Josh Semalvico London
sextant Josh Semalvico London
record number: 44
instrument type: sextant
manufacturer: Josh Semalvico London
serial number: 650
weight: 1.35 kg
dimensions (l/w/h): 31/12/25 cm
year of manufacture: 1890
instrument set up: on three legs when not in use
handle, held in hand when measuring

The sextant was made around 1890. It is held in the hand with a wooden handle when taking measurements. The reading of the division on the silver-plated metal bracket shall be by means of a vernier with a lens, providing the graduation unit of 15''. The crosshairs consist of two horizontal and two vertical hairs which together form a rectangle. The instrument has a movable mirror with filters for taking a sight of the Sun. It measures the angle between the Sun and the horizon, and with additional data from the almanac and a known instant of the Sun's position, the geographical position can be determined.

The instrument was completely restored, polished and lacquered in 2017.

Characteristics
vertical circle
diameter: unprotected, part of a circle with a division from 0° to 140°
type of division: engraved division
limb implementation: silvered metal bracket
division: sexagesimal/sexadecimal
unit: 15'
Reading
number of reading points: 1
reading device: vernier
number of units: 60
graduation unit: 15''
Telescope
diameter of objective: 16 mm
type: Ramsden's retractable eyepiece
cross hairs/reticule: two horizontal hairs intersecting with two vertical hairs, aiming through the middle of the rectangle