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Binocular telescopes, or binoculars (also known as field glasses), are two identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects.

Binocular Telescope

Binocular telescopes, or binoculars (also known as field glasses), are two identical or mirror-symmetrical…

Boulanger succeeded in producing a binocular of an entirely new type in 1859.

Binoculars

Boulanger succeeded in producing a binocular of an entirely new type in 1859.

The model of binoculars invented by E. Abbe.

Binoculars

The model of binoculars invented by E. Abbe.

"Dollond's divided object-glass heliometer of the third type. A is the end of the reflecting telescope, upon which the adapter B is fitted. B carries a wheel (not seen in the figure) formed of a ring racked at the outer edge, and fixed to the brass plate CC, so that the pinion moved by the handle D may turn it into any position. Two plates F, G, with the attached semi-lenses, move in slides fixed to the plate CC, —simultaneous motion, in contrary directions, being communicated to them by turning the handle E, which drives a concealed pinion that works in the two racks seen in the highest part of the figure." —The Encyclopedia Britannica, 1903

Heliometer

"Dollond's divided object-glass heliometer of the third type. A is the end of the reflecting telescope,…

Sir William Herschel, famous English astronomer

Sir William Herschel

Sir William Herschel, famous English astronomer

An illustration of a jester looking through a telescope.

Jester Looking Through Telescope

An illustration of a jester looking through a telescope.

"Sir David Gill devised a measuring machine which combines the rapidity of the glass—scale micrometer with the accuracy of the spider—line micrometer and simplifies the reductions of the observations at the same time." —Encyclopaedia Brittannica, 1910

Gill's Measuring Machine for Micrometer

"Sir David Gill devised a measuring machine which combines the rapidity of the glass—scale micrometer…

An illustration of a man sitting in a chair holding a small telescope.

Man in Chair

An illustration of a man sitting in a chair holding a small telescope.

"The horizontal section in the direction of the axis of the telescope. The eye-piece ab consists of two planoconvex lenses a, b, of nearly the same focal length, and with the two convex sides facing each other. They are placed at a distance apart less than the focal length of a, so that the wires of the micrometer, which must be distinctly seen are beyond b. The eye-piece slides into the tube cd, which screws into the brass ring ef, through two openings in which the oblong frame, containing the micrometer slides, passes." —The Encyclopedia Britannica, 1903

Micrometer

"The horizontal section in the direction of the axis of the telescope. The eye-piece ab consists of…

"The vertical section in the direction of the axis of the telescope. The eye-piece ab consists of two planoconvex lenses a, b, of nearly the same focal length, and with the two convex sides facing each other. They are placed at a distance apart less than the focal length of a, so that the wires of the micrometer, which must be distinctly seen are beyond b. The eye-piece slides into the tube cd, which screws into the brass ring ef, through two openings in which the oblong frame, containing the micrometer slides, passes." —The Encyclopedia Britannica, 1903

Micrometer

"The vertical section in the direction of the axis of the telescope. The eye-piece ab consists of two…

"a is the sphere, placed in half-holes on the axis bb, so that when its principal axis is parallel to the axis the telescope it gives only one image of the object. In a direction perpendicular to that axis it must be so placed that when it is moved by rotation of the axis bb the separation of the images shall be parallel to that motion. The angle of rotation is measured on the grduated circle C. The angle between the objects measured is = r sin 20, where r is a constant to be determined for each magnifying power employed." —The Encyclopedia Britannica, 1903

Micrometer

"a is the sphere, placed in half-holes on the axis bb, so that when its principal axis is parallel to…

"a is the sphere, placed in half-holes on the axis bb, so that when its principal axis is parallel to the axis the telescope it gives only one image of the object. In a direction perpendicular to that axis it must be so placed that when it is moved by rotation of the axis bb the separation of the images shall be parallel to that motion. The angle of rotation is measured on the grduated circle C. The angle between the objects measured is = r sin 20, where r is a constant to be determined for each magnifying power employed." —The Encyclopedia Britannica, 1903

Micrometer

"a is the sphere, placed in half-holes on the axis bb, so that when its principal axis is parallel to…

A Repsolds micrometer used by Cape Observatory. The large micrometer is used to accurately adjust the telescope by series of knobs and screws.

Repsolds Micrometer in Cape Observatory

A Repsolds micrometer used by Cape Observatory. The large micrometer is used to accurately adjust the…

A micrometer with the box removed from Cape Observatory. The device rotates the telescope accurately by turning the wheels. This view of the micrometer is attached to the base.

Repsolds Micrometer with Removed Box Cape Observatory

A micrometer with the box removed from Cape Observatory. The device rotates the telescope accurately…

"Repsolds' more recent form of the spider—line micrometer (since 1893) for large telescope. Quick motion in Position—angle for rough setting or for the measurement of close double stars is given by the large ring R." —Encyclopaedia Britannica, 1910

Repsolds Spider Line Micrometer for Quick Position Angle Motion

"Repsolds' more recent form of the spider—line micrometer (since 1893) for large telescope. Quick…

"C. Collimator; P, center of group of prisms; T, telescope; s, slit through which the ray of light enters, R, ray on its progress through prisms to telescope."—Finley, 1917

Spectroscope

"C. Collimator; P, center of group of prisms; T, telescope; s, slit through which the ray of light enters,…

The apparatus is used to apply the spirit-level to land-surveying.

Spirit-level with Telescope

The apparatus is used to apply the spirit-level to land-surveying.

Still life arrangement including a globe, telescope, book, right angle, rolled map, and dividers.

Still Life with Globe and Telescope

Still life arrangement including a globe, telescope, book, right angle, rolled map, and dividers.

This illustration shows a Surveyor's, or Y-level. In use, the telescope is set perfectly horizontal and pointed back at a rod placed vertically at the starting point. The rod is graduated and after a reading has been taken of the height above the ground cut by the cross wires of the telescope, it is moved to a point forward of the instrument, which is then revolved in a horizontal plane and a reading taken of the rod in its new position. The difference in level is obtained from the difference in readings of the two points, and subsequent readings are taken by removing the level, sighting on the rod in its second position, and then repeating the operation, the readings in this case being recorded.

Surveyor's Level

This illustration shows a Surveyor's, or Y-level. In use, the telescope is set perfectly horizontal…

An optical instrument employed in viewing distant objects, as the heavenly bodies.

Telescope

An optical instrument employed in viewing distant objects, as the heavenly bodies.

"A telescope is an instrument designed for the observation of distant objects, and consists essentially of an objective for the formation of an image of the object and of an eyepiece for magnifying this image." — Avery, 1895

Telescope

"A telescope is an instrument designed for the observation of distant objects, and consists essentially…

"The following description of a section of Lord Rosse's telescope, though not so perfect as could be desired, is the best we could obtain. it exhibits a view of the inside of the eastern wall, with the tube, and machinery by which it is moved. A is the mason-work on the ground; B the universal joint, which allows the tube to turn in all directions; C the speculum in the tube; E the eye-piece through which the observer looks; F a pulley by which the tube is moved; H a chain attached to the pulley, and to the side of the tube; I, a chain running to K, the counterpoise; L, a lever connecting the chain M with the tube; Z another chain which passes from the upper part of the tube over a pulley at W, (not seen) and crosses to the opposite wall; X a railroad on which the speculum is drawn either to or from the tube. The dotted line H, shows the course of the weight R, as the tube rises or falls. The tube is moved from wall to wall by a ratchet wheel at R, which is turned by the lever O, on the circle N, the ends of which are fixed in the two walls." —Comstock, 1850

Telescope

"The following description of a section of Lord Rosse's telescope, though not so perfect as could be…

"The eye-end of a telescope. The reader will recognize the micrometer previously described. L is a paraffin lamp fitting by a bayonet joint into a copper cover c. This effectually defends its glass chimney against accident, and protects the lamp from wind. The simple means by which this lamp is made to preserve its verticality in all positions of the telescope is evident from the figure. By this lamp alone the bright wire or bright field illumination is given at pleasure, and with any desired intensity, simply by movement of the small pin p." —The Encyclopedia Britannica, 1903

Telescope

"The eye-end of a telescope. The reader will recognize the micrometer previously described. L is a paraffin…

"These telescopes were all reflectors; that is, instead of looking up at a star through a tube with a glass in the upper end [Herschel] would look down into the tube away from the star and see its reflecting in a concave mirror at the lower end of the tube."—The Foundation Library, 1911

A Great Reflecting Telescope

"These telescopes were all reflectors; that is, instead of looking up at a star through a tube with…

"The micrometer box, and of course with it the whole system of spider webs, is moved by the screw s, whilst the measuring web is independently moved by the screw S." —Encyclopaedia Brittannica, 1910

Repsolds Micrometer Box for Telescope Cape Observatory

"The micrometer box, and of course with it the whole system of spider webs, is moved by the screw s,…

"The inversion of the object is of little consequence when the instrument is employed for astronomical purposes, for since the forms of the heavenly bodies are spherical, their positions, in this respect, do not affect their general appearance. But for terrestrial purposes, this is manifestly a great defect, and therefore those constructed for such purposes, as ship, or spyglasses, have two additional lenses, by means of which, the images are made to appear in the same position as the objects. These are called double telescopes." -Comstock 1850

Double Refracting Telescope

"The inversion of the object is of little consequence when the instrument is employed for astronomical…

"The Galilean telescope has a double-concave eye-lens that intercepts the rays before they reach the focus of the objective." — Avery, 1895

Galilean Telescope

"The Galilean telescope has a double-concave eye-lens that intercepts the rays before they reach the…

A Repsolds micrometer box for Yerkes Telescope. The wheels on the sides adjusts the telescope sideways, up, and down accurately.

Repsolds Micrometer Box for Yerkes Telescope

A Repsolds micrometer box for Yerkes Telescope. The wheels on the sides adjusts the telescope sideways,…

"The reflecting telescope has an objective a concave mirror, tecnically called a speculum. The images formed by the speculum are brought to the eyepiece in several different ways. Sometimes the eyepiece consists of a series of convex lenses placed in a horizontal tube." — Avery, 1895

Reflecting Telescope

"The reflecting telescope has an objective a concave mirror, tecnically called a speculum. The images…

"The most simple refracting telescope consists of a tube, containing two convex lenses, the one having a long, and the other a short, focal distance." -Comstock 1850

Refracting Telescope

"The most simple refracting telescope consists of a tube, containing two convex lenses, the one having…

"Suppose a, to be a distinct object, from which pencils of rays flow from every point toward the object lens b. The image of a, in consequence of the refraction of the rays by the object lens, is inverted at c, which is the focus of the eyeglass d, and through which the image is then seen, still inverted." -Comstock 1850

Refracting Telescope

"Suppose a, to be a distinct object, from which pencils of rays flow from every point toward the object…

"Suppose the object o to be at such a distance, that the rays of light from it pass in parallel lines, p, p, to the great reflector, r, r. this reflector being concave, the rays are converged by reflection, and cross each other at a, b which the image is inverted. The rays then pass to the small mirror, b, which being also concave, they are thrown back in nearly parallel lines, and having passed the aperture in the centre of the great mirror, fall on the plano-convex lens e." -Comstock 1850

Refracting Telescope

"Suppose the object o to be at such a distance, that the rays of light from it pass in parallel lines,…

"The spy-glass or terrestrial telescope avoids the inversion of the image by the interposition of two double-convex lenses, m and n, between the objective and eyepiece. The rays diverging from the inverted image at I cross between m and n, and form an erect magnified, virtual image at ab." — Avery, 1895

Terrestrial Telescope

"The spy-glass or terrestrial telescope avoids the inversion of the image by the interposition of two…

Zenith telescope constructed at the International Stations at Berlin by Hermann Wanschaff.

Zenith Telescope

Zenith telescope constructed at the International Stations at Berlin by Hermann Wanschaff.

"An instrument for the measurement of horizontal angles, consisting essentially of a telescope mounted so as to move on a pivot both horizontal and verticaly." — Williams, 1889

Theodolite

"An instrument for the measurement of horizontal angles, consisting essentially of a telescope mounted…

"One of the most important of astronomical instruments, consists of a telescope fixed to a horizontal axis, so as to revolve in the plane of the meridian, and is employed, as its name denotes, in the observation of the meridian transits of the heavenly bodies. The axis, which is the most important part of the instrument, and thus demands the utmost care in its construction, consists of a hollow sphere or cube, to opposite sides of which are tightly fastened the bases of two cones in whose apices the pivots are screwed; the sphere or cube is pierced for the admission of the telescope, which is firmly soldered at right angles to the axis." — Chambers, 1881

Transit Instrument

"One of the most important of astronomical instruments, consists of a telescope fixed to a horizontal…

"The instrument is supported on a strong tripod, fitted with levelling screws; to this tripod is fixed the azimuth circle and a long vertical steel axis. Fitting on this axis is a hollow axis which carries on its uper end a short transverse horizontal axis. This latter carries the telescope, which, supported at the center of its length, is free to rotate in a vertical plane. The telescope is thus mounted excentrically with respect to the vertical axis around which it revolves." — Encyclopedia Britannica, 1893

Zenith Telescope

"The instrument is supported on a strong tripod, fitted with levelling screws; to this tripod is fixed…