1933 Jrnl. Royal Aeronaut. Soc. 37 678 Herr Hirth had gained a great deal of experience regarding ‘thermals’, that is to say, ascending currents of warm air which can be used for soaring as distinct from soaring in the currents beneath clouds.

1950 ‘N. Shute’ Town like Alice 229 She rolled over on her back and watched a seagull soaring in the thermals from the island.

1962 Amer. Scientist L. 180 Thermal soaring is the method most commonly used by soaring birds.

1974 ‘G. Black’ Golden Cockatrice iii. 60 He had been using that moving water belt beyond the harbour as a bird uses a thermal.

1936 Archit. Rev. 79 255/3 For greater heights the second and more interesting method is employed; what is known as ‘thermalling.’ This is the utilization of the columns of rising air that are always in existence under certain weather conditions.

1974 Reader's Digest Feb. 89 With a Rogallo you can also do another type of soaring, called thermaling, where you circle in chimney-like updrafts of warm air that rise from sun-heated ground.

1756 C. Lucas Ess. Waters iii. 69 These thermal waters are absolutely colorless.

1800 W. Saunders Treat. Mineral Waters Pref. 17 The thermal waters of Bath or Buxton.

1800 W. Saunders Treat. Mineral Waters iv. 352 Enriched with several thermal springs.

1859 R. F. Burton Lake Regions Central Afr. in Jrnl. Royal Geogr. Soc. 29 81 Detached boulders, blackened, probably, by the thermal fumes.

1876 M. Collins From Midnight to Midnight III. ix. 169 The thermal city's [Bath's] superb crescents.

1898 T. C. Allbutt et al. Syst. Med. V. 1000 Simple thermal baths at 90° F. or under commonly tend to reduce the pulse-rate.

1866 London Rev. 18 Aug. 178 Instead of the establishment in England of a thermal school of poetry; instead of the revivification of a grand (and wicked) old Paganism.

1927 Physical Rev. 29 367 Ordinary electric conductors are sources of random voltage fluctuations, as a result of thermal agitation of the electric charges of the conductor.

1966 C. R. Tottle Sci. Engin. Materials v. 117 The mean free path l depends on the thermal agitation of the lattice.

1925 Jrnl. Iron & Steel Inst. 112 489 Thermal analysis was followed by determination of the hardness and a study of the micro~structure of the test-pieces.

1960 B. Chalmers & A. G. Quarrell Physical Exam. Metals (ed. 2) iii. 183 The simplest method of carrying out a thermal analysis is to place the specimen in a furnace which is arranged to have a negligible temperature gradient over a zone somewhat greater than the length of the specimen.

1971 Gloss. Soil Sci. Terms (Soil Sci. Soc. Amer.) 21/1 Thermal analysis (differential thermal analysis), a method of analyzing a soil sample for constituents, based on a differential rate of heating of the unknown and standard samples when a uniform source of heat is applied.

1951 Jrnl. Royal Aeronaut. Soc. 55 757/2 A new barrier is faced after ‘climbing’ the sonic barrier, namely the Thermal Barrier.

1958 C. C. Adams et al. Space Flight 265 The MA-2 is a special suit that is ventilated for travel through the thermal barrier, and the MA-1 is a new ARDC helmet.

1972 Sci. Amer. July 33/3 This combination of conditions is all that is needed to produce the X rays, since accelerated charges are a source of electromagnetic radiation. A compact name for the process is ‘thermal bremsstrahlung’.

1880 W. Thomson in Encycl. Brit. XI. 558/2 Regnault's measurements of the thermal capacity of water at different temperatures.

1910 H. L. Callendar in Encycl. Brit. V. 61/1 The specific heat of a substance is sometimes defined as the thermal capacity of unit mass.

1950 Sci. News 15 Pl. 16 (caption) Slip~lines in pure zinc after exposure to 50 thermal cycles between 30°C and 150°C (× 500).

1963 B. Fozard Instrumentation Nucl. Reactors xiii. 170 Thus the reactor can be operated under virtually isothermal conditions over a wide range of load, with consequent constancy of steam conditions and absence of thermal cycling.

1898 Public Health Papers & Rep. 1897 (Amer. Public Health Assoc.) 23 86 In determining the thermal death point cultures should always be moist.

1968 R. R. Ernst in Lawrence & Block Disinfection, Sterilization & Preservation vii. xliii. 707/2 The thermal death point is the lowest temperature at which a suspension of bacteria is killed in 10 minutes. This standard has been almost abandoned.

1916 S. Chapman in Proc. Royal Soc. A. 93 10 We may call D₁₂, D₁₂′, D_p, and D_T respectively the coefficients of diffusion, forced diffusion, pressure diffusion, and thermal diffusion. The definition of D₁₂ agrees with that usually given for the coefficient of diffusion. The other coefficients seem to be defined here for the first time.

1962 Newnes Conc. Encycl. Nucl. Energy 357/2 The separations achieved in a convection~free system are small, and are only used to determine the magnitude of the thermal diffusion effect and to provide information on intermolecular force fields.

1880 W. Thomson in Encycl. Brit. XI. 581/2 It is k/c, not merely k, that expresses the quantity of the substance on which the phenomenon chiefly depends. We therefore propose to give to k/c the name of thermal diffusivity.

1973 J. G. Tweeddale Materials Technol. I. iv. 95 Thermal diffusivity (a) is important when it is necessary to consider the effects of temperature differences set up in a material during transfer of heat.

1973 J. G. Tweeddale Materials Technol. I. iv. 95 Both thermal conductivity and diffusivity cease to have much meaning for the liquid state since in that state the principal mechanism of transfer becomes convective mixing.

1910 Encycl. Brit. XIII. 138/1 The improvement in thermal efficiency obtained by expansive working.

1982 Daily Tel. 20 Aug. 5/2 Their passive infra-red viewers, image intensifiers, and thermal imagers were excellent.

1970 Nature 19 Sept. 1182/1 The technique of thermal imaging—picking up infrared radiation from the human body and displaying the resulting thermal image on an oscilloscope—..has been used to map the flow of warm arterial blood into, for example, tumours and varicose veins.

1980 Times 4 Aug. 17/2 Thermal imaging..involves the visualization of objects and scenes by detecting and processing the infra-red energy they emit.

1973 ‘K. Royce’ Spider Underground viii. 119 Someone must be on tap to answer awkward questions if Old Bill [sc. the police] arrives. The thermal lance men will be below.

1977 F. Webb Go for Out vii. 125 A modern peterman needs explosives—else thermal lances.

1930 F. B. Llewellyn in Proc. IRE 18 244 The importance of this noise, which will be termed ‘thermal noise’, in high-frequency radio receiving circuit design will be discussed.

1975 D. G. Fink Electronics Engineers' Handbk. xxii. 60 Thermal noise for the most part originates in the first stages of the radio receiver and sets the minimum signal amplitude acceptable for a given signal-to-noise ratio.

1978 T. Gifford Glendower Legacy 39 He..glanced out the wide thermal-pane window.

1965 R. G. Kazmann Mod. Hydrol. iv. 109 The so~called thermal pollution of streams has resulted primarily from the installation of steam-electric generating plants along our rivers.

1969 Financial Times 9 Jan. 4/6 The danger of ‘thermal pollution’ is greatest where electric and other power plants return to rivers and streams water that has been heated by between six and 16 degrees Centigrade. This often proves deadly to fish.

1977 I. M. Campbell Energy & Atmosphere v. 86 There is unlikely to be a thermal pollution problem of any importance on a global basis within the foreseeable future.

1982 Sci. Amer. Dec. 93/1 Thermal printers, which cost less than $500, burn an image into a special paper at a rate of some 50 characters per second.

1962 J. H. Simpson & R. S. Richards Physical Princ. Junction Transistors ix. 210 In extreme cases this positive feedback may lead to a catastrophic increase in temperature—a phenomenon commonly called ‘thermal runaway’.

1975 G. J. King Audio Handbk. iv. 106 Since f.e.t.s are less temperature sensitive than bipolar transistors, temperature compensation is not necessary, neither can thermal runaway occur, for I_o tends to fall with increasing temperature.

1925 Dental Rec. 45 627 It has been argued that grinding the enamel in preparation for the crown renders a tooth susceptible to thermal shock, with subsequent destruction of pulpal structures.

1962 Research XV. 80/1 Uranium polycarbide..is much more resistant to thermal shock and thermal cycling.

1974 Sci. Amer. Dec. 95/2 They are not die-cast in significant quantity now because the thermal shock to the metal components, including the mold, is so severe that the life of the components is short.

1910 J. G. Horner in Encycl. Brit. IV. 148/2 In some cases where the work required is very intermittent, thermal storage is employed.

1933 Archit. Rev. Oct. p. xl/1 During the last two or three years an entirely new kind of cooking appliance has made its appearance in England. It is known as the thermal storage or stored heat cooker.

1961 Guardian 12 June 6/6 A domestic thermal storage heater is now available.

1972 Oxf. Univ. Gaz. CII. Suppl. No. 8. 3 Work has begun on the installation of a second thermal storage boiler.

1853 Trans. Royal Soc. Edinb. 20 170 The mechanical equivalent of the ordinary thermal unit.

1876 Catal. Special Loan Coll. Sci. Apparatus S. Kensington Mus. §1056 The heat is calculated as follows, either in calories or British thermal units.

1910 Encycl. Brit. XIII. 137/1 English Engineers usually state results in terms of the British Thermal Unit (B. Th. U.).

1943 Gloss. Terms Electr. Engin. (B.S.I.) 14 A B.t.u. is equivalent to 1054 joules.

1955 Sci. Amer. July 58/1 Coal supplied only 34 per cent of the nation's total B.T.U.'s (British thermal units).

1964 H. S. Hvistendahl Engin. Units vii. 110 The legal definition of the Btu is the amount of heat required to raise 1lb of water from 60 to 61°F at standard atmospheric pressure.

1950 Canad. Jrnl. Res. A. 28 434 The thermal column of the Chalk River pile was used as a large block of scattering material with a high flux of thermal neutrons.

1963 B. Fozard Instrumentation Nucl. Reactors xiii. 166 A count rate from the fission chamber of 10⁵ c/s..is produced by a neutron flux, in the thermal column, of about 5 × 10⁶ neutrons cm^—2 sec^—1.

1938 Physical Rev. 54 235/1 (heading) Collimated, variable energy beam of pure thermal neutrons.

1945 H. D. Smyth Gen. Acct. Devel. Atomic Energy Mil. Purposes viii. 79 We now introduce a factor f, called the thermal utilization factor, which is defined as the probability that a given thermal neutron will be absorbed in the uranium.

1966 C. R. Tottle Sci. Engin. Materials x. 236 Fast neutrons may be moving at speeds of the order of 10¹⁰ cm sec^—1 with an energy of 1 to 10 MeV. When slowed down to a similar order of energy to that of the thermal vibration of atoms (hence called thermal neutrons) the speed is about 10⁵ cm sec^—1 at an energy of 1 eV.

1949 H. Etherington in S. C. Rothmann Constructive Uses of Atomic Energy v. 76 In a thermal reactor fission is produced by neutrons that have been slowed approximately to thermal velocities.

1971 Nature 23 July 211/1 The companies say that they have between them a good deal of experience in building thermal reactors of several types.

1959 Listener 19 Nov. 872/1 At slow or ‘thermal’ speeds neutron capture by nuclei of Uranium 238 is less important.

1936 Physical Rev. 49 520/1 It is therefore not necessary to ascribe all large cross sections to neutrons of thermal velocities.

1884 tr. L. Brachet's Aix-les-bains i. 74 We must pay special attention to the thermality, which is the sole bond of union [etc.].

1871 J. Tyndall Fragm. Sci. (1879) I. xvii. 449 The experiments proved rock-salt to be coloured thermally.