Hadley's first reflecting quadrant was a simple device with a frame spanning a 45° arc. In the image at the right, from Hadley's article in the "Philosophical Transactions" of the Royal Society, you can see the nature of his design. A small sighting telescope was mounted on the frame along one side. One large "index mirror" was mounted at the point of rotation of the index arm. A second, smaller "horizon mirror" was mounted on the frame in the line of sight of the telescope. The horizon mirror allows the observer to see the image of the index mirror in one half of the view and to see a distant object in the other half. A shade was mounted at the vertex of the instrument to allow one to observe a bright object. The shade pivots to allow it to move out of the way for stellar observations.