The journey on the Apure was largely occupied by Humboldt in the adding to his collections of specimens and making drawings of every object of importance, and was thus very rich in scientific interest.

When they reach the Orinoco, whose broad expanse of waters stretched before them like a sea, they had still greater opportunities for studying ht characteristics of South American scenery, and during their progress a remarkable rise in the river gave a fine chance for making observations on the water-levels.

While on this river they landed on an island owned by one of the Spanish missions, and found that they were considered as suspicious characters by the priests, who could not imagine that they had really left the comforts of home and undertaken the dangers of an unknown country merely for the sake of making botanical collections and measuring the land.

The great waterfalls in the Orinoco were a source of deep interest to Humboldt, who took the opportunity of measure the height of the falls and comparing it with other celebrated cataracts; the noise of the falls was also made a subject of investigation, and as in the solitude of such a region the quiet of the day is never disturbed, Humboldt came to the conclusion that the increased loudness at night was due to the fact that the cold air conducted the sound more perfectly than the warm air of the day.

Humboldt stayed among the waterfalls five days, studying their physical characteristics, and then proceeded on his journey toward the Cassiquiare, which unites the Orinoco with the Rio Negro. He reached the latter stream in due time, but found the passage of it the most difficult in his journey, as the swarms of poisonous insects, a and the impenetrable thickets which lined the shores, made both rowing and landing equally hard. They had to cut a landing place with their axes, while the dampness of the wood, owing to the great amount of sap, made it almost impossible for them to obtain a fire.

But at last the passage was over, and Humboldt felt amply rewarded for all the hardships he had endured when he found that he had actually traced the connection between the Orinoco and the Rio Negro. This event was of the greatest importance to the travelers, as it enabled them to solve the mystery that had hitherto hung over those almost inaccessible regions. The possibility of traveling by water from the Orinoco to the Amazon had been a matter of doubt to Europeans, and the voyage of Humboldt was of the greatest scientific interest, as it settled the question definitely. The drawings which Humboldt made were used to correct the old charts, and the societies of Europe were loud in their praise of the man who had ventured on such a perilous journey for the sake of science.

At this place, also, Humboldt collected some valuable materials for illustrating the peculiar formation of the soil, and was able, from the experience gained, to hint at some general laws of nature in distributing the veins of water over the globe. Having accomplished the great object of his journey, Humboldt now left the region which h had hitherto been regarded as almost mythical by Europeans, and returned to Cumana.

Humboldt now arranged to undertake a expedition to include visits to Cuba, Mexico, the Philippine Islands, India, and Turkey, and as the first stage of the journey, sailed with Bompland for Cuba, reaching Havana a month after leaving Cumana.

They remained in Cuba several months, studying the soil, climate, and vegetation, making many valuable additions to their botanical collections, and observing the condition of the slaves. But the great journey that had been planned was never undertaken, as in Cuba Humboldt heard that a friend with whom he had promised to travel through Chili and Peru, had sailed from France for Buenos Ayres, and he at once determined to return to South America and join him. But on reaching Carthagena, they learned that the season was too far advanced for a voyage on the Pacific, and resolved to occupy their time during the necessary delay by a journey up the Magdalena, hoping to enrich his collections by some rare specimens.

In this he was not disappointed, for they found the botanical treasures of this region equal to those in the Orinoco valley, and in addition to this work, Humboldt was able to make a chart of the river district, another great gift to geographical science.

When this had been accomplished, they left the Magdalena and proceeded overland to Quito, which they reached four months after leaving Carthagena.

The journey was difficult, as the was led through an almost pathless region, but Humboldt improved his time by studying the formation of the rocks and waterfalls, mines, remains of earthquakes, the soil, and the now-covered volcanoes and mountain passes; and although they arrived at Quito in an almost exhausted condition, they considered this part of their experience in South American travel as invaluable. The delightful situation of Quito, with its agreeable climate and beautiful surroundings, soon brought back health and good spirits to the travelers.

The ranges of lofty, snow-capped mountains which bounded the horizon roused anew the love for scientific research, and preparations were made for the ascent of Chimborazo and Cotopaxi.

The volcano of Cotopaxi had always been noted for its terrific eruptions, and the visit of Humboldt to its crater was anticipated with unusual interest by the inhabitants of that region. Humboldt had already found the crater of Pichincha inflamed, and bare of the snow which had filled it so long, a circumstance which excited general alarm in Quito, as indicative of another eruption, and any appearance of danger in the neighborhood of Cotopaxi would have been regarded with even more dread. In 1738 the flames from this volcano had risen above the crater in a ring measuring nearly three thousand feet in circumference; two years later another eruption occurred, the noise of which was heard two hundred miles away; a still later outburst there so many ashes in the air that it was dark for several hours, and the inhabitants of the villages near were obliged to go about with lanterns; but at the time of Humboldt's visit the snow still lay in gleaming masses on the summit, and as it was impossible to reach the brim of the crater he was unable to make the scientific experiments he had anticipated.

He was also unable to reach the extreme point of Chimborazo, as a bottomless chasm stretched directly across his path, but he reached an altitude never before attained by any human being, pushing on his way even after reaching a point where the mercury froze in the thermometer and the blood gushed from the nostrils of the adventurous travelers.

Humboldt now made various tours, fruitful in scientific interest, during which he examined the flora of the district, visited the remains of the great aqueduct of the Incas, and corrected the chart of the Amazon which had been made by a French astronomer, but which Humboldt found to be full of errors. Their travels finally brought them to Lima, where they were able to make some important observations on the climate and in astronomy, remaining there several months for that purpose.

From Lima they sailed for Mexico, and as they passed the snowy peaks of the group an ominous sound reached their ears. It was the roar of Cotopaxi, fifty miles distant, whose snow-capped summit had vanished in a single night, and whose thunderings reached they day and night when they were far away on their journey.

Humboldt carried away from South America a picture so vivid and startling that he said, in after-years, it was only necessary to close his eyes to shut out surrounding objects, to see again the foamy waves of the Orinoco, down which he glided, followed they the shrieks of the jaguars; or the treeless stretches of the llanos, where the moss-covered huts of the inhabitants lie miles apart, and the crocodile and boa, curried deep in the soil, sleep through the long seasons of drought—while the horses and cattle wander about roaring in agony, and the burnt grass falls in dust on the parched ground.

During his journey he had suffered from extremes of heat and cold unknown in the temperate zone; he had lived in solitudes where only plants and animals flourished, and where the foot of main had never trodden before; he had been exposed to ravenous beasts, and had found danger even in the trailing vines and beautiful flowers whose poisonous breath touched him as he passed, but through it all his courage never faltered, and his work for science still went on.

And seldom has it been the fortune of the traveler to open such a world of unexplored beauty to the eye of the untravelled.

South America, with its mighty rivers, lofty mountain-ranges, picturesque inland lakes, its llanos, varying from scenes of desolation to the luxuriant beauty of tropical vegetation; with its fabulous mineral wealth, its forests of mahogany and rosewood, its vast herds of horses and cattle roaming in undisturbed freedom over the immense plains; its flourishing cities, in strange contrast to the secluded missions that were scattered in places remote from the world, its ruins of old Peruvian towns, and remains of a dead civilizations, were all calculated to inspire the mind of a traveler like Humboldt—and when to this was added the knowledge that all this beauty of city and plain lay at the mercy of the dreaded earthquake and volcano, which were liable at any time to destroy it forever, the interest could not fail to be increased.

In Mexico Humboldt's most important scientific work consisted in certain astronomical observations by which he arrived at the correct longitude of the city of Mexico, which had until then been wrongly given on the maps. He also visited the celebrated mines of that country, devoting much time to the study of the ores, and made important observations on the formations of the volcanoes of the region; the antiquities of Mexico were also a source of great interest to the travelers, and much time was spent in examining them and transcribing the descriptions to their journals.

At last the great American journey came to an end, and, after a short trip to the United States by the way of Havana, Humboldt sailed for France and reached Bordeaux in August, 1804, five years after his departure from European shores.