1851 Great Exhibition: Official Catalogue: Class X.: William Simms
741. SIMMS, WILLIAM (surviving partner in the firm of TROUGHTON and SIMMS), 138, Fleet Street — Inventor and Manufacturer.
An equatorial instrument, adapted for the latitude of 25°, and mounted generally after the method of Frauenhofer; it is furnished with a clock-work motion, so that the telescope moves so as to counteract the effect of the earth's rotation; the diameter of the object-glass is four inches and nine-tenths of an inch, and its focal length is about 7 feet.
The declination axis is open and exposed between its two supports; its ends are cylindrical, and admit of the application of a spirit-level, by this means the adjustment of the instrument is facilitated, and it is readily brought to the meridian, and thus, observations of transits over the meridian can be made sufficiently near for identifying an object.
The illumination of the telescope is regulated by the application of the throttle valve of a steam-engine, and is as effective as the more elaborate methods hitherto in use.
A best spider line position micrometer, of which extensive use has been made in measurements of the relative position and distance of binary stars. The position circle is divided to one minute of arc, and the reading is by means of opposite verniers upon the edge of the circular plate to which the micrometer is fixed; the value of the micrometrical divisions, however, depend on the focal length of the telescope with which this instrument is employed.
An annular micrometer, and a set of negative eye-pieces are shown with this instrument.
An equatorial instrument adapted for the latitude of London, on the same principle as the preceding, but without clock motion. It has been arranged as an inexpensive, but at the same time an effective instrument. The diameter of the object-glass is 3 ± inches, and its focal length is about 45 inches; it is provided with a spider line position micrometer of the second order, in which one screw motion only is given.
The whole is supported upon an iron column with suitable arrangements for its final adjustments.
[An equatorial instrument consists of a telescope fixed to a graduated circle called the declination circle, and of a polar axis, to which is fixed a circle called the hour circle. When the instrument is adjusted the polar axis is parallel to the axis of the earth, and perpendicular to the plane of the hour circle, and to the axis of the declination circle, etc. In its use, the delination circle can be turned about the polar axis, and the telescope can be directed so as to be inclined at all angles to the earth's axis, and by the means of these two motions, the telescope can be directed to any point iu the heavens, and if a clock-work motion be applied, an object when viewed through the telescope seems to be without motion, affording the opportunity of examining it minutely.—J. G.]
The altitude and azimuth instrument known as the "Westbury Circle," so called from the valuable observations made with it at Westbury by John Pond, Esq., the late Astronomer Royal, by which a change of figure in the great mural quadrant at the Royal Observatory was clearly demonstrated.
This instrument was made originally by the late E. Troughton, and subsequently repaired and re-divided by the exhibitor. The re-division was effected by the process invented by Troughton, and described by him in the Philosophical Transactions for 1809.
The diameter of the altitude circle is 30 inches, and of the azimuth 24 inches. The spaces upon the respective circles measure five minutes of arc, which are subdivided to single seconds by two opposite micrometer microscopes. Five revolutions of the micrometer screw being, by the optical arrangement, made to measure five minutes of arc upon the circle; the 60th part of a revolution of the micrometer screw is, therefore, equal to one second of arc. The positions of the azimuthal micrometers are unalterable; those of the altitude circle are fixed to the extremities of an arm which is moveable upon a centre, an arrangement which admits of their positions being altered relatively to the zero of the circle, and hence the readings obtained upon particular objects are changed in every new series of observations. Such errors as are due to the graduation are by these means much diminished if not entirely eliminated. The axes are adjusted by means of spirit levels, in addition to which, the instrument is furnished with a plumb-line apparatus.
A portable altitude and azimuth instrument, each circle is 15 inches in diameter, graduated upon bands of silver to five minutes of arc, upon Mr. Simms' new self-acting dividing engine. There are two micrometer microscopes to each circle showing single seconds of arc. The microscopes have achromatic object-glasses. This instrument is furnished with the nadir point apparatus, or central collimator, the invention of the exhibitor, which consists of a telescope in the interior azimuthal axis, around which the superior parts of the instrument revolve. The spider lines, in the form of an acute cross upon the diaphragm of this central collimator, being placed in the principal forms of its object-glass, can be seen in the telescope of the instrument when it is directed downwards, or towards the Nadir; and their intersecting point serves as an object to which every observation made with the instrument can be referred, and therefore supersedes the use of an artificial horizon, or other extraneous means having the same object in view. The transit collimation can also be adjusted by its means, without reference to any external object, and it supplies the place of the riding level for the transit axis, in the event of its being broken.
[If the polar axis of an equatorial instrument, instead of being inclined so as to be parallel to the axis of the earth, be vertical, it becomes an altitude and azimuth instrument, the hour circle becoming the azimuth circle, and the declination circle becoming the altitude circle, and is capable of determining the altitudes and azimuths of any celestial objects.—J. G.]
A transit circle, 2 feet diameter, with two reading micrometer microscopes having achromatic object-glasses; the divisions upon the circle are sub-divided to single seconds by the micrometers. This circle was also graduated upon the self-acting dividing engine invented by the exhibitor, as were also the circles of the altazimuth and the transit circle lately made for the Royal Observatory at Greenwich.
The telescope is achromatic and has an aperture of 3.25 inches, and a focal length of about 46 inches. The apparatus by which the field of view is illuminated is the invention of the exhibitor, and has been adapted to the great transit circle at the Royal Observatory. The field of view and the wires interchange the conditions of light and darkness; hence, if the object be a bright one the field of view can be illuminated, and the wires appear as dark lines upon it; but if the object be a faint one, the field can be made dark, and the wires luminous. This change is brought about instantaneously by either drawing outward or pressing inward a small cylindrical plug placed conveniently for the observer.
The illumination of, the divisions upon the circle is effected by the same lamp which illuminates the field of the telescope, as follows:-
A prism adjoining the microscope object-glass, receives the light from a lens in the side of the lantern, which is condensed upon the graduated face of the circle as a disc of light, which just covers the extent of the field of the micrometer microscope, and is so arranged that a normal to the face of the circle, bisects the angle formed by the incident and reflected rays.
The instrument is supported upon wooden models of the stone piers upon which it will be ultimately fixed; and the whole may be taken as a representative of the class of instrument which is now rising in the estimation of British astronomers.
A transit instrument 3.5 feet focal length, and 2.75 inches aperture, with two setting circles upon the telescope tube, axis level, micrometer in the eye piece, etc., as is usual in the most perfect instruments of this class; but as this instrument has been made for the coast survey of the United States, now being carried on under the direction of Professor A. D. Bache, and is intended for observations both in the meridian and prime vertical, the exhibitor has introduced two additional parts to fit it the better for its work. Firstly, a reversing frame by which the telescope can be lifted from the Y's, turned end for end and again lowered into its bearings without being subjected to any handling, or other operation by which the parts may be unequally expanded and the adjustments deranged; the operation is safe and expeditious. Secondly, both the pivots are perforated, in one of whi9h a diaphragm with cross lines and an eye piece is fitted, and in the other an object-glass of suitable focal length is fixed, and hence the axis becomes a telescope. Now, if this telescope be directed to any object, such as the cross lines of a collimator or any terrestrial mark that presents itself, or is set up at a considerable distance from the instrument, and the axis be made to revolve, the form of the pivots may be thereby examined, or (which in the instrument exhibited, is its primary purpose) this telescope may be used for turning the principal telescope 90°; that is to say, for changing its meridional to a prime vertical position, or the reverse.
This instrument is supported upon a cast-iron stand.
[The transit instrument consists of a telescope placed in the meridian. It is fixed to two arms, the extremities of which are turned into two equal cylindrical pivots, which turn in Y's on the top of two piers, placed east and west of the centre of the telescope. The centres of the pivots, or their axes are in the same straight line, which is called the axis of the instrument. In order to observe the instant that a celestial object passes the meridian, there is placed in the telescope, at the focus of the object glass, a system of fine cobweb wires perpendicular to the horizon, and one placed horizontal. At the instant an observation is made, the star's image coincides with the intersection of these wires. An arrangement of this kind is absolutely necessary, as the field of view of the telescope is not a mere point.
The transit instrument is used in connexion with an astronomical clock, adjusted to sidereal time. A clock so adjusted that it completes a circuit in a sidereal day, and indicates Oh. Om. Os., when the first point of Aries is on the meridian, and having its dial-plate divided into 24 equal spaces; hence, when the transit instrument is adjusted, and the clock goes correctly, at the instant the first point of Aries is on the meridian, the time shown by the clock is Oh.; when this point is 15° or 30° west of the meridian, the time shown by the clock is 1h. or 2h. respectively, and so on. As the angular distance from the first point of Aries thus measured, is called right ascension, the right ascension of all stars, etc., are thus determined.—J. G.]
A diagonal transit instrument, in which the means of illuminating the field of view is new in this class of instrument, and is the invention of the exhibitor.
The mode hitherto adopted has been the placing of a reflecting surface in front of the object-glass, and receiving light upon this plate from a lamp or candle placed in a distant part of the observatory. The objections to this mode are, the difficulty of throwing light upon the reflector at all, under such circumstances; besides, for every observation, a new arrangement of the light has to be made; and further, by the reflector being placed in front of the object-glass, part of its light is cut off.
In the instrument exhibited, the light passes through the axis, and this is effected by placing a lens, of which a very large segment, nearly an annulus, projects beyond the edge of the diagonal reflector within the axis. The light, passing through a small lens fixed in one of the pivots in the usual way, diverges upon the open segment of the interior lens, and is thereby converged to the opposite pivot, where the diaphragm is placed.
An isometrical elliptograph invented by the Astronomer Royal, G. B. Airy, Esq., by which ellipses in isometrical perspective can be drawn with great facility and accuracy. The exhibitor is the manufacturer.
Three imperial standard yards, made for Her Majesty's Commissioners for the restoration of the Standard of Weights and Measures, with the supports invented by Professor Miller and the Rev. R. Sheepshanks.
The bars, which are one inch square, are an alloy of copper with tin and zinc, the proportions of each constituent is engraved upon the bar, and these proportions were determined by the late F. Baily, Esq., after very careful experiments.
The planes upon which the divisions are cut, showing the standard yard, are at the bottom of cylindrical holes, and in the neutral axis of the bar. The divisions are upon pins of gold, and their situation is well calculated to defend them from everything but wilful injury.
Professor Miller's support consists of a system of levers by which an equal degree of support is given to eight equi-distant points in the bar.
Mr. Sheepshanks' support is simply a trough of mercury in which the bar floats, and is prevented from turning over by means of a stirrup in the middle of its length, with pivots resting in two Y bearings. To this apparatus is added two of Mr. Sheepshanks' recently made thermometers.
A 5-feet standard bar, and the 5-feet tubular scale, No. 4, of the late F. Baily's Report, are the property of the exhibitor, and have been used in the formation and comparison of many existing standard scales, both for this and for foreign countries.
A Troughton's reflecting circle, of the usual kind, the circle being cast in one piece. This circle was arranged as an improvement to that by Borda, and substitutes the reading of six verniers in a complete observation, for the repetition of the angle as practised with the older instrument.
A Troughton's sextant, having the advantage of lightness and strength in its construction.
A transit theodolite in which the ordinary vertical arc is extended to a complete circle, and is read by opposite verniers. The range of the telescope is unlimited, like that of a transit instrument, and by means of a diagonal eye-piece observations can be made even in the zenith.
The axis of the telescope is perforated, and the field is illuminated by a lamp attached to one of the supports, it is in fact, an altitude and azimuth instrument equally well-adapted for the surveyor and the scientific traveller.
Five achromatic object-glasses, one of 9 inches, two of 8 inches, one of 6191 inches, and one of 4 inches, effective aperture, all worked by the exhibitor. The discs of glass in the first-mentioned being of English manufacture.
[A telescope furnished with an achromatic object glass is termed an achromatic telescope. The distance of the point from the object-glass, where the image of an object is formed, is called the focal length of the telescope. The magnifying power of a telescope depends upon the following considerations, —if it be directed to the sun or moon, and a piece of transparent paper be held in its focus, an image of the object will be formed upon the paper. Now the size of an object depends upon the angle under which it is seen, and the image formed upon the paper will subtend exactly the same angle when moved to that distance from the eye which is equal to the focal length of the telescope, as the object itself, when viewed with the naked eye, or in other words, if held at such a distance from the eye as the focal length of the telescope, it will exactly cover the object itself. Suppose this distance be seven feet, we can with unobstructed vision view an object at the distance of six inches; if then we view the image at this distance it will appear fourteen times larger than the object it represents. By the application of another lens near the eye, termed the eye-glass, the image can be seen distinctly at a very much less distance, in fact, it can be viewed at the distance which is equal to the focal length of the eye-glass; and suppose this to be half-an-inch, then the image will appear twelve times larger than it did to the unassisted eye, and, therefore, fourteen multiplied by twelve, or one hundred and sixty- eight, would be the magnifying power of the telescope. Hence the rule for finding the magnifying power of a telescope, is to divide the focal length of the object-glass by the focal length of the eye-glass, and the quotient will give the magnifying power.— J. G.]