"Across the ocean?" queried Mark, quickly.

"I do not see why any one could not take a trip to the other side of the Atlantic in your 'plane," replied the professor. "With proper precautions, of course."

They reached the land and came safely to rest before the hangar without further accident. The professor was delighted with the working of his catapult and at once made ready to call the attention of the Navy Department to his improvement in the means of launching an airship from the deck of a vessel. Ere he had written to the Department, however, he and his young friends were suddenly made interested in a scheme that was broached by letter to Professor Henderson from a fellow-savant, Dr. Artemus Todd, of the West Baden University.

Professor Henderson and Dr. Todd had often exchanged courtesies; but the university doctor was mainly interested in medical subjects, while Mr. Henderson delved more in the mysteries of astronomy and practical mechanics.

The doctor's letter to Professor Henderson read as follows:

"Dear Professor:

"I am urged to write to you again because of something that has recently come to my knowledge regarding a subject we once discussed. As you know, for some years past I have been investigating not the cause of aphasia and kindred mental troubles (for we know the condition is brought about by a clot of blood upon the brain), but the means of quickly and surely overcoming the condition and bringing the unfortunate victim of this disorder back to his normal state. In our age, when mental and nervous diseases are so rapidly increasing, aphasia victims are becoming more common. Scarcely a hospital in the land that does not have its quota of such patients under treatment—patients who, in many cases, have completely forgotten who and what they are and have assumed a totally different identity from that they began life with."

"We know that, in some cases, hypnotism has benefited the aphasia and amnesia victim. His condition is not like that of the mentally feeble; he has merely lost his memory of what and who he previously was. Believing that all disease, of whatsoever nature, can be safely treated only through the blood, this ill to which human flesh is heir particularly must be treated in that way, for we know that a stagnant state of the blood in one spot, at least, is the cause of the patient's malady. Therefore I have been experimenting botanically to discover a remedium for the state in question—something that will act swiftly upon the blood, and directly dissipate such a clot as is spoken of above."

"My dear Professor! I can announce with joy that this remedium is discovered. I obtained a specimen of a very rare plant brought back from Alaska by a miner who wandered into the fastnesses of the Endicott Range, far beyond the usual route of gold miners and in a district which, I understand, is scarcely ever crossed by whites and which is, indeed, almost impassable, even in the summer months. With the aid of this herb—Chrysothele-Byzantium (it was known to the ancients, but very rare)—I have brewed a remedium which, in one case at lest, instantly cleared the blood vessels of the patient and brought him back to a knowledge of his real self."

"But my supply of the herb is gone. It reached me in its dry state, or I should have first tried to propagate it. It seeds but once in seven years and therefore is rare and hard to grow. But I must have a supply of the Chrysothele-Byzantium seeds, plants, and all. I look to you, my dear Professor Henderson, for help. To you space and the flight of time are merely words. You can overcome both if you try. I need somebody to go to the northern part of Alaska—that is, beyond the Endicott Range—to obtain this rare plant for me. You have already flown over the North Pole and a trip which carries one only three or four degrees beyond the Arctic Circle is a mere bagatelle to you."