The tubes had yet to be filled and there was no hint of what they were to be filled with.

“What I am wondering about is why they troubled to send the tubes at all?” said Fairbairn slowly.  “There’s some reason, of course, something perhaps in the make of the glass.”

He held one of the tubes up to the light.  There was nothing to distinguish it from any one of the tubes in which small tabloids are sold by chemists.

Hillyard got out of his bureau the letter in which these tubes were mentioned.

“‘They have been successful in France,’” he said, quoting from the letter.  “The scientists may be able to make something of them in Paris.  This letter and the tubes together may give a clue.  I think that I had better take one of the boxes to Paris.”

“Yes,” said Fairbairn gloomily.  “But——­” and he shrugged his shoulders.

“But it’s one of the ninety per cent, which go wrong, eh?” Hillyard finished the sentence with bitterness.  Disappointment was heavy upon both men.  Hillyard, too, was tired by the tension of these last sleepless days.  He had not understood how much he had counted upon success.

“Yes, it’s damnably disheartening,” he cried.  “I thought these tubes might lead us pretty straight to B45.”

“B45!”

The exclamation came from Jose Medina, who was leaning against the doorpost of the saloon, half in the room, half out on the sunlit deck.  He had placed himself tactfully aloof.  The examination of the cases was none of his business.  Now, however, his face lit up.

“B45.”  He shut the door and took a seat at the table.  “I can tell you about B45.”

CHAPTER XVIII

THE USES OF SCIENCE

It was Hillyard’s creed that chance will serve a man very capably, if he is equipped to take advantage of its help; and here was an instance.  The preparation had begun on the morning when Hillyard took the Dragonfly into the harbour of Palma.  Chance had offered her assistance some months later in an hotel at Madrid; as Medina was now to explain.

“The day after you left Mallorca,” said Jose Medina, “it was known all over Palma that you had come to visit me.”

“Of course,” answered Martin.

“I was in consequence approached almost immediately, by the other side.”

“I expected that.  It was only natural.”

“There is a young lady in Madrid,” continued Jose Medina.

“Carolina Muller?”

“No.”

“Rosa Hahn, then.”

“Yes,” said Jose Medina.

Jose rose and unlocking a drawer in his bureau took out from it a sheaf of photographs.  He selected one and handed it with a smile to Hillyard.  It was the portrait of a good-looking girl, tall, dark, and intelligent, but heavy about the feet, dressed in Moorish robes, and extended on a divan in Oriental indolence against a scene cloth which outdid the luxuries of Llalla Rookh.