Lot 21

Louis Urban Jürgensen

Maximum Minimum

A rare index thermometer for measurements of the highest or lowest temperature at the same time with brass tripod in its original silk-lined morocco case

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The description of the "index thermometer" written by Louis Urban Jürgensen reads: "The thermometer is so constructed that the lowest degree of temperature at which the insrument has stood, together with that it indicates at the moment is seen at one and the same time. The scale is reaumur. To the instrument added a brass tripod upon which the former may be placed in such a horizontal position, as to admit the atmosphere in every dinestion. When the lowest degree or minimum is required, the knob of the external periphery of the case at 60° must be pressed in, the hand will then only be able to move back or towards the lower temperature....."
In 1834 Louis Urban created a new type of bimetallic thermometer. This thermometer could be set so that it indicated the highest or lowest temperature measured within an observation period at the same time as the current ambient temperature.
The indication of maximum or minimum temperature is indicated by a freely mounted additional hand which does not cause increased friction. The additional hand or index can be pushed by the main hand to indicate either the maximum or minimum temperature reached. This additional hand is made of gold and formed so that, as long as the main hand moves in the direction of the measurement required, it is almost completely hidden by the latter. The displacement is effected by a small pin placed a short distance from the centre, lying at the same height as the main hand. With the help of a setting pin, it is possible to position the index of the right of the main hand, if one wishes to find out the highest and vice versa on the left for the lowest temperature in a certain period. The silver case can therefore be opened from the dial side. Louis Urban also made several thermometers in which the main hands were in gold but the additional hand was in steel. In these thermometers a magnet was supplied for setting instead of an ebony setting pin.
Of course such instruments were not suitable for carrying in the pocket, even if they resembled an ordinary pocket watch from the outside. In order to obtain exact results, a quiet position surrounded by free air was required. For this purpose the instrument was provided with a gilded brass tripod, on which it could be placed upright.
As in the next step in the development of the bimetallic thermometer, it had of course to be equipped with two additional hands, so that maximum and minimum could be measured simultaneously.
After Urban Jürgensen's death, only few bimetallic thermometers were produced by Louis Urban, 11 pieces which had been commenced were completed and sold in the following year. Subsequently there were eight further pieces made. They all had silver or brass cases. In few of this low number of pieces, bimetallic thermometers made by the Jürgensen company must be considered very rare today.
Source: John M. R. Knudsen "The Jürgensen Dynasty", Kopenhagen 2013, pages 175ff.