Mount Wilson Observatory convoy

July 1, 1917. Nearly 200 men accompanied the truck as it made the 8-hour trip at an average speed of about one mile per hour. Many of them held ropes attached to the truck as it negotiated the many switchbacks. Others were there to protect the precious cargo from another potential danger: a caller the day before had threatened to blow up the mirror while it was en route to the mountain. Photo: Carnegie/ Huntington Library