Jason Clarke Antiques

Art Deco Dragoyle Air Tester by John Swain & Son Ltd


For sale, a scarce and very complete example of an early Twentieth Century Dragoyle Air Tester, retailed by John Swain & Son Limited of 89-92 Shoe Lane, London.

It needs little more introduction than the quote from Dr EE Slosson Director of Science Service, Washington DC.

“The Dragoyle works to a charm. The only fault I have to find with it is that it is such a fascinating creature that I waste my time watching its manoeuvres when I should be working. Also, it attracts the attention of my visitors and distracts their attention from me, because they all want to know what it is for and how it works”

The following transcript forms part of the original marketing documentation for this super Art Deco period novelty. Dr Slosson’s personal insecurities aside, the Dragoyle was given serious consideration in a 1926 article of The Analyst and although it was given merit, it was not considered “an instrument of precision”. Nevertheless, a rare, interesting and somewhat bizarre attempt to productise meterology instruments. I adore it!

THE AIR-TESTER (British Patent No: 230617/24)

The barometer measures the pressure of air. The thermometer measures the temperature of the air.  The AIR-TESTER measures the rate of evaporation of the air.

The evaporating power of the air depends on two factors, humidity and air motion or circulation. Thus the air tester measures the first two of the three factors of “air comfort” which are, humidity, air circulation and temperature.

Elaborate scientific study over the last ten years has shown that all these three factors really matter to the ordinary person indoors, for comfort and efficient work and for the first time in history we have an instrument, which is both simple and fascinating, that takes account of two of the three factors, whose importance most house-dwellers, in this age of science and reason, will appreciate.

The Air-Tester used in conjunction with an ordinary thermometer will correctly indicate how the best working conditions in factories, workshops, offices or rooms may be obtained.

The comfort and efficiency of an ordinary person depends to a large extent on the atmosphere in which he lives, and to those who live sedentary lives such as workers in factories or offices, in fact to all those whose avocations call for a large part of indoor life, this invention particularly applies.

The temperature of a room can be regulated by the ordinary thermometer but only to the extent of taking account of cold and heat; there are however two other essential atmospheric factors affecting health which are lost sight of in nine cases out of ten, owing to there being no simple yet adequate test by which to check them.

These two factors may be referred to as humidity and air motion, and in hot rooms, especially when many are working together, these factors are of more importance than the actual temperature. Now the Air-Tester takes account of both of these, because it measures the rate of evaporation of water.

In a crowded room the temperature is steadily raised by the body heat of the occupants, whilst the moisture content of the air is also steadily increased by respiration.

Before the Air-Tester slows below the minimum value for the room temperature, you should either introduce the “Air Motion” factor of comfort by means of a draught, artificial or natural, or lower the temperature by letting in cooler air, if this can be done; or do both.

To read the signal of the Air-Tester, count how many strokes it makes per minute; the greater the evaporation the faster it goes; it is not necessary to count a whole minute, for example, count half a minute and double what you get. (See table in images provide).

Tester, movement 15 strokes per minute (the normal as per table should be 24), probably indicates that an increased air circulation or lower temperature is required, or both.

Or again; room temperature 68F, and Air-Tester is going 45 to the minute; the person responsible for your heating may not believe it, but your room is too cold, you should therefore if possible reduce draughts, or add moisture to the air, or, as a last resource use the less desirable plan of raising the temperature; any one of these different methods will serve to raise the “effective” temperature of your room to a point within the comfort zone, but the last, repeated too often, may cause irritation of the skin, or the membranes of your throat and nose.

The Air-Tester requires attention once a week rinse the head and tube in cold water and refill the body container.

Perpetual motion? Very nearly, but not quite; perhaps as near to it as we are ever likely to come. Besides being of direct usefulness in giving an unprejudiced and impersonal estimate of the fitness of your room atmosphere, the Air-Tester has been said to be the most interesting scientific device since the Radiometer of Sir William Crookes in 1875, moreover the Radiometer stops working when the sun is not shining, whilst the Air-Tester will usually go for a week on one single filling of water.

The thermometer is an instrument of great utility, but is of little use as a comfort meter, because until recent years it was not clearly understood that there were two other factors in addition to the temperature factor, that govern the comfort and healthiness of air conditions namely, humidity and air motion. Here are some simple experiments to give you familiarity with the instrument, try fanning the Air-Tester and see how readily it responds to air movement. Breathe your moist warm breathe very close over its head and watch it faint into inaction. Set it on the inside sill of a closed window in winter, and see by its increased activity in spite of chilling, how strong a downdraught of cold air falls from the window pane. Cover the Air-Tester with any glass vessel wetted inside, although the temperature does not rise, yet the increase of humidity will finally make the Air-Tester cease to function.

The water container represents a Dragoyle, one of the dragon family closely related to the Gargoyles which as the world knows , spout liquid from their mouths; so our dragoyle behaves just as all dragoyles should.

The Air-Tester is a product of Great Britain invented by a Scottish professor of chemistry; it was originally made in America where the sales since the commencement of the year 1925, when it was first put on the market have been phenomenal; the manufacturers have been inundated by enquiries from Scientific Societies and the general Public throughout the United States for particulars of the invention. The Air-Testers sold in Great Britain are marketed under special licence from the inventor.

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