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Techniques have been developed for measuring the strain and thermal histories of fluid elements as they move from the die lips to the freeze line. Motion pictures were analyzed to determine the rates of extension in the machine and transverse directions. A radiation pyrometer was used to measure the temperature of the film. These techniques were used to study the film blowing of polyethylene; a 2.5-in. diameter die was used, and blow-up ratios in the range of 1.8 to 3.4 were employed. Film thickness ranged from 2 to 4 mils. The maximum measured extensional strain rates in both the transverse and machine direction were in the range of 0.15 to 0.6 sec−1. Standard shrinkage and impact tests were performed on the finished films, and an attempt was made to correlate the results with several simple empirical norms of the strain history. No correlation could be discerned. The results of this study are inconsistent with some popular ideas about the origin of orientation in blow films, but they are consistent with some recently published data on the influence of deformation on orientation in melt-drawn capillary extrudate.

We have measured the electrical resistivities of a series of thin polycrystal and single-crystal tungsten wires annealed and quenched in both ultra-high vacuum and superfluid helium. For a given sample the quenched-in resistivities were very nearly the same for both ultra-high vacuum and superfluid quenches. We infer from this result that the quenched-in resistivities are not due either to quenohed-in helium atoms or to atmospheric contamination as recently suggested by Evans. On the other hand, the magnitude of the quenched-in resistivity varied somewhat from sample to sample. Measurements with an optical pyrometer suggest that this variation is not due primarily to differences in temperature of the samples just prior to quenching. Analysing both our data and other data recently published we conclude that impurities must play an important, but not yet adequately understood, role in determining the magnitude of the resistivity retained in quenched tungsten.

The flow of polymer melts in cylindrical, annular, and slit dies has been examined. Large temperature rises at the outer surface of the extrudate were measured with an infrared pyrometer. Calculations show that severe radial temperature gradients exist in these flow geometries under conditions similar to those encontered in polymer processing and in viscometry measurements. A common method of estimating the average temperature rise from the total mechanical energy input seriously underestimates the maximum temperature rise. A numerical solution of the flow and energy equations models the flow in all three geometries. A very simple Nusselt number correlation allowed an estimate of the temperature rises possible if heat transfer with the die wall occurrs. Good agreement was obtained between predicted and infrared measured melt surface temperature rises. The pressure drop gives only an indication that nonisothermal flow is occuring and is not sensitive enough to distinguish the type of heat transfer boundary condition present. The mathematical model presented could be helpful in die design and in process modeling, allowing the designer to obtain some knowledge of the kind of flow situations which might be encountered.

Samples held at pressures up to 260 kilobar in a diamond anvil pressure cell have been heated to very high temperatures by means of a laser beam introduced through one of the transparent diamond anvils. A 7 J pulsed ruby laser is able to produce temperatures as high as 3000°C in a high pressure sample. A 60 W cw YAG laser is able to produce sustained temperatures up to 2000°C. An optical pyrometer has been used in the latter case to measure the brightness temperature with an accuracy of ±50°C. The ruby laser has been successful in directly converting graphite to diamond; the YAG laser has made it possible to show that (Fe,Mg)2SiO4 disproportionates to (Fe,Mg)O plus SiO2 (stishovite) at pressures in excess of 200 kilobars and temperatures above 1000°C.

The hybrid combustion of polystyrene and oxygen styrene copolymer has been studied. The linear regression rate r and total mass flow of fuel mf have been measured at different oxygen flow rates and at different times intervals. It is found that the regression rate decreases with time. Detailed analysis of the data shows that it is due to radiative heat transfer from the flame zone to exhaust gases.

The normal spectral emittance of Ti and Zr was obtained in the temperature range 1100 to 1800 K and wavelength 0.645 μ for electrochemically polished, mechanically polished and 60 grit ground surfaces at a pressure below 10-8 mm Hg. The emittance at the melting point of both metals was obtained by extrapolation of an empirical equation fitted to the experimental data obtained for the electrochemically polished surface and was found to be in good agreement with reported values. The considerable grain growth on the surface affected the emittance. The emittance was found to increase with temperature up to 1300 K and then decreased with further increase in temperature.

The measurement of radiation (ultra-violet, visible, or infrared) from a surface as a means of knowing the surface temperature has been found useful in many applications. One of the simpler types of instruments which uses this principle is a brightness pyrometer. The brightness pyrometer relates radiation to temperature on the basis of radiation magnitude, which is a function of temperature, but the output of the brightness pyrometer is also a function of a material property known as emissivity. While many brightness pyrometers have compensation control for different values of emissivity, knowing the emissivity constant is left for the user to find through such aids as handbooks of materials and physics texts. Even then, the emissivity may vary as a function of the particular chemical content and environment to which the material is subjected. Hence, Raytheon felt there was a need for a device to measure emissivity simultaneously with other radiation measurements and within a fraction of the time span used by the heating process.

Modern day pyrometry permits the measurement of temperature with maximum uncertainties ranging between about O.1°C at 1064°C (gold point) and 2°C at 3525°C. These uncertainties refer to the realization of the International Practical Temperature Scale (IPTS) and represent the level of accuracy a temperature per se can be determined under optimized conditions. Unfortunately, the measurement of a material property as a function of temperature imposes experimental constraints which seriously degrade the inherent accuracy of the temperature measurement system, often to unknown levels. Consequently, in situ temperature calibrations are required which must employ the use of a well characterized reference material compatible with the environment of the experiment. Suitable secondary temperature reference standards are not generally available and this lack is being addressed by the High Temperature Commission (IUPAC) through its current melting point program on Y2O3 and formerly by its efforts on Al2O3.Th...

The technique of derivative thermal analysis, dTA, which plots sample temperature vs rate of change of sample temperature, has been refined in this apparatus to produce calibrated derivative thermal analysis curves in units of degrees and degrees/second. The scaling factors of 1 K=2 mV and 1 K/sec = −100 mV permit calibration to 5273 K, materials permitting, with digital temperature readout. The derivative function provides high sensitivity for detecting very weak fast phase transitions by observing thermal arrests in linear heating and cooling curves. A companion automatic temperature controller holds the furnace temperature constant, or programs it up or down at a linear rate of 0.1 K/sec to 10 K/sec. Light from the incandescent sample and surrounding furnace is divided into two paths by a beam splitter. One path to an optical pyrometer provides temperature calibration. Light in the second path is sensed by photo transistors that measure the sample and furnace temperatures. The temperature signal is lin...

A new method is proposed to deal with the spectral width of optical pyrometers. A constant reference wavelength and a radiance correction factor are introduced instead of a temperature dependent effective wavelength as is used in the conventional method.

A surface heated by a frictional impact was simulated by the discharge of a bank of capacitors through a strip of tungsten foil. The resultant rise and fall of temperature were investigated by means of a two-color pyrometer. The heated foil was exposed to various concentrations of flammable gases, and the probability of ignition was investigated as a function of several variables, including gas concentration, temperature profile, and foil size. It was found that the peak temperature necessary for ignition decreased as the width of the foil was increased, and that 7% was the most easily ignitable concentration of methane in air. The size of the heated surface was of the order of 200 mm 2 and this necessitated a working range of peak temperatures of approximately 1500°C to 2200°C in the study of the ignition of methane-air. Some preliminary experiments indicated that propane-air could be ignited at much lower temperatures.

The electrode temperatures of graphite during the arc and post‐arc periods associated with the recovery characteristics in argon were measured. The photoelectric pyrometer used was sensitive to ir rays (corresponding to 1000–4000°K), but insensitive to the rays radiated from the arc plasma. The anode drop relating to the anode temperature was derived as 2.9 V for the quiet arc where the evaporation and radiation losses were considered to be small, and the electron current density derived from the arc‐root diameter at the cathode was found to be much larger than that derived from the Dushman‐Richardson equation, and had to be considered even in case of refractory electrode F‐T (field and thermionic) electron emission mechanism. On the other hand, the polarity effect on the reignition tests suggests that when the cathode temperature increases above about 1600°K, Paschen's law will fail.

Construction and operating details are given for an apparatus used for testing small refractory specimens under tensile or compressive loads up to 2200°C. An electrical resistance, graphite tube furnace can be made to heat at a uniform rate of 0° to 1000°C. per hour and to shut off at a predetermined specimen temperature or deformation. Temperature is measured by a radiation pyrometer and controlled by a duration-adjusting, impulse-type controller. Deformation is measured by means of a micrometer dial gauge and transmitted through a slide wire rheostat to a bridge-type recorder. A standard deviation of 22°C. for compression failure and 24°C. for tensile failure was determined on a periclase refractory.

In my former communication on a new Register-Pyrometer, which has been honoured with a place in the Philosophical Transactions for 1830, I stated that I hoped, at some future period, to be able to lay before the Society the results of some experiments upon the dilatation of metals to their melting points ; and I now purpose to redeem this pledge. My previous observations upon the subject of expansion, were directed chiefly to the object of establishing what degree of confidence might be re­posed in the instrument as a measure of temperature ; and I was able, I trust, to exhibit such an accordance between the measures which it had afforded and those of the best experimenters, long previously obtained with various metals to the boiling point of water, as fully to establish its sufficient accuracy. The comparison however which I most relied upon, was with the experiments of MM. Dulong and Petit, upon the expansion of platinum and iron to the high temperature of 572° Fahr. ; and as this is a point of fundamental importance, I shall still further strengthen it by a comparison with the results obtained by the same distinguished philosophers with copper, the only other solid metal to which they extended their inquiries.

The emissivity errors of total, partial and monochromatic radiation pyrometers for use in the temperature range 500-800° K are discussed theoretically. The pyrometer output is expressed as a power law of absolute temperature with an exponent n which varies with temperature and the spectral response of the pyrometer. The emissivity error decreases as n increases. It is shown that n increases as the spectral response of the pyrometer is restricted to shorter wavelengths in the near infra-red region.

A pyrometer, which covers the temperature range 200 to 900 deg. C. (390 to 1,650 deg. F.) with a response time of 10−3 seconds, has been developed for studying the temperature of stationary and moving surfaces. The values of the emissivities of bright and oxidized steel surfaces, determined by this method, agreed with other published work. The pyrometer has been used to determine the temperature of the surface of a railway tyre, during brake applications under various conditions, just as it emerged from beneath the brake block. Evidence is adduced to prove that the temperatures measured are not very different from those actually under the block. It is shown that the possible change in emissivity of the tyre steel is insufficient to invalidate the results. The variation and extent of the area of contact between brake block and tyre were investigated simultaneously with the temperature measurement. It was shown that high tyre surface temperatures (over 800 deg. C.; 1,470 deg. F.) are an inevitable result of “strip braking”. The preferred formation of heat spots between the spokes of the wheel, and the unequal growth of heat spots across and along the tread due to tyre distortion, were examined. An attempt to eliminate strip braking by reducing the length of the standard brake block to three-quarters, one-half, and one-quarter of its original length was made. It was found that reducing the brake block to one-quarter of its original length completely inhibited heat spot formation, reduced by a factor of 2 the standard deviation of the stopping times under standard conditions, and reduced the maximum temperature attained during brake application from over 800 deg. C. (1,470 deg. F.) to under 400 deg. C. (750 deg. F.). The deleterious formation of martensite was thus eliminated. It was found that the wear of the half-length brake blocks, expressed on a thickness basis, was not twice but maybe equal to that of a full-length block. Since the cost of a brake block is somewhat proportional to its size it follows that a shorter block may be more economical than a full-length block. It is concluded that the optimum size of a railway brake block must be determined separately for each material and set of operating conditions.

1. The data of thermal investigations with a recording pyrometer, and also investigations of the processes of decomposition of barium peroxide compounds, made it possible to establish the individuality of each of these compounds: BaO2, BaO2·8H2O, BaO2·H2O2, and BaO2·2H2O2. 2. On dehydration BaO2·8H2O is gradually converted to BaO2, intermediate hydrates being formed. 3. The decomposition of BaO2·2H2O2 may take place either through the intermediate stage BaO2·H2O2 or through BaO2·2H2O, which does not exist independently, depending on the external conditions. 4. BaO2·2H2O2 is a relatively stable compound if residual water and excess hydrogen peroxide are carefully removed from it by drying over H2SO2 at 0°. 5. Anhydrous barium peroxide in the dry state is a quite stable compound; it begins to decompose vigorously above 500°.

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A method for accurately observing phase changes at high temperatures has been developed; it employs a microfurnace and uses samples of oxide mixtures weighing less than 1 mg. The samples were observed and their temperatures measured with an optical pyrometer specially adapted for this purpose and calibrated for the furnace radiation. An electrically heated resistance strip, in general of molybdenum, allows melting and crystallization of the oxide mixtures at any desired speed. The samples were placed directly on the strip and could be quenched by interruption of the current flow.The binary system, BaO–TiO2, was investigated. The existence of four compounds, BaTi4O9, BaTi2O5, BaTiO3, and Ba2TiO4, was demonstrated by liquidus curves and x‐ray diffraction. A phase change of BaTiO3 below the solidus temperature was observed; all oxide mixtures with less than 80 mole percent TiO2 showed this intermediate BaTiO3 phase at about 1450°C.Single crystals of BaTi4O9, BaTi2O5, and BaTiO3 were grown from ternary melts ...

The temperature vs time curve of a cooling or heating incandescent material is displayed either on a cathode ray oscilloscope or a strip chart recorder. Temperatures at which phase transitions occur are seen as discontinuities in the curves. The temperature‐sensing device is a photomultiplier tube. The sample is heated in an eddy current concentrator by induced radio‐frequency currents. Light from the sample is divided by a beam splitter between the phototube and an optical pyrometer which is used for temperature calibration. The temperature range displayed for a fixed starting temperature may be reduced by opposing the phototube's output voltage with an adjustable fixed voltage. Typical cooling curves are included.

In view of the enormous discrepancies at present existing in estimates of high temperatures, it is exceedingly desirable that strictly comparable thermometric standards should be issued by some recognised authority. Professor J. J. Thomson, in the course of a conversation which I had with him towards the close of 1885, suggested th at such standards could be issued in the form of platinum wire, the change of electrical resistance with temperature being determined by comparison for each specimen before issuing. The object of the present investigation was to test whether, in spite of the B. A. report on the Siemens pyrometer (1874), pure platinum wire might not be possessed of the necessary qualifications for such a standard.

An attachment to a horizontal goniometer for X-ray powder diffraction at temperatures up to about 2,000°C in a vacuum in the 10−9 torr range is described. Specimen heating is by direct contact to a resistance strip heater with provision for electron beam heating. Temperature measurement is by thermocouple or optical pyrometer. High-temperature parameter measurements on vanadium are presented as one of the examples of the capability of the apparatus.

The fabrication and photo-response data are described for n-n CdSe–Ge heterojunctions which were made by vacuum evaporation of CdSe. A model is given which theoretically explains part of the shape of the spectral dependence of the photovoltage produced at zero bias. In forward bias, with the CdSe positive, the sign of the photovoltage changes and this points to a double-depleted band diagram dominated by acceptor-type interface states. Two applications of the photocharacteristics are briefly outlined: one describes a possible null-detecting frequency meter and the other a null-detecting optical pyrometer. Die Praparation und das Photoverhalten von n-n-CdSe–Ge-Heteroubergangen, die durch Vakuum-Aufdampfen von CdSe hergestellt wurden, werden beschrieben. Ein Modell wird angegeben, das theoretisch die Form der Spektralabhangigkeit der Photospannung ohne Vorspannung teilweise erklart. Bei Vorspannung in Durchlasrichtung, wobei CdSe positiv ist, andert sich das Vorzeichen der Photospannung, was auf ein doppelt-verarmtes Bandschema hinweist, das durch Grenzflachen-Akzeptorzustande bestimmt wird. Zwei Anwendungsmoglichkeiten der Photocharakteristiken werden kurz angefuhrt: ein moglicher null-anzeigender Frequenzmesser und ein null-anzeigendes optisches Pyrometer.

An examination of the sources of errors leads to the conclusion that in many instances the methods of color pyrometry can improve the precision of industrial temperature measurements. This is the case in the measuring of the temperature of oxidized and other surfaces with a rough structure, of clean surfaces of many metals in different conditions, of components in closed furnaces (through windows, etc.). and in many other cases. Objective color pyrometers are particularly useful, for they have a high instrument accuracy and measure directly the redblue ratio. However, in making the color measurements it should be remembered that the selective, especially the changing, emission or absorption produces an error which often exceeds the error of the brightness method.

The method described uses a photomultiplier in conjunction with an infra-red image converter to measure changes in surface temperature of the cathode of an oscillating magnetron during microsecond pulses. These instantaneous changes in temperature are displayed as pulses on the screen of a cathoderay oscillograph. The procedure is given of calibrating the apparatus against an optical pyrometer. Changes as small as 2° C in 800-900° C have been detected (solid angle equals 2.5 x 10-3 steradians).

The construction of a general purpose radiation pyrometer using a lead sulphide photocell is described. Based on a comparison principle, the instrument is independent of ambient temperature variations. The temperature range covered is 200-1000° C with an accuracy of ±5° C and a response time of less than 0.1 s.

The principles of two- and three-colour radiation pyrometers are described and the literature upon these instruments is reviewed. The advantages and limitations of these methods of temperature measurement are discussed with particular reference to the measurement of temperatures below 1500°C.

The standard temperature scale is defined and methods of realizing it both in laboratory and in factory practice are outlined. Methods of measuring temperature from very low values to the highest obtainable are described. The use of thermocouples, the errors encountered in the use of both base metal and rare metal thermocouples, and the methods used to avoid these errors are discussed. Thermocouples are useful in measuring temperatures up to about 1000 to 1500°C. Beyond the range of thermocouples and sometimes even in this range it is necessary to use some means of measuring temperature that depends on the energy radiated from the source under consideration. For this class of work the optical pyrometer is recommended as one very good method. Different forms of optical pyrometers are discussed and the advantages and disadvantages of these types are pointed out. The conclusion is reached that for many types of work the disappearing-filament type of optical pyrometer has certain advantages over other forms. Some of these advantages are pointed out and reasons given for the selection of this pyrometer. The necessity for the use of a monochromatic screen with a pyrometer is discussed and a list of the various screens available are given. Reasons are given for the general choice of a red screen for this work. In the use of an optical pyrometer it is at times necessary to know something concerning the wave-length of the light used. This brings up the question of the effective wave-length of the screen used. The effective wave-length is defined and methods given for determining and using this effective wave-length in optical pyrometry. It is shown that with a well-calibrated screen just as definite results can be obtained as with a spectrometer for determining wavelength, and the advantages of the screen over the spectrometer are set forth. Methods of calibrating optical pyrometers are discussed which bring in the idea of a black body. Methods of realizing the theoretical black body are given together with some experimental results along this line. The use of absorbing screens in extending the scale of an optical pyrometer is outlined and methods are given of obtaining the transmission of the absorbing screens so that it is easy to calculate the extension of the temperature scale with a particular screen. The kind of an absorbing screen needed for this work is shown and the advantages and disadvantages of the absorbing screens are given. Accuracy tests are included in which it is shown that very good agreement can be obtained in the use of a disappearing-filament optical pyrometer by untrained or slightly trained observers. Results are also given to show what accuracy may be expected from experienced observers from this form of pyrometer.

Phase diagrams are drawn for many metals under some approximations, and “vacuum evaporation temperature” is estimated as the temperature corresponding to 10−1 mm. Hg of vapor pressure. This temperature agrees well with that given by Yarwood. The rate of evaporation is calculated, and the result agrees well with experience, at least, for silica gel. As for shadow casting, it is concluded that high temperature of specimen and low pressure of air in the vessel are the necessary conditions to obtain clear shadow. The temperature of evaporating silica gel is measured with optical pyrometer, and a satisfactory result is obtained.

Description of a recording pyrometer set up, the conditions to be observed and the benefits derived.

Expressions are derived for the errors of the two types and from them a chart, from which these errors can be calculated for any pyrometer for all possible values of emissivity. The limitations of both types for direct measurement of true temperature are discussed and the errors likely to result when true temperatures are calculated from apparent temperature from previous knowledge of emissivities. An expression is derived for the relation between the emissivities (1 and 2) at the two-colour pyrometer wavelengths (λ1 and λ2) corresponding to a given ratio Z between the error of the two-colour pyrometer and the error of a brightness pyrometer working at one of the wavelengths (λ2). This information is plotted as a chart of 1 against 2, the application of which to a practical problem is demonstrated. A more complex type of ratio pyrometer is put forward, enabling broader assumptions to be made regarding the emissivity/wavelength relation.

Calculations are given for determining the errors, caused by water vapour absorption, in temperature measurements with radiation pyrometers of different optical systems. Some experimental checks are included.

Imaging techniques and apparatus have been developed for measurement of thermal conductivity of small size samples at temperatures from 1000°C to the melting point of the material. Details of the method for heating the sample in an electric arc imaging furnace, measuring the temperature distribution over the sample surface with an optical pyrometer, and measuring the heat flux leaving the back of the sample with a thermopile are given. A computational procedure is described suitable for machine computer use.

Behavior of phenolic nylon under stepwise-varied heating conditions was investigated experimentally. Arbitrary transient heating pulses were generated by major variations in radiative heating and minor variations in enthalpy and pressure. Three rates of change of applied heating r = (Aq/Ar) from 11 to 44 w/cm-sec were provided by varying pulse times. Mass of material pyrolyzed rnp char interface recession Xc and surface recession Xs were determined over partial and complete pulses. The average degradation rates (rnp/T or XC/T) increased with increasing r, but the average surface recession rates (Xc/r) were approximately the same for all pulses. The measured transient heating results were compared with material performance calculations based on steady-state heating test results. For minimum and maximum r, respectively, measured degradation (ntp or Xc) was about 15% less and 30% more than calculated. The measured and calculated surface recession agreed within ±10% over all pulses. Although the quantitative results apply only to the phenolic nylon material and the transient test conditions of the present investigation, the effects are expected to be applicable to charring ablators under flight conditions. It is concluded that transients in material response in an increasing heating environment result in accelerated material degradation.

A review of those fundamental facts and relations concerning polarized light with which the reader should be familiar is given. The devices which serve as the polarization elements of all instruments are then described, followed by a description of half-shade azimuth polarimeters, elliptic polarimeters, Tool's general polarimeter, and a Universal polarimeter designed at the Bureau of Standards. The practical applications of polarimeters to saccharimetry, photometry, colorimetry, pyrometry, determination of the optical constants of absorbing media, mechanical stress analysis and testing of the optical homogeneity of glass are all briefly described.

A method is reported in which visual observation of the incandescent filament by means of commercially available television equipment is combined with temperature measurements along the coil. The features of an installation, consisting of a 'Plumbicon' camera tube, monitor and video-tape recorder in conjunction with a quotient pyrometer measuring the radiation intensity at two wavelengths, are described. Some examples of experimental results obtained with various types of tungsten halogen lamps are illustrated by photographs taken from the television monitor screen and by temperature recordings. Though still pictures can give only a faint idea of the information value of video-tape recordings the reported method is a valuable tool for investigating the dynamic processes occurring in the filament under various burning conditions.

A radiometric method for measuring surface temperatures greater than 50° c which may change as rapidly as 200° c per second has been applied to textile fabrics during exposure to intense thermal radiation. Calibration of the pyrometer for different fabrics was derived from the known boiling temperatures of a number of pure substances. Prominent features found in the temperature time curves of fabrics relate to the evaporation of contained moisture and to the melting of the fibre.

The use of a portable surface-brightness photometer of the polarisation type for the measurement of the fraction of the incident light transmitted by an optical instrument or reflected by a mirror or system of mirrors, and for the measurement of the relative brightness of different parts of the field of view of an optical instrument, is described. The instrument employed is a Wanner optical pyrometer (Cambridge and Paul Inst. Co.) with some modifications to render it suitable for such work. An addition to the instrument is described which removes the danger of error due to polarisation of the incident light.

The problem of raising the accuracy in the construction and transmission of the International Practical Scale of Temperature in the high-temperature region can be solved by altering the calibration procedure by replacing pyrometers by comparators and, at the same time, improving the metrological parameters of the standard measures of temperature by standard temperature-calibrated lamps. In a broad temperature range the accuracy of the construction and transmission of the International Practical Scale of Temperature may be raised by a transition to thermofrequency methods of measuring the temperature, including the use of quartz linear frequency thermometers. The development of thermofrequency methods may be the foundation for the organization of remote “telemetric” comparisons of temperature standards and temperature measuring instruments; ultimately, this will ensure the desired high accuracy and unity of temperature measurements in all the fields of science, technology, and industry.

Results of the experimental determination of the enthalpy and heat capacity of molybdenum between 700°C and 2337°C are presented in the form of a table, diagram and equations. Experimental data were obtained by the method of mixtures using a massive calorimeter with an isothermal shell. A sample was heated to a high temperature in a furnace with a tungsten heater, in a vacuum or in an argon medium. The paper deals with some methods of an experimental determination of the enthalpy at very high temperatures. The experimental results are compared with those in the literature. For the determination of enthalpy the limiting accidental error was ±0.4 per cent using a thermocouple to measure temperature up to 1300°C, and ±0.9 and ± 1.2 per cent using a disappearing-filament optical pyrometer for temperatures up to 2000°C and 2400°C, respectively.

By means of two photo-electric cells with suitable coloured filters the energy radiated in two distinct spectral bands is compared. By combining the ascertained sensitivities of the two cells and their filters with the radiation law the black-body temperature of the radiator can be determined.