Maker's Name: 
Where made: 
Where used: 
UQ research Labs
circa 1910
22 × 22 × 33 cm

This item is a radio-micrometer designed by Sir Charles Vernon Boys and produced by the Cambridge Scientific Instrument Company. A thermocouple and a single turn, low resistance coil are both suspended between the poles of a horseshoe magnet by a quartz suspension fibre. This thermocouple is made of bismuth and antimony. This device specialises in detecting infrared radiation, which we experience as radiated heat.

When infrared light is focused onto the thermocouple, the heating produces a slight electric current through the coil. This interacts with the permanent magnetic field of the horseshoe magnet and it begins to turn. The user can measure the slight rotation of the coil by observing the change in the position of the light reflected by the attached mirror.

In order to increase the sensitivity and accuracy of the radio-micrometer, Boys needed a thin, light fibre to use to suspend the thermocouple and mirror. He developed a unique method of creating thin strands of quartz that were less than 1 micron in diameter. To make these fibres, Boys fused one end of a piece of quartz to an arrow, and fixed the other. He then heated the quartz using a nitrous oxide flame, and fired the arrow from a crossbow. This flight stretched the quartz into the fine yet strong strands Boys used in his radio-micrometer. This new fibre allowed Boys to create a radio-micrometer that was capable of detecting, with the addition of a collecting mirror, the infrared radiation of a candle from three miles away. While Boys was also able to detect the heat from the Moon, he was never able to detect any infrared radiation from the stars or planets.

This item is part of the UQ Physics Museum ‘Before Photonics’ Tour
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N.R.H., J.D.B., S.N.