RECENT ADVANCES IN SCIENCE 205 



variations. There are very few cases where the total life of 

 the storm amounts to an hour, or where the distance traversed 

 is as much as 100 kilometres. 



All the remaining part of the book, with the exception of 

 the last chapter, which gives a brief summary of current 

 theories regarding the origin of tornadoes, is devoted to a 

 very detailed discussion of the appearance of the tornado 

 cloud in all its stages, and of the wind and weather in its neigh- 

 bourhood. Of especial interest is the discussion (p. 104-6) 

 as to whether a tornado ever occurs without thunder and 

 lightning. The evidence shows that this happens very sel- 

 dom, if ever. The observations also suggest very strongly 

 that the funnel cloud does not depend from the central region 

 of the Cumulo-Nimbus cloud under which it forms, but from 

 the margin. There are numerous cases where it forms between 

 two neighbouring thunderstorms, but this is by no means a 

 necessary condition for its formation. The surrounding winds 

 are as a rule light, because the type of thunderstorm forming 

 in still and sultry weather more often gives rise to a tornado 

 than does the type which accompanies cyclonic depressions. 



Investigations on Lightning Discharges. — The Sixth Annual 

 Report of the University of Cambridge Solar Physics Observa- 

 tory contains, under the section for Meteorological Physics, 

 an account of important investigations on lightning discharges 

 by C. T. R. Wilson. There is evidence in support of the 

 theory that most positive discharges take place between the 

 earth and the negatively-charged upper portions of a cloud, 

 while a negative discharge is, as a rule, between the earth and 

 the lower positively-charged part. The energy dissipated in 

 an average flash is calculated to be between io 9 and io 10 joules. 



Rainfall in England : The True Long-Average as Deduced 

 from Symmetry. By Alfred A. Barnes, A.M.I.C.E. (Quart. 

 Journal Royal Met. Soc, July 1919). 



The Secular Variation of Rainfall. — By C. E. P. Brooks, 

 M.Sc. (Quart. Journal Royal Met. Soc, July 191 9). 



Two new cloud atlases have been published : 



Le Nubi (Rome, 191 7). — An Italian official publication. 



Naval Meteorological Cloud Atlas. — Published and issued by 

 the Hydrographer of the Navy, London, S. W. 



The first of these is photographic, while the second is illus- 

 trated by oil paintings by G. A. Clarke, of Aberdeen. 



