206 SEXTANTSolmon Marks and Co, Cardiff
20 radius
Brass sextant with wooden handle and finely engraved silver scale. The mirrors and filters are present but the telescope is missing.
206 SEXTANT
Solmon Marks and Co, Cardiff
20 radius
Brass sextant with wooden handle and finely engraved silver scale. The mirrors and filters are present but the telescope is missing.
Light from a celestial body such as the Sun or a star is reflected by a mirror attached to a moveable arm, through a mirror which also allows the horizon to be sighted simultaneously.
By bringing the image into coincidence with the visible horizon it is possible to measure the elevation of the body. Using an almanac and an accurate clock it is then possible to determine the position of the observer on the Earth's surface. This was the standard method of navigation from about 1800 until about 1980.
References:
N.H.
59 BUBBLE SEXTANT MARK IXA
A.M. Bubble Sextant Mark IXA Ref. No. 6B/218, Ser.No. 10651/42(v)
20*14*15
Black japanned metal case with rubber rimmed eyepiece at back and open slot at front where a black drum houses the clockwork automatic averaging attachment. The left half of the sextant carries the bubble and its collimating system, which together form the artificial horizon, while the right half carries the sextant proper: the mirrors and filters and angle scales. Lamps are provided for night observations.
A normal sextant is unsuitable for use in an aircraft because the horizon is not level with the observer as in a ship, so the bubble sextant was developed for aeronautical use in the 1920s.It was very important in WWII. The automatic averaging atachment was meant to ensure that unbiassed measurements were made while the bubble and observer wobbled randomly, so that the error would reduce as the square root of the number of observations. Sixty measurements were averaged as the observer tried to keep the bubble and a star in coincidence for a two minute period.
References:
image a image b image c image d image e
N.H.
064 SPHEROMETER
8*5D
A circular steel rim, 5 cm wide and 1 cm high, with three identical spike-shaped legs at equal 120° angles, beneath. A central support with inset screw thread, forming a similar spike of variable height. A rotating disk fixed horizontally to the circular rim, with gradations to measure the height of the disk.
Used to measure the radius of curvature of an extended object, for example a lens, to reasonable precision. The vertical scale is used as a height measurement for the screw (with the disk as a marker), and the graduations on the disk as a fine-resolution device for the same measurement, to fractions of a revolution. Adjustment of the screw to place all four legs on the surface, allows calculation of the radius of curvature from the height measurement and the dimensions of the device.
S.G.
171 ASHDOWN ROTOSCOPE
A.J.Ashdown Ltd., London
16*14*18
A patented shutter controlled by a gear connected to a centrifugal governor. A winding rod fits under the bottom handle to wind a spring. The speed of the gear is controlled by 5 sliding gear -coarse settings and an infinite graduation control achieved by a balanced centrifugal governor.
The Ashdown Rotoscope acts to gear human vision up to zero speed relative to an object having recurrent motion. A shutter turns at an accurate speed only allowing the viewer to see at instants certain time intervals apart. If the object under test executed a recurrent motion, then it is possible to view the object as stationary, or nearly so, by adjusting the time interval accordingly. The governor can be made to run between 50 and 125 RPM and thus by multiplying this with the gear ratio, the shutter speed may be calculated. The Rotoscope was used in two ways:
References:
M.C.
25 CHRONOMETER, ELECTRIC WIND
(Mercer' Repeater Contact Clock MS 152)
Thomas Mercer Ltd., St. Albans, England, (1956)
48*27*23
Wooden case contains electrically rewound chronometer with 1s contacts and repeater dial mounted on door. The repeater movement consists of an electromagnet which, when energised by a current impulse from the master clock, causes an armature to close and a pawl to advance a feed wheel one tooth. A train of gears from the feed wheel spindle drives the hands .
The master clock has a heavy balance wheel and helical balance spring and a spring detent chronometer escapement. Each second a pair of contacts closes and a current pulse is sent to the repeater movement. The driving spring is normally rewound at regular intervals by an electromagnet but can run for up to four hours if the supply is interrupted.
Such clocks were used to control dials in the public areas of ocean liners. This one was used for accurate timing of radio propagation experiments carried out at Mt. Nebo and Everton Park.
References:
N.H.
27 PENDULUM MASTER CLOCK
SYNCHRONOME ELECTRICAL COMPANY OF AUSTRALASIA, BRISBANE
126*27*14
Grey painted wooden case with glazed door. Lower dial with hour and minute hands and seconds bit and. upper dial with sweep seconds hand only mounted on inside of door. Black japanned casting carries pendulum, countwheel, gravity arm and solenoids.. Subsidiary seconds counter fitted.
Electrically reset gravity escapement. With each swing of the seconds pendulum, the countwheel is advanced one tooth. Each half minute, a detent is tripped and an L-shaped lever falls down. It carries a roller which impulses a specially shaped arm attached to the pendulum, keeping it in motion. The other arm of the lever makes a contact which energises the solenoids . These pull in an armature which resets the lever ready for the next half-minute impulse. The same current also flows to the solenoids operating the dial(s). As this moves the hands only twice a minute, a subsidiary seconds counter, which provides an impulse at each swing of the pendulum, has been fitted to this clock which was used to time and control ionospheric observations at the Moggil field station, starting in the International Geophysical Year in 1958.
Synchronome pendulum clocks were also widely used in the University to operate slave dials in lecture rooms and to control bells and timers.
References:
N.H.
124 SUBSTANDARD METRE (c 1910)
Made by the Societe Genevoise, Geneva for the Cambridge Scientific Instrument Co
176 Invar Coulee 1833 No 12214
105*2.5*2.5
The Invar substandard metre is contained within its own box and has a cross-section which looks like: H The bar is marked off in millimetres, with every tenth one enumerated. The last (1000th) millimetre has ten fine subdivisions. A travelling microscope would have been used to make measurements with the substandard metre. Preserved in each country was a standard metre against which the substandards were compared.
Invar is a nickel-steel alloy (35.6% nickel) with an extremely low coefficient of thermal expansion. It was invented in 1890 by the Swiss Charles-Edouard Guillaume (1861-1938) whilst working for the International Bureau of Weights and measures in Paris. Guillaume received the Nobel Prize for Physics in 1920 for his work with nickel-steel alloys.
The metric system came into being in France in the 1790s. The metre was originally defined as 10-7 of the Earth's quadrant (passing through Paris) and the first standards were platinum. During the nineteenth century, the metric system was gradually embraced by nations world-wide. In 1960 the metre was redefined in terms of the wavelength of the orange-red line in the krypton-86 spectrum and more recently as the distance travelled by light in vacuum in a certain number of oscillations of a Cs clock.
References:
J.C.
30 McLEOD GAUGE
W. Edwards & Co. Ltd., London
Lacquered wooden upright stand supporting vacuum tubes and compression bulb. Mounted below the assembly, a moveable metal weight, acting as a plunger. The McLeod gauge is a form of mercury manometer adapted for the measurement of pressures in the 1 - 10-3 Torr range.
To make a pressure measurement, the weight is lowered emptying the compression bulb. Connecting the vacuum system to the gauge, the weight is then raised filling the compression bulb with mercury, first trapping the gas contained within it and compressing in into the capillary tube. This effectively amplifies the system pressure. Knowledge of the bulb volume and capillary diameter allows a direct calibration.
References:
A.H.
294 MERCURY FORTIN BAROMETER
Griffin, London 2195 (c1920)
A wooden wall plaque supports a brass outer casing which protects the glass barometer tube and wood and leather cistern. A brass screw provides the means to raise or lower the level of mercury in the cistern to a fiducial point in the form of an ivory pointer. Air pressure on the free surface of the mercury in the cistern supports the column of mercury, the length of which is read by a vernier operated by a rack and pinion over a graduated scale marked on the casing. A mercury thermometer attached to the casing gives the temperature of the barometer, and allows corrections to be made.
The Fortin Barometer was commonly used at meteorological stations to measure atmospheric pressure. The advantages of this type of barometer are its portability (inverted), and that it permits the inspection of both free surfaces of mercury whose difference in level have to be measured. The major disadvantage is the cistern and the mercury it contains require frequent cleaning to maintain the instrument's accuracy. This particular Fortin Barometer was in use in the second year laboratory until 1994. Restored recently, it would still be operational, however it contains no mercury.
References:
A.B.
055 5061A CESIUM BEAM FREQUENCY STANDARD (c1970)
Hewlett Packard. Ser. No. 92400331
58*42*22 cm
Rectangular grey metal casing, front panel consisting of analog time display and three output frequencies, with a pop-down insert panel containing advanced display and adjustment controls.
It uses a beam of state-selected Cs133 atoms subject to microwave induced transitions in their hyperfine energy levels. Atoms prey to transitions are detected by an electron multiplier, the current in which contains a frequency component used to correct the frequency of a quartz oscillator. Provides standards of 5MHz, 1MHz and 100khz.
Similar frequency standards were flown around the world in commercial airlines to prove experimentally relativity theory. Relativity (special) predicts that clocks that stay at home will read a longer time than ones which travel, although in the context of flying around in a plane, the time difference is of the order of 40 to 275 nanoseconds. The Cesium clock keeps time with accuracy of one part in 10^11 and thus is adequate for such experiments. This particular clock was used in experiments with ULF waves for the Omega Global Navigation System (a Navigation system for submarines using ULF waves to triangulate position). ULF waves are affected by the ionosphere, and such a frequency standard is needed to determine its effects.
References:
S.H.
056 RUBIDIUM FREQUENCY STANDARD MODEL 304-B (c1970)
General Technology Corporation, USA
13*42*48
Instrument provides standard frequency outputs of 5 MHz, 1 MHz and 100 kHz, via BNC terminals mounted on the front panel.
A vapour of Rubidium contained within a small glass cell has an unvarying absorption frequency fo of approximately 6834.68 MHz. The crystal oscillator within the device nominally operates at a frequency f, an integral submultiple of fo. An error signal proportional to the difference (f-fo) is developed and applied to the oscillator, such that the difference is reduced toward zero. In this way, the stability of the Rubidium frequency is transferred to the oscillator, whose signal is translated into the standard output frequencies. The device provides a quoted long term stability of 1 part in 1010.
This particular instrument was used by the late Dr. J. Crouchley, formerly of the department's ionospheric group, in VLF monitoring experiments.
Reference: Operating Instructions. Model 304-B. Rubidium Frequency Standard. General Technology Corporation, Torrance, California (undated).
WB
123 ELECTRICALLY DRIVEN TUNING FORK
Maker unknown
67*21*26
Mounted on a base of timber, with a glass fronted wooden cover, is a steel assembly holding the tuning fork and two movable electromagnets, one between the two prongs at the end of the fork, and the other closer to the fork base with coils on either side of the lower prong.
This device was used to maintain the vibration of the tuning fork for long periods of time, in experiments where a constant and well defined pitch was required, e.g. Doppler effect. Essentially, the apparatus functions by attaching a battery across one of the fork prongs. The current thus produced, causes the electromagnet to do work on the prong when it is moving away. The circuit is broken when the prong is moving back towards the magnet so that this advantage is not lost. This interrupted current is usually achieved by using a rigid wire contact between the prong and one terminal of the voltage source.
References: Poynting & Thomson, SOUND, Charles Griffin & Co., London, 1900, pg.42.
AR
POCKET SUNDIAL
Small floating dial in wooden case on loan to museum. Southern hemisphere dial apparently marked out for the lattitude of Melbourne,
and exhibiting about 8 degrees of magnetic deviation, also appropriate for that location.
POCKET SUNDIAL
Small floating dial in a brass case. Incomplete.
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