When a comparison is made of modern Chemical, physiological and industrial methods with those commonly practised only about a hundred years ago, it is quickly realised that without the expansion thermometers very little progress could have been made, temperature measurement and control having not only become essential features in practically every field of activity, but in a great many cases, having been the basis of the investigations, results of which are now seen wherever modern production methods are in use, or where the lessons of scientific research are being applied.
We must go back nearly 400 years, however, to find the first recorded account of an attempt to measure temperature, for until then, only visual or sensory evidence was used in its estimation – the bubbling of water when boiling point was reached, the formation of ice indicating freezing point; the change in the colour of the dough as bread was baked, and so on. Then in 1592, Galileo invented his air thermoscope, using the expansion and contraction of nearly all substances under the influence of heat and cold respectively as the basis of the appliance.
He used air as the expanding and contracting medium, and employed a glass-tube with a bulb at one end the other end being open. To prepare it for use, the open end was immersed in a vessel containing water and the bulb gently heated. The air in the tube expanded and some of it bubbled out through the water. The bulb was then allowed to cool and the consequent contraction of the air inside caused water to be drawn up into the tube. From then on, if the temperature of the air surrounding the bulb rose, the water would be driven down the tube, to rise again as the temperature fell.
It was not until some years later that any real form of temperature measurement was attempted when, in 1626, Sanctorious made a thermometer working on the same principle, having a tube with a number of bends to provide a greater length. This was fastened to a board on which a rough scale was inscribed and the apparatus is generally accepted as the first clinical thermometer, because its main object seems to have been to measure the heat of the body.
This, curiously enough, does not seem to have been connected with physiological research, but had as its object the establishment of a system of calibration in which the heat of the body was to be one reference point. Variations of atmospheric pressure affected the air-thermoscope adversely, and in 1654, Boyle, often described as the “Father of Chemistry”, improved on it by introducing hermetical sealing of the tube and using liquid (alcohol) as the expanding medium instead of air, the instrument reaching a form from which it was departed very little up to the present time.
During the latter part of the seventeenth century, research continued with the object of establishing a system of calibration which would enable comparative readings between thermometers to be taken.
As before, the heat of the body was taken as one reference point, but the desirability of other fixed points became apparent, and in 1694, one Renaldeni used the freezing and boiling points of water for this purpose, but these were not generally accepted until Fahrenheit established his scale in 1709. It is interesting to note, however, that the first scale made use of the freezing point of water and the bodys temperature as the reference points and had only twelve divisions. Later on these were sub-divided into eight, giving ninety-six divisions on the scale, the highest of which corresponded approximately to the recognised normal body temperature to-day.
Fahrenheit is also considered to be responsible for the introduction of mercury as a filling, so that by the early years of the eighteen century, the direct reading expansion thermometer had been evolved in a form differing very little in general design from that in common use today.
With such means of temperature measurement becoming available to chemists, physicists, physiologists and others, it was natural that investigation into the application of the thermometer in wider fields should take place. The early experiments, using body heat as a reference point, had shown that a relation existed between a persons temperature and his or her general state of health, but it was not until the middle of the nineteenth century that Wunderlich, after some years of studying the problem, published, in 1868, a treatise setting forth the results of his research and it is generally considered that the use of a clinical thermometer became an established part of the medical routine after its appearance.
The clinical thermometer of those days was very different from the small, handy and easily read type familiar to readers of this article. They took the form of engraved stem instruments, sometimes up to about 12″ in. long, with a range of 90* to 110* F., each degree being sub-divided into 1/5* F., a scale so open that reading must have been very difficult.
Apart from this, readings had to be taken with the thermometer in position as no maximum registering device was incorporated, and where the temperature under the armpit was required, a bent thermometer was used. The medical practitioner of those days was consequently burdened with a large wooden case containing a set of two thermometers, one straight and one bent, to do the work achieved by the small 4″ in. instrument with which we are familiar.
Prior to Wunderlichs researches, however, scientific working in other fields had devised means of registering the maximum temperature attained, such as the metal cored glass index as used in the Sixes maximum and minimum thermometer (invented by James Six of Colchester in 1782), and much later the separated mercury column type of index known as the Philips maximum index, invented by a professor of the University of Oxford of that name just prior to the Great Exhibition of 1851, the adoption of which to clinical thermometers took place some years later.
In the meantime, Luigi Peroni, a glass-blower of Hatton Garden, London, invented the lens front, by means of which the thin column of mercury in an open scale thermometer could be magnified considerably to facilitate reading, and this, together with the constricted bore tube in which the whole of the mercury column remains at the highest temperature reached until shaken down, remains the last important development in clinical thermometers.
Parallel with the increasing use of the thermometer by physiologists were the extensive applications being made in other branches of science. Once it was realised that the thermometer was the key to almost illimitable fields of research, physicists and chemists began to demand more and more special types of thermometer suited to the particular problems they were investigating, and as a result of growing interest in temperature measurement and control among the industrialists still further patterns were produced.
In the same way, more scientific methods of food production, farming, and domestic industries generally, emphasised still further the extent to which those improved methods relied on accurate thermometers, and by the later years of the nineteenth century the demand for thermometers had reached significant proportions.
It was about this time, in 1888 to be exact, that the late Giles Henry Zeal established himself as a thermometer maker, specialising in the production of high-grade clinical thermometers, in Turnmill Street, off Farringdon Road, London, already known as the district in which skilled glass-blowers were to be found.
With a force of about twelve skilled journeymen, he commenced operations and prospered. In 1902 his elder son, Henry Herbert Zeal came into the business, which continued to expand, and in 1921 was turned into a private limited company with G.H. Zeal as managing director, the other directors being H.H. Zeal and his younger brother, Raymond Oakley Zeal who had joined the firm in 1920.
In 1922 the continued growth of the undertaking demanded larger premises, and these were found in St. John Street, Clerkenwell, where the concern remained for some twelve years during which time a system of production had been established which catered for a far wider variety of instruments than had at first been contemplated, and that side of the business which specialised in industrial thermometers had achieved a system that might be described as approaching mass production, but retaining as essential features those processes which ensure that each instrument is treated individually at the importance stages of its construction.
As indicated above, by 1934, the St. John Street premises failed to provide adequate accommodation for the staff, which had increased to 280, and a modern ground floor factory was built at Lombard Road, off Morden Road, Merton, to which the business was duly transferred on completion.
In 1935, the firm of W. Reeves & Co., specialists in brewers instruments, was acquired and a new company, W. Reeves & Co., Ltd., was formed to continue the business which had been carried on for a number of years and had a high reputation in the industry for which it catered.
