Angels & Demons

arrest."

"No good deed goes unpunished."

Langdon smiled. "So true. And yet Galileo was persistent. While under house arrest, he secretly wrote a lesser-known manuscript that scholars often confuse with Diаlogo. That book is called Discorsi."

Vittoria nodded. "I’ve heard of it. Discourses on the Tides."

Langdon stopped short, amazed she had heard of the obscure publication about planetary motion and its effect on the tides.

"Hey," she said, "you’re talking to an Italian marine physicist whose father worshiped Galileo."

Langdon laughed. Discorsi however was not what they were looking for. Langdon explained that Discorsi had not been Galileo’s only work while under house arrest. Historians believed he had also written an obscure booklet called Diagramma.

"Diagramma della Veritа," Langdon said. "Diagram of Truth."

"Never heard of it."

"I’m not surprised. Diagramma was Galileo’s most secretive work—supposedly some sort of treatise on scientific facts he held to be true but was not allowed to share. Like some of Galileo’s previous manuscripts, Diagramma was smuggled out of Rome by a friend and quietly published in Holland. The booklet became wildly popular in the European scientific underground. Then the Vatican caught wind of it and went on a book-burning campaign."

Vittoria now looked intrigued. "And you think Diagramma contained the clue? The segno. The information about the Path of Illumination."

"Diagramma is how Galileo got the word out. That I’m sure of." Langdon entered the third row of vaults and continued surveying the indicator tabs. "Archivists have been looking for a copy of Diagramma for years. But between the Vatican burnings and the booklet’s low permanence rating, the booklet has disappeared off the face of the earth."

"Permanence rating?"

"Durability. Archivists rate documents one through ten for their structural integrity. Diagramma was printed on sedge papyrus. It’s like tissue paper. Life span of no more than a century."

"Why not something stronger?"

"Galileo’s behest. To protect his followers. This way any scientists caught with a copy could simply drop it in water and the booklet would dissolve. It was great for destruction of evidence, but terrible for archivists. It is believed that only one copy of Diagramma survived beyond the eighteenth century."

"One?" Vittoria looked momentarily starstruck as she glanced around the room. "And it’s here?"

"Confiscated from the Netherlands by the Vatican shortly after Galileo’s death. I’ve been petitioning to see it for years now. Ever since I realized what was in it."

As if reading Langdon’s mind, Vittoria moved across the aisle and began scanning the adjacent bay of vaults, doubling their pace.

"Thanks," he said. "Look for reference tabs that have anything to do with Galileo, science, scientists. You’ll know it when you see it."

"Okay, but you still haven’t told me how you figured out Diagramma contained the clue. It had something to do with the number you kept seeing in Illuminati letters? 503?"

Langdon smiled. "Yes. It took some time, but I finally figured out that 503 is a simple code. It clearly points to Diagramma."

For an instant Langdon relived his moment of unexpected revelation: August 16. Two years ago. He was standing lakeside at the wedding of the son of a colleague. Bagpipes droned on the water as the wedding party made their unique entrance… across the lake on a barge. The craft was festooned with flowers and wreaths. It carried a Roman numeral painted proudly on the hull—DCII.

Puzzled by the marking Langdon asked the father of the bride, "What’s with 602?"

"602?"

Langdon pointed to the barge. "DCII is the Roman numeral for 602."

The man laughed. "That’s not a Roman numeral. That’s the name of the barge."

"The DCII?"

The man nodded. "The Dick and Connie II."

Langdon felt sheepish. Dick and Connie were the wedding couple. The barge obviously had been named in their honor. "What happened to the DCI?"

The man groaned. "It sank yesterday during the rehearsal luncheon."

Langdon laughed. "Sorry to hear that." He looked back out at the barge. The DCII, he thought. Like a miniature QEII. A second later, it had hit him.

Now Langdon turned to Vittoria. "503," he said, "as I mentioned, is a code. It’s an Illuminati trick for concealing what was actually intended as a Roman numeral. The number 503 in Roman numerals is— "

"DIII."

Langdon glanced up. "That was fast. Please don’t tell me you’re an Illuminata."

She laughed. "I use Roman numerals to codify pelagic strata."

Of course, Langdon thought. Don’t we all.

Vittoria looked over. "So what is the meaning of DIII?"

"DI and DII and DIII are very old abbreviations. They were used by ancient scientists to distinguish between the three Galilean documents most commonly confused.

Vittoria drew a quick breath. "Diаlogo… Discorsi… Diagramma."

"D-one. D-two. D-three. All scientific. All controversial. 503 is DIII. Diagramma. The third of his books."

Vittoria looked troubled. "But one thing still doesn’t make sense. If this segno, this clue, this advertisement about the Path of Illumination was really in Galileo’s Diagramma, why didn’t the Vatican see it when they repossessed all the copies? "

"They may have seen it and not noticed. Remember the Illuminati markers? Hiding things in plain view? Dissimulation? The segno apparently was hidden the same way—in plain view. Invisible to those who were not looking for it. And also invisible to those who didn’t understand it."

"Meaning?"

"Meaning Galileo hid it well. According to historic record, the segno was revealed in a mode the Illuminati called lingua pura."

"The pure language?"

"Yes."

"Mathematics?"

"That’s my guess. Seems pretty obvious. Galileo was a scientist after all, and he was writing for scientists. Math would be a logical language in which to lay out the clue. The booklet is called Diagramma, so mathematical diagrams may also be part of the code."

Vittoria sounded only slightly more hopeful. "I suppose Galileo could have created some sort of mathematical code that went unnoticed by the clergy."

"You don’t sound sold," Langdon said, moving down the row.

"I’m not. Mainly because you aren’t. If you were so sure about DIII, why didn’t