November i r, 1922] 



NA TURE 



647 



islands are usually almost pure colonies of one species, 

 as the islands of Typha japonica or Zizania aquatica. 

 Another type of island consists mainly of one species 

 of a free-floating plant, such as the islands of Eich- 

 horiria crassipes. A very interesting case is reported 

 by Nakano from the shallow lakes found in high 

 moorland regions. Here masses of peat, crowned 

 with vegetation, may be raised from the bottom of 

 the lake in large part by the gaseous products accumu- 

 lated from decomposition processes, in part by the 

 buoyancy of the tissues of the living plants ; such 

 islands may be recurrent, sinking and rising in different 

 seasons. Floating islands are gradually leached of 

 any humus or mineral nutriment they may originally 

 possess, so that their base is ultimately mainly a 

 tangle of roots and fibre. It is to this cause that 

 Nakano traces the gradual disappearance of some of 

 the colonists prominent on the newly formed islands, 

 such as Pliragmites longivalvis, not as Pallis has 

 suggested for the " Plav " on the waters of the 

 Danube (Journal of the Linnean Soc, vol 43, 1916) 

 to the degeneration of a vegetatively propagated 

 plant. 



New Maps of the Gold Coast. — The Survey- 

 Department of the Gold Coast, which was closed 

 during the war, was reopened in 1920 under Lieut. - 

 Col. R. H. Rowe. Work has been pushed forward so 

 rapidly that about 15,000 sq. miles have now been 

 surveyed and the publication of the maps has begun. 

 The sheets, which are printed by Messrs. W. and A. 

 K. Johnston, are on a scale of 1 : 125,000. Relief 

 is shown by brown form lines at an interval of 50 feet. 

 Water features and names are in blue. Green is used 

 for forests, and various symbols are employed to show 

 the different kinds of plantations. Seven classes of 

 roads and tracks are shown. Soundings in coastal 

 waters are given in fathoms. The Accra sheet which 

 has just been published is an excellent piece of work, 

 and is notable both for its clarity and amount of 

 detail. The same publishers have also produced a 

 folding-map (scale 1 : 1,000,000) of the Gold Coast, 

 Ashanti, Northern Territories, and British Togoland. 

 No relief is shown. Colour is used for provincial and 

 other boundaries, water features, and motor roads. 

 This is a less striking map, but should prove useful 

 for general reference purposes. 



Tropical Cyclones in Southern Hemisphere. — 

 A summary of tropical cyclones in the South Pacific, 

 Australia, "and the South Indian Ocean, by Dr. S. S. 

 Visher, is given in the U.S. Monthly Weather Review 

 for June. For the South Pacific 246 hurricanes are 

 discussed. The huricane season extends from 

 December to April, and during this period about 95 

 per cent, of the recorded storms have occurred ; 

 January alone has 30 per cent., while the six months 

 from May to October make up only 4 per cent, of the 

 total. A table gives the frequency of occurrence in 

 the several island groups. A second table shows the 

 number of hurricanes between the longitudes 160 E. 

 and 140" W. for the several months and years, 

 consecutively for the years 1830 to 1922. There is 

 a further table which gives approximately the region 

 of the origin of cyclones in the South Pacific, which 

 shows a prevailing majority between 15 and 20 

 south latitude. Similar tables are given for recorded 

 hurricanes, between ioo° and 160° E., for Australia 

 and adjacent waters. The maximum number of the 

 approximate origins or places of first record occurs 

 between io° and 15° S. The main season for the 

 Australian hurricanes is from December to April, and 

 during this period about five-sixths of the storms 

 occur. Storms are rare from May to November. Of 

 the tropical storms in the South Indian Ocean, both 



NO. 2767, VOL. I to] 



January and February have 25 per cent, each and 

 March 20 per cent, of the total. Storms are extremely 

 rare from June to September. On the average rather 

 more than a dozen tropical cyclones occur annually 

 in longitudes 40 to ioo° E. There is generally a 

 preponderance of storms during recent years in the 

 three regions, doubtless due to an increased number 

 of observations. Representative tracks are well 

 illustrated on two charts. The author states that 

 many widely accepted generalisations as to tropical 

 cyclones appear unsafe in the light of fuller data being 

 gathered. 



Treatment of Tin and Tungsten Ores. — The 

 Tin and Tungsten Research Board, under the chair- 

 manship of Sir T. Kirke Rose, has recently given 

 an account of the work done during the period 

 January 1918 to December 1920, when its activities 

 came to an end (Department of Scientific and 

 Industrial Research. Report of the Tin and Tungsten 

 Research Board. Pp. vi+100. London: H.M. 

 Stationery Office, 1922. 3s. 6d. net.). As a useful 

 introduction to the papers dealing with the various 

 investigations that have been carried out, an account 

 is given by F. H. Michell of the methods already in 

 use for dressing tin ore in Cornwall, and E. H. Davison 

 gives a report on the microscopic examination of 

 veinstones. The ore-dressing investigations include 

 work on flocculation-effects and friability tests by 

 S. J. Truscott and A. Yates, and an investigation 

 by H. S. Hatfield of various physical properties in 

 relation to concentration possibilities. Hatfield found 

 that the osmose process was inapplicable to the 

 separation of cassiterite. He also found that there 

 is little prospect of increasing the yield on the dressing 

 floors by the addition of flocculating agents to the 

 pulp. His work on dielectric constants as a basis 

 of separation is novel and interesting, depending as 

 it does on a property which, like magnetic permeability, 

 is characteristic of the whole mass of a mineral 

 particle and not merely its surface, and is applicable 

 to minerals generally. Other researches, by Sir 

 T. Kirke Rose, J. H. Goodchild, and others, deal 

 with chemical and metallurgical methods, including 

 the use of solvents to remove cassiterite or wolfram 

 by direct solution, the conversion of cassiterite or 

 wolfram by furnace methods into a soluble product, 

 followed bv leaching, and the removal of the tin or 

 wolfram from ores by volatilisation, followed by 

 condensation. The report thus deals with many 

 aspects of ore-treatment. It gives a large amount 

 of information which will doubtless receive due 

 attention by those interested in the Cornish tin- 

 mining industry, and will presumably be put to 

 the test so far as is practicable when the mines 

 re-open. 



Separation of Isotopes of Chlorine. — In the 

 Memoirs of the College of Science of Kyoto Imperial 

 University, vol. iv., No. 7 (March 1921), Dr. Ishino 

 describes experiments with the crossed deflection 

 positive ray method, in which a separation of chlorine 

 into isotopes was obtained. The paper was received 

 on July 22, 1920, and the work was completed in 

 September 1919. Dr. Ishino made experiments to see 

 if the separation of the parabolas (which are clearly 

 shown in the plates) was due to impurities, and was 

 able to show that this was not the case. He found 

 the atomic weights of the two isotopes to be 34 and 

 36 ; a line, 37, was due to hydrochloric acid ; the 

 other hydride (35) had no corresponding line, but the 

 broadening of the line 37 seems to show the exist- 

 ence of such a hydride. The connexion with the 

 "whole number rule" and the helium nucleus is 

 pointed out. 



