The King George III Collection

Although inexpensive and simple, Demainbray's apparatus tells us about the kind of science which interested him and his audience. Demainbray's early career has much in common with those of his rivals so his life throws some light on the business of philosophical lecturing to the wider public in the mid-eighteenth century. Demainbray's lecture apparatus now forms part of the King George III collection. Some of the items brought back from his travels across Europe were made especially for him.

 

Model of a pile-driver driven by a paddle wheel, 1754 In Lyons in 1754, this model was given to Demainbray by the Marquis de Grollier, who had inherited an unusual collection of clocks, machines and object d'art. The machines were built in the second half of the 17th century by Baron Nicolas Grollier de Serviere. The Baron had a pile-driver constructed on his estate which was operated by a water wheel held between two boats, although in the model it is attached at one side of a floating structure. It is a very simple device which probably delivered little power. © Science Museum/Science & Society Picture Library

 

Model of Valoué's pile-driver, before 1753 The pile-driver which was invented by James Valoué, a watchmaker, in about 1737, and used in the construction of Westminster Bridge in 1738, was described by Demainbray as 'the best of that kind that perhaps was ever seen'. This model was used by Demainbray in his lecture on compound engines, but unlike a later version given to him by the Marquis de Grollier, it required the use of horses. © Science Museum/Science & Society Picture Library

 

Inclined plane, before 1753 In the surviving syllabuses the inclined plane demonstration formed part of Demainbray's lecture on mechanics, which also included the wedge and the screw. This was a standard item in a course of experimental philosophy by the mid-eighteenth century. © Science Museum/Science & Society Picture Library

 

Model experimental cart, before 1753 This cart was identified from a sketch in Chabrol's lecture notes and Demainbray used it on the inclined plane to compare the performance of large and small wheel diameters carrying various weights. He stressed the advantage of large wheels, and, according to the syllabuses, recommended the use of a cart rather than a sledge. © Science Museum/Science & Society Picture Library

 

Pyrometer by Henry Hindley, c.1750 Hindley was an expert instrument maker whom Demainbray met in York. This pyrometer, a device for showing the thermal expansion of different metals, was made by Hindley to a design either by himself or by Demainbray. A metal bar is placed along the base and heated by a row of lighted wicks in an oil bath. As the bar expands, it pushes an arm which turns the pointer on the dial at the top. This pyrometer is one of the pieces of Demainbray's apparatus that can be identified from notes made at Demainbray's lectures in Bordeaux by one Père Chabrol. © Science Museum/Science & Society Picture Library

 

Butcher's orrery, 1733 This large orrery was Demainbray's most impressive instrument. Signed by Butcher of Bedford, a provincial clockmaker, it was made for Lord Trevor, Baron of Bromham in 1733. An eight-day clock rotates the planets. The calendar ring is four and half feet in diameter and has painted metal figures for the signs of the zodiac. © Science Museum/Science & Society Picture Library

 

Model of a corn mill at Toulouse, c.1753 Demainbray acquired several fine models on his travels through France. This one is of a corn mill on the river Garonne at Toulouse. The water was directed through a narrow channel on to a paddle wheel. The paddle was connected to a shaft which turned the upper grinding wheel. Demainbray later claimed that the model of this mill was 'the only one brought to England'. © Science Museum/Science & Society Picture Library

 

Diving bell models, c.1750 Two of Demainbray's four model diving bells have survived. 'The art of living under water' was an important part of Demainbray's course: salvaging goods from shipwrecks was a lucrative business. The glass bell was sunk using lead weights. A bird was placed in a wire cage which fits inside the bell; onlookers were able to see what happened when the air was used up. The tinplate diving bell is more sophisticated. It has a stopcock at the top to let out the old air and a lens to let light in. New air from barrels was introduced through pipes. © Science Museum/Science & Society Picture Library

 

Model of Dubost's mill, c.1753 In the 1740s a Frenchman called Dubost suggested a novel design for a corn mill for use on the Rhône. The mill was mounted in a boat, and could be moved to allow other traffic to travel up the river. The millstone was driven by an Archimedes' screw in the water. Demainbray seems to have had the model made when he visited Lyon in 1753. © Science Museum/Science & Society Picture Library

 

Model of Savery's engine, before 1754 Savery patented his "fire engine" or atmospheric engine in 1698 and presented it to the Royal Society the following year. Although it was a major technological breakthrough it did suffer considerable problems, the principal one being that the steam had to be held at very high pressures and temperatures which sometimes melted the solder and blew apart the boiler. According to Desaguliers "these discouragements stopped the progress and improvement of the Engine" making it useful only for raising water for gentlemen's seats and not in mines where the demand was greatest. Desaguliers and his colleagues studied the design of the early engines and made models and improvements. Demainbray used this model with the model Newcomen engine in his course on pneumatics. This model, but not the Newcomen model, was shown as a working demonstration, considerable attention being given to methods of preserving the boiler and repairing the cylinder as "being of utmost moment to persons concerned in Mines". © Science Museum/Science & Society Picture Library

 

Anamorphic pictures, c.1750. Anamorphic pictures using mirrors were fairly common in the eighteenth century. Demainbray used them, along with other optical toys, to open his course on optics. A cylindrical mirror is placed on top of a distorted picture. When viewed from above, the picture is instantly recognisable. Other distorted images viewed through the side of a conical mirror show sililar effects. © Science Museum/Science & Society Picture Library

 

Demainbray's microscope, c.1745 Demainbray demonstrated each of the main type of microscopes in his course. This microscope is engraved with Demainbray's name and is an example of a type known as a Scarlett's microscope after Benjamin Scarlett, the London instrument maker, who made the improvements that distinguish it from other designs. © Science Museum/Science & Society Picture Library

 

Demainbray's telescope, 1752 This telescope was bought by Demainbray from a maker in Bordeaux known only as Costa. He mentions the instrument in his syllabuses. It bears the handwritten signature 'Dr. Demainbray 1752'. It is unusual in that it has six lenses. © Science Museum/Science & Society Picture Library

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The Newcomen engine
The maximum engine