a. [= F. thermal (Buffon), f. Gr. θέρμη heat + -AL.]
1. Of, pertaining to, or of the nature of thermæ or hot springs; of a spring, etc., (naturally) hot or warm; also, having hot springs.
1756. C. Lucas, Ess. Waters, III. 69. These thermal waters are absolutely colorless.
1800. W. Saunders, Min. Waters, Pref. 17. The thermal waters of Bath or Buxton. Ibid., iv. 352. Enriched with several thermal springs.
1859. R. F. Burton, Centr. Afr., in Jrnl. Geog. Soc., XXIX. 81. Detached boulders, blackened, probably, by the thermal fumes.
1876. M. Collins, From Midn. to Midn., III. ix. 169. The thermal city’s [Bath’s] superb crescents.
1898. Allbutt’s Syst. Med., V. 1000. Simple thermal baths at 90° F. or under commonly tend to reduce the pulse-rate.
2. Of or pertaining to heat; determined, measured, or operated by heat.
The thermal capacity of a body (cf. CAPACITY 1 c, HEAT sb. 2 d) is measured by the quantity of heat required to raise its temperature one degree; the thermal efficiency of an engine, by the ratio of the work done by it to the heat supplied to it. Thermal storage: a system of storing water at high pressure and temperature in vessels above the boilers during hours of low load in electric generating stations. Thermal unit: a unit of heat; the British thermal unit (abbrev. B. Th. U.) is the amount of heat required to raise the temperature of a pound of water at its maximum density through one degree Fahrenheit.
1837. Brewster, Magnet., 267. The thermal and the magnetic equators are connected … with the thermal and magnetic poles.
1870. Tyndall, Lect. Electr., § 10. To produce both magnetic and thermal phenomena.
1876. Catal. Sci. App. S. Kens. Mus., § 1056. The heat is calculated as follows, either in calories or British thermal units.
1884. Knight, Dict. Mech., Suppl., 891/1. Thermal Alarm for Hot Boxes.
1910. J. G. Horner, in Encycl. Brit., IV. 148/2. In some cases where the work required is very intermittent, thermal storage is employed.
1910. H. L. Callendar, ibid., V. 61/1. The specific heat of a substance is sometimes defined as the thermal capacity of unit mass. Ibid., XIII. 137/1. English Engineers usually state results in terms of the British Thermal Unit (B. Th. U.). Ibid., 138/1. The improvement in thermal efficiency obtained by expansive working.
3. fig. Heated with passion; erotic, passionate, impassioned.
1866. Lond. 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.
Hence Thermality, thermal condition; Thermally adv., in a thermal manner; by means of or with regard to heat.
1884. trans. 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. Tyndall, Fragm. Sc. (1879), I. xvii. 449. The experiments proved rock-salt to be coloured thermally.
