The telescope increases the apparent size of distant objects, so making them to appear nearer. A crude form was in use before 1570. In 1608, two Dutch spectacle makers, Jansen and Lippershey, designed and built three instruments ‘for seeing at a distance’. Galileo improved on these by using double concave eyepieces. He built his first optical instrument, to which he gave the name ‘telescope’, in 1609. Galileo immediately turned his telescope on the heavens, but the military applications for something that provides a magnified view of things far off were obvious.
Sailors seized on the telescope's possibilities almost at once. However, the term ‘telescope’ was not in naval use until 1744 when Murdoch Mackenzie referred to the instrument in his treatise on surveying. The telescope, usually referred to in the navy as a glass, extended the effective range of vision of the lookouts who were so vital to naval warfare since spotting the enemy in the midst of a vast ocean was a necessary prelude to avoiding or bringing the enemy to battle. It made the observation of the signals, the principal method of ship-to-ship communication, more effective—or not, in the case of Adm Horatio Nelson. During the battle of Copenhagen of 1801, Nelson's superior Sir Hyde Parker signalled the recall imperilling the success of the British fleet. Nelson put his telescope to his blind eye and murmured: ‘I really do not see the signal!’ and ignored it, turning possible disaster into triumph. Telescopes were also widely used in land warfare.
The principle of the telescope has also been adapted to other military uses. A terrestrial telescope with sharply defined markings placed in one of its image planes can be fitted to a weapon to offer magnification of the target and enhance accuracy. Such ‘telescopic sights’ are a feature of sniper rifles.
A refinement of telescope is the binocular telescope or binoculars as they are more common called. The binocular consists of two similar telescopes provided with two prisms, one for each mounted on a single frame. A single thumbscrew may control the focus of both telescopes simultaneously and provision may be made for focusing each separately to allow for varying characteristics in the two eyes. Compact, handy, and allowing better stereoscopic effect, that is depth perception to greater distances than the telescope, the binoculars have become an absolutely standard piece of military equipment, commonly carried by officers and vehicle commanders.
— Chris Mann
