RECENT ADVANCES IN SCIENCE 201 



line. As an example of the practical results, a summary of 

 several sets of observations is given, which shows an average 

 error of position of only about 10 miles ; this accuracy is 

 amply sufficient for the practical purposes of aerial navi- 

 gation. 



The following are some of the more important papers 

 recently published : 



Lau, H. E., Beobachtungen des Planeten Mars (4th paper), Ast. Nach., 208, 



No. 4983, 19 19. 

 Chapman, S., Theories of Magnetic Storms, Observatory, 42, 196, 1919. 

 Hale, G. E., Ellerman, F., Nicholson, S. B., and Joy, A. H., The Magnetic 



Polarity of Sun-spots, Astroph. Journ., 49, 153, 1919. 

 Fowler, A., and Gregory, C. C. L., The Ultra-violet Band of Ammonia and its 



Occurrence in the Solar Spectrum, Trans. R. S., Ser. A, 218, 351, 191 8. 

 Carter, E., and King, A. S., A Further Study of Metallic Spectra produced in 



High Vacua, Astroph. Journ., 49, 224, 1919. 

 LUNT, J., The Spectra of Nova Aquilaa No. 3 : I, The Dark-line Spectrum, M.N., 



R.A.S., 76, 416, 1919. 

 Shapley, H., Studies based on the Colours and Magnitudes in Stellar Clusteis : 



XI, A Comparison of the Distances of Various Celestial Objects, Astroph. 

 Journ., 49, 249, 1919. 

 Slipher, V. M., On the General Auroral Illumination of the Sky and the Wave- 

 length of the Chief Aurora Line, Astroph. Journ., 49, 266, 1919. 

 Guthnick, P., Kiinstliche Lichtkurven, Ast. Nach., 209, No. 4993, 1919. 

 Smart, W. M., The Position Line in Navigation, M.N., R.A.S., 79, 520, 1919. 



METEOROLOGY. By E. V. Newnham, B.Sc, Meteorological Office, 

 London. 



Note on Tornadoes, by J. Logie. — This paper was read before 

 the Royal Meteorological Society on June 18, 1919, and will 

 appear shortly in the Quarterly Journal of that Society. 



The ordinary convectional theory attempts to explain the 

 very low pressure near the centre of a tornado in the following 

 way : Unequal heating of the ground causes a rising current 

 of warm air which is maintained at a temperature higher than 

 that of the surrounding air by means of the heat liberated by 

 the condensation of water vapour which is required for the 

 formation of the funnel cloud. Air moves in towards the 

 centre along a spiral track, and in accordance with the prin- 

 ciple of the conservation of angular momentum, acquires a very 

 great rotational velocity as it nears the centre. There is a 

 great reduction of pressure as a result of the centrifugal force 

 of the revolving air. The author comes to the conclusion that 

 the heat liberated by condensation of water vapour is not 

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