Henry Hindley (1701–1771), a clockmaker, watchmaker, and maker of scientific instruments, was born in Wigan and worked in York from 1731 until his death. This instrument is believed to be the world’s first equatorially-mounted telescope.

Overall Description

The instrument comprises a brass refracting telescope with a micrometer box, which contains moveable wires that form a square reticle within the field of view. The purpose of the micrometer box is to measure angular distance.

The instrument is of particular interest because of the use of worm gears of an enveloping or globoidal form. In engineering, this design of gear is widely referred to as the Hindley Worm.

This telescope was described by John Smeaton in a paper read at the Royal Society on 17 November 1785, entitled: Observations on the Graduation of Astronomical Instruments, with an Explanation of the Method Invented by the Late Mr Henry Hindley of York, Clockmaker, to Divide Circles into Any Given Number of Parts.

Context

This instrument is a product of the European Age of Enlightenment, reflecting a period of dramatically expanding interest in scientific endeavour both professionally and by amateurs. Having timed a transit of Mercury in St Helena in 1677, Edmond Halley discussed the possibility of using transits of Mercury or Venus to determine the solar parallax and, hence, the distance from the Earth to the Sun. Halley believed that the geometry of Venus’s transits was much more likely to produce accurate results and promoted the idea in papers presented to the Royal Society in 1691 and 1694.

Hindley’s instrument combined astronomical and terrestrial functionality. By placing the telescope on his own design of a universal mount, it could not only be used for observations of the forthcoming Transit of Venus study but also for surveying land, making it particularly appealing to the likes of William Constable.

Mount

The mount comprises an upper Declination Circle over an Equatorial Circle above a Meridian Circle. The whole rotates about a vertical axis via a Setting Circle mounted between the tripod legs. The positioning of all four circles is via worm wheels of enveloping hourglass form, engaging with throated gears cut into the edges of the Circles. All four worm gears are set in pivoted, sprung frames that can be latched out of engagement for rapid setting. The flanks of the threads are tapered. The worm and worm wheel are pushed together in use by leaf springs, eliminating backlash. The equatorial worm is fitted with a universal joint and square female socket, presumably for a hand wheel, crank, or clock drive.

Telescope

The 825mm-long, brass-bodied refracting telescope, with a focal length of 2’ 7”, has a micrometer box towards the eyepiece end. The objective end has a dew shade and a push-fit dust cap. The eyepiece has a sliding dust cover.

Lenses

The telescope’s optics comprise four lenses. The objective lens is a doublet, 46mm in diameter. Focusing is achieved by turning a winding wheel on the micrometer box.

Micrometer Box

The micrometer box is approximately 80mm square with two hand-operated knurled wheels. One wheel, set on one of the box edges, is for focusing the telescope. The other, the reticle setting wheel, is in the centre of a face of the box, opposite the engraved scale and signature. The setting wheel is for adjusting the four wire frames and is geared to a blued steel indicator hand, with a corresponding engraved graduated scale. The face of the box with the graduated scale is signed below the centre: Hindley, YORK.

Telescope Mount and Frame

The telescope is mounted in an open brass frame, retained by two split clamps that allow the telescope to be rotated about its axis within the frame. The frame incorporates a pivoted spirit bubble mounted parallel with the telescope tube.

The mounting frame, tube, bubble, and worm gear are mounted on a frame pivoting about the central axis of the Declination Circle.

Conclusion

Although the instrument was ultimately unsuccessful, partly due to the flexibility of the telescope mounts and limitations of the optics, the globoidal worm gear elements of the instrument remain influential today in gear design.