself, and before March was in actual operation. A thousand feet of water gloomed beneath the thin ice bridge. Once or twice there was an accident--a locomotive went through, or a few cars, and, incidentally, a few human beings. This was nothing. "Forward, my men! It is the Czar's command!"