An intriguing and classic explorerâ€™s and navigatorâ€™s tool. Essential instruments â€“ A compass, a sextant and a telescope. The telescope consists of a wood barrel holding an objective, a system of lenses. It is protected by brass collars and a decorative brass cap. To use, pull out the brass tubes (called drawers in Britain). The smallest tube holds the eye objective. Judiciously push in the smallest end-tube to focus.