39 Clues _ Cahills vs. Vespers [03] The Dead of Night by Peter Lerangis

some coins that had fallen from Atticus’s pocket. “Hey, I know how it feels. When really bad stuff happens, it’s hard to shake it off.”
    “If Casper even thinks of coming within five miles, he’s toast,” Jake said. “We’ve all got your back, Att. Well, I do, at least.”
    “We do, too,” Amy snapped.
    Atticus nodded. He headed back to the group with Dan, taking deep, cleansing breaths.
    “Plinth?”
Dan said. “Is that like
plinth and needlth
?”
    Atticus smiled. “It means the original foundations. That’s what those low walls are. The library and stuff, they’re all new — including that big fancy door, which leads to the Fakhri sextant.”
    Umarov led the group toward the door, walking between two low, calf-high walls that traced rectangles. “Imagine this empty plateau in the fourteen hundreds, well outside the firelight of Samarkand. So much pure darkness, bright stars! Ulugh Beg cataloged one thousand eighteen of them. Well, some scholars say one thousand twenty-two . . . but who’s counting?”
    The guide pulled the door open. Atticus and Dan raced to the front of the group to get in first. The temperature immediately dropped inside the door, as if the cold of outer space itself had been trapped over the centuries. A narrow stone path led to a wide railing overlooking a deep black hole.
    Atticus’s breath caught in his throat, and it wasn’t because of the temperature. He had seen plenty of photographs of the Fakhri sextant, but they didn’t do justice to the massive sweep of the stone slopes. They plunged into the earth like giant mammoth tusks, with matching stone stairs on either side. He wondered how slabs of such weight and size had been shaped so precisely, polished to a perfect circular curve. He imagined hundreds of slaves hammering through rock, carving stone in the arid heat, using specifications of the tiniest fraction of a circle — using
pi
! Then somehow they had to carry the slabs up a curved slope. And if it was just a centimeter off, the whole thing fell apart. “Whoa . . .” he said.
    “Dude, you could make serious bank with a skateboard rental!” Dan said.
    Amy, who had positioned herself near Dan, jabbed him in the side.
    Umarov cocked his head, bemused. “A gnarly idea, indeed, as they say. Especially as the Fakhri sextant rose much, much higher.” He gestured from the floor way upward behind them. “It curved up past where we are standing . . . into a building with a large dome.”
    Dan craned his neck upward. “Cool.”
    “It traces the north-south meridian exactly,” Umarov said. “Ulugh Beg’s measurements of stars and planets were accurate to one six-hundredth of a degree. This would be the width of an American penny at a distance of a third of a mile.”
    Atticus gazed at the battered, rough walls. Any kind of writing they could have read was gone.
    “So that was it?” Dan said. “They hung out and waited for stars to move?”
    Umarov struck another pose and recited:
    “What of this work of Ulugh Beg,
    Who dared to count infinity?
    His catalog, though vast in scope,
    Yet of divisions, had but three.
    When listed in descending rank,
    The Fakhri apex as a start,
    Descend and rise, descend again,
    And stand thee o’er my ruler’s heart.”
    “What the heck does that mean?” Dan asked.
    Umarov shrugged. “Theories abound. It may have been a key to how he worked. The sextant was indeed Ulugh Beg’s heart. The pendulum descended and rose. The astronomer would stand at the bottom and look up along the shaft, visually lining up the star positions. The bodies were observed each day over many years, and each position was marked. Of course, stars orbit on many planes, so the formulae were complicated. So the ‘divisions’ could be the original buildings of the observatory. ‘Descending rank’ could be the position of the star as the light descends the pendulum. Or a reference to Beg’s many smaller instruments, such as parallactic lineals,