202 Proceedings of the Boyal Society of Edinburgh. [Sess. 
XIV. — Notes on the Atmospheric Electrical Potential Gradient in 
the Industrial Districts around Leeds. By Dan. W. Steuart and 
Ingvar Jorgensen. Communicated by James A. S. Watson, B.Sc. 
(MS. received February 13, 1914. Read March 16, 1914.) 
The atmosphere of industrial districts is characterised by the pollution 
which it receives from smoke, comprising solid matters like carbon, tar, 
and mineral ash, and gaseous constituents such as S0 2 and C0 2 . 
Much work has now been done with regard to the ionisation of gases 
by various means.* Small ions, with a velocity of 1*6 cms. per second in 
an electric field of 1 volt per cm., have long been known to exist in the 
atmosphere. About ten years ago Langevin,f working in Paris, demonstrated 
the presence of large ions in addition, velocity 1/3000 cm. per second. 
M'Clelland and Kennedy J described the formation of large ions in the 
products of combustion, and later Kennedy, § comparing town and country 
air, found in town air (Dublin) a larger number of ions, due to combustion 
processes ; the large ions being increased, and to some extent at the expense 
of the small ones. Aitken [| has shown that the various products of 
combustion include nuclei of condensation and of spontaneous condensa- 
tion, due largely to the presence of sulphur in the fuel. As the envelope 
which transforms small into large ions often consists of water, these two 
sets of results may be correlated to some extent. Eve,H for example, 
concluded that dust, smoke, or mist in air causes a transformation of small 
into large ions. Several sizes of ions are now known to exist in air, 
commencing with the small ions and with decreasing velocities as the 
size increases.** 
The foregoing researches indicate that ionisation by combustion and 
the presence of combustion products in the air may be essential factors in 
the phenomena of atmospheric electricity in industrial districts. 
The following notes deal with measurements of potential gradients 
* J. J. Thomson, Conduction of Electricity through Gases. H. A. Wilson, Electrical 
Properties of Flames and Incandescent Solids , 1912. 
t Comptes Rendus, 1905, p. 233. 
J Proc. Roy. Irish Acad., 1912, xxx., A, No. 5. 
§ Proc. Roy. Irish Acad., 1913, xxxii., A, No. 1. 
|| These Proceedings , 1912, xxxii., Part 2, No. 16, and earlier. 
IT Phil. Mag., ccxxxv. p. 257. 
** Cf. Sutherland, Phil. Mag., 1909, p. 341. 
