Dr. Wolf's little steamer puffed up the big Sankuru River, threading its way among many islands, and revealing a great new highway and many unaccustomed sights. One day Dr. Wolf was astounded to see, some ways up the river, what appeared to be a raging snow-storm. Of course snow never falls there, but the illusion was perfect. It was caused by myriads of white butterflies zigzagging through the air. Two or three years later a black boy named Pitti, who had been taken from his home on this river to Germany, came rushing to his friends, exclaiming; "Oh, look out of the window! The air is full of butterflies." It was snowing hard. You see, the first impressions both of the learned doctor and of the ignorant little black boy were erroneous, because neither of them was in a country that he knew very well. You will see on your map that the great northern bend of the Congo is like a bent bow, and far below it is the string of the bow--the Sankuru--pieced out at one end by the Kassai River, which unites it with the Congo, while the other end stretches far across, almost to the other end of the bow. Dr. Wolf's discovery added almost 800 miles of navigable waters to the Congo basin, stretching almost due east to central Africa. Many a boy who loves adventure would think it a proud honor to add so important a fact to geographic knowledge, but I wonder how many boys would be willing to pay the great price that Dr. Wolf and all the pioneer explorers have had to pay for the discoveries that made them famous.