"What's that to do with the crow?" Fred asked. "Why, everything," Frank answered; "the crow makes ye-caw-go, doesn't it?" "Now, Frank," the Doctor said, as he laughed over the conundrum, "making puns when we're a thousand miles from home and going west! However, that will do for a beginner; but don't try too often." Fred thought he must say something, but was undecided for a moment. The room was open, and as he looked into the hall, he saw the chambermaid approaching the opposite door with the evident intention of looking through the keyhole. This gave him his opportunity, and he proposed his question. "Why are we like that chambermaid over there?" "The Doctor and Frank couldn't tell, and Fred answered, triumphantly, "Because we're going to Pek-in." "I think you boys are about even now," said the Doctor, "and may stop for the present." They agreed to call it quits, and resumed their study of the map. [Illustration: FROM CHICAGO TO SAN FRANCISCO.] They decided to go by the Northwestern Railway to Omaha. From the latter place they had no choice of route, as there was only a single line of road between Omaha and California. [Illustration: OMAHA.] From Chicago westward they traversed the rich prairies of Illinois and Iowa--a broad expanse of flat country, which wearied them with its monotony. At Omaha they crossed the Missouri River on a long bridge; and while they were crossing, Frank wrote some lines in his note-book to the effect that the Missouri was the longest river in the world, and was sometimes called the "Big Muddy," on account of its color. It looked like coffee after milk has been added; and was once said by Senator Benton to be too thick to swim in, but not thick enough to walk on. Now they had a long ride before them. The Union Pacific Railway begins at Omaha and ends at Ogden, 1016 miles farther west. It connects at Ogden with the Central Pacific Railway, 882 miles long, which terminates at San Francisco. As they rode along they had abundant time to learn the history of the great enterprise that unites the Atlantic and Pacific coasts, and enables one to travel in a single week from New York to San Francisco. The Doctor had been over the route previously; and he had once crossed the Plains before the railway was constructed. Consequently, he was an excellent authority, and had an abundant store of information to draw from. "The old way of crossing the Plains and the new way of doing the same thing," said Doctor Bronson, "are as different as black and white. My first journey to California was with an ox wagon, and it took me six months to do it. Now we shall make the same distance in four days." "What a difference, indeed!" the boys remarked. [Illustration: ATTACKED BY INDIANS.]