Professor Hugh Longbourne Callendar (1863-1930).
1885 At the Cavendish Laboratory - J. J. Thomson suggested he should tackle the accurate measurement of electrical resistance. Callendar's thesis on platinum thermometry was accepted, and he was elected a fellow of Trinity in 1886.
1899 Lord Rayleigh's committee on electrical standards accepted Callendar's proposals for a standard scale of temperature based on the platinum thermometer.
1900 Published an important paper, "Thermodynamic properties of gases and vapours deduced from a modified form of the Joule-Thomson equation" in which he represented the thermodynamic properties of steam by means of consistent thermodynamic formulae; this led to publication of the first Callendar Steam Tables in 1915. He also published The Properties of Steam (1920).
1925 Investigated dopes and detonation for the Air Ministry
1926 Published a report on the cause of knock in petrol engines and the effects of anti-knock additives in petrol.
1929/30 Obituary 
Hugh Longbourne Callendar was born in 1863 and was famous for his research work, much of which was carried out whilst a Professor at the Imperial College of Science in London.
His career as a teacher of Physics commenced at Cambridge in 1886 and was continued subsequently at Holloway College; McGill University, Montreal; University College, London; and finally at the Imperial College of Science, where for many years he was a distinguished member of the staff. His researches covered a wide field and are well known to all engineers, and among other distinctions conferred on him were a Fellowship of the Royal Society and the Watt Medal of the Institution of Civil Engineers.
He died on January 20th, 1930, following an operation.
He was elected an Associate of the Institution of Automobile Engineers in 1907 and an Honorary Member in 1919.
"THE LATE PROFESSOR H. L. CALLENDAR, F.R.S.
It is with very great regret that we have to announce the death of Professor H. L. Callendar, which occurred on Monday last, in a nursing home, as the sequel to an operation undergone some time earlier.
Born at Hatherop, Gios., in 1863, Hugh Long-bourne Callendar was educated first at Marlborough, on leaving which he proceeded to Trinity College, Cambridge, where he graduated in 1884-5, both in Classics and Mathematics, being, we believe, the last of a long line of eminent men who have taken a double first in both triposes. We have, however, heard him lament the time wasted on the Latin and Greek verse exercises, which then formed and, perhaps, still do, a necessary preparation for classical honours at Cambridge.
Callendar commenced what proved to be his principal life’s work, by selecting as the subject for a Fellowship dissertation, the experimental study of the specific heat of water, and, somewhat sanguinely, anticipated that he would be able to clear up all outstanding discrepancies with about a month’s work, but, it was, in fact, not till 1897 that, in conjunction with one of “ his greatest discoveries,” Dr. H. J, Barnes, that the difficulties were finally overcome, and the now accepted values determined. This work was carried through at the McGill University, Montreal, at which Callendar had occupied the Chair of Physics since 1893. The research in question was marked by one of Callendar’s outstanding characteristics as an experimentalist, namely, the evading of difficulties rather than the surmounting of them. Sir George Darwin, in comparing his own mathematical technique with that of Henri Poincar6, likened his individual methods to those of an amateur burglar who had to carry through his operations by the brutal expedient of “ safe blowing,” whilst Poincar6 neatly picked the mathematical lock. It was to the latter type of investigator that Callendar pre-eminently belonged.
Thus, whilst most of his predecessors, and not a few among his successors, employed calorimetric methods, which necessitated large corrections for the heat capacity of their apparatus, Callendar, by his invention of the continuous flow method, obviated entirely the need for such a correction, and reduced to a minimum that for radiation losses, by the expedient of enclosing the whole of the apparatus in a vacuum jacket. Moreover, by the invention of the platinum thermometer, which was made in connection with this research, he put in the hands of physicists the means of measuring temperatures with a precision and ease previously unprecedented. It was primarily in connection with this reseach that the E.M.F. of the Clark cell was determined in a joint study
by Callendar and Captain R. O.
King, now at the Air Ministry, but then working in the McGill Laboratories. It was with the platinum thermometer, too, that Dr. Barnes was able to measure the temperature of freezing water to the teoa of a degree Centigrade, and was thus able to show what extraordinarily small temperature differences were responsible for the formation of ground ice which, though seldom encountered in our climate, may be a source of much trouble and inconvenience to American and Canadian water supply and hydroelectric plants.
It was also with this instrument that Callendar and Coken made in the McGill Laboratories, some of the best observations yet recorded on the critical velocity of water in smooth pipes. The method was based on the fact that in stream line flow the rate of heat transfer between a tube and a through-flowing fluid is extremely small, but increases enormously with the setting in of turbulence. In the ultimate outcome, however, the most important application of the platinum thermometer was to the determination, in conjunction with the late Professor J. T. Nicolson, of the temperature of the steam expanding behind a piston. Possibly none of Callendar’s experiments have received more abundant, or less intelligent, criticism. It was, for example, asserted that it was impossible to measure accurately rapidly-varying temperatures. As a matter of fact, no attempt was made to do this, since it was the “ stationary ” temperatures at each end of the stroke, which were utilised in reducing the observations. Part of the objections made originated in the inherent dislike to have accepted convictions disturbed. Engineers had agreed very generally that the enormous discrepancy between calculation and observation met with in the analysis of the indicator diagram was entirely accounted for by initial condensation, a view which the research in question showed to he inconsistent with the facts. Here, as described in the paper, for which the Institution of Civil Engineers awarded a Watt Medal and Telford Premium in 1898, distinct evidence was obtained of the existence of steam in a supersaturated state, a condition long known to be physically possible, but hitherto deemed to be of negligible importance in the field of steam engineering. It was not till 1913 that super-saturation was recognised as responsible for the observational fact that the discharge from a steam nozzle was often in excess of the theoretical, a phenomenon which was very fully discussed in a paper read by Callendar before the Institution of Mechanical Engineers in 1915.
The experiments made in the McGill Laboratories with Professor Nicolson showed very definitely that within the range of experimental error, which were fixed in the main by the limitations of the indicator, the adiabatic expansion of steam was represented by the formula = constant. By direct experiment this equation has now been proved to hold good up to a temperature of 800 deg. F., and to a pressure of 300 lb. per square inch, whilst indirect methods based on the measurement of total heats indicate that its range is sensibly unlimited.
It was whilst still holding the Chair of Physics at Montreal that Professor Callendar introduced the very simple and direct method of determining the total heat of steam by throttling experiments, a method which has been extensively adopted by subsequent investigators without, in all cases, realising its limitations, whioh become of serious importance with high-pressure steam in the neighbourhood of the saturation line. The differential form of the throttling calorimeter devised by Callendar, proved capable of yielding results of extreme precision, and showed very definitely that engineers were correct in their surmise that the specific heat of steam rose as the pressure increased. Their estimates of this increase, however, varied widely and were often extravagant.
Having obtained in the manner described both the value of the adiabatic index and of the total heat of steam over a fair range of pressures, the problem arose of how the two were to be reconciled, and in this connection Callendar was responsible for a revolutionary change in the whole treatment of the properties of vapours, and which would remain of fundamental importance eyen had his experimental work been as crude as it was in fact precise. Previous investigators, in their measurements of the properties of steam, had ignored the fact that by the second law of thermodynamics certain relationships must exist between the total heat, the specific volume, and the pressure of a vapour. Thus, for example, the specific heat may he determined by direct measurement, but by the second law it is also equal to:
As a matter of fact in the steam tables published prior to Callendar’s work this relationship was far from satisfied. Amongst the best of the earlier set of tables was that of Peabody, and in these the discrepancy was in some cases as high as 20 per cent. It followed accordingly that if the work due from superheated steam were determined first from the temperature and entropy and next from the tabulated specific volumes, the two results would differ. To-day, thanks to Callendar, such uncertainties are absent from all modem steam tables, though there is still a lack of agreement as to absolute values in the case of steam at super-pressures.
The law found by Callendar for the adiabatic expansion of steam was similar in form to that of a perfect gas. The latter, however, has a specific heat which does not vary with pressure, whilst the McGill experiments showed conclusively that this was far from holding good with steam. At first it seemed difficult to reconcile the two sets of observations. Ultimately, however, Callendar recognised that the adiabatic law found, would follow automatically if the internal energy of steam could he expressed in the form E = P (V + 6) + B, where B was an absolute constant, representing the work done in separating a molecule of the liquid from its fellows.
Experiment showed that this law was very accurately satisfied by the best data available at the time, and his more recent investigations indicate that it holds good right up to the critical point. This was quite an unanticipated result, since van der Waals’ views as to the character of the border curve were universally accepted. Nevertheless, the formula was so simple and so precise within the range covered by reliable experimental data, that it was deemed safe to extrapolate it beyond this limit, a policy which has been amply justified in the outcome. The fact that the specific volume of steam was less than the theoretical was attributed by van der Waals to an inter-molecular attraction or internal pressure, which caused the volume occupied to he less than it otherwise would be. No experimental evidence had ever been brought forward proving the existence of this internal pressure, whilst Willson had definitely shown in his classic experiments of 1897 that in every mass of steam there were molecules substantially larger than would be represented by the formula Hs0. It was to these co-aggregated or compound molecules that Callendar attributed the defect of volume observed, and he showed that the laws of thermodynamics implied that to a first approximation, the specific volume of these coaggregated molecules must he a function of the temperature only. Still later it was shown that this conclusion is also a necessary consequence of the kinetic theory of gases. It was not anticipated that this simple rule would hold good at high pressures near the saturation line, hut the modification required turns out to he fairly simple.
Another important concept, due to Callendar, is that the variation in the specific heat of water is mainly, perhaps entirely, due to the fact that every liquid contains in solution, its own volume of its vapour. If its temperature be raised, more vapour is dissolved, and the apparent specific heat of the liquid is increased by the latent heat of this vapour. Independent experiments made at the Bureau of Standards, Washington, have shown that this rule represents with extraordinary accuracy the specific heat of water up to 270 deg. C. Callendar claimed that his own measurements proved the law to hold good up to the critical point. These experiments were made by his continuous flow methods, which require no correction for the heat capacity of the apparatus, and with which it is easy to guard against other errors.
In 1898, Professor Callendar left Canada and was appointed Professor of Physics at University College, London, finally becoming Professor of Physics at the Imperial College of Science in 1902.
The most striking feature of his work in recent years, at the Imperial College and carried out with the assistance of the British Electrical and Allied Industries Research Association, has been the establishment of the true character of the border curve in the neighbourhood of the critical point. This is perhaps of more immediate importance to the physicist than to the engineer, since it definitely proves the baselessness of the famous theory of van der Waals, which had held the field for some sixty years. This extremely important discovery constituted a fitting crown to nearly forty years’ work on the properties of steam, but has been so recently described at length in our columns that we need not discuss it in detail here. There is still much work to be done in establishing beyond dispute; the properties of super-pressure steam, and it was on Callendar that British engineers relied to maintain our lead in this matter. Here his loss may well prove irreparable since few there are who are gifted with Callendar’s exceptional combination of' theoretical insight and experimental ability. We; have not space to refer at length to Callendar’s many other contributions to science and technology, but may mention the important paper on the cause of. knock in petrol engines which was published in our issues of April 9,16 and 23,1926. In this, attention was drawn to the frequently forgotten fact that petrol vapour condensed when compressed, whilst steam at normal pressures superheats. It was also noted that, though the heavier paraffins have higher flash points than the petrols, they are more easily ignited."