July 29, 1920] 



NATURE 



689 



figured. A few fresh-water forms were met with, 

 including a new species of Physa, which is of interest 

 as being the most northern species of the genus. 

 Still, it should be noted that the closely allied Aplexia 

 hypnorum, of circumpolar distribution, occurs with it. 

 The Limnaeas proved extremely puzzling, and Dr. 

 Dall is inclined to consider that both the form known 

 as caper ata, Say, and the vahli of Beck may be only 

 boreal mutations of the well-known Limnaea palus- 

 tris, Miiller. Full lists of all the species collected at 

 the several stations and from Pleistocene deposits are 

 also included in this important paper. 



Mr. W. Wybergh has brought forward evidence, 

 including that of marine mollusca, to show that the 

 coastal limestones of the Cape Province (Trans. Geol. 

 Soc. S. Africa, vol. xxii., p. 46, 1920) are by no 

 means entirely due to the cementation of recent dunes. 

 The well-known dune limestone seems to have been 

 formed over and against a more ordinary and shelly 

 marine limestone, which constitutes the true Bredas- 

 dorp formation, and is of late Pliocene or Pleistocene 

 age. 



Papers on the Crown Colony of Sierra Leone are 

 comparatively rare. Mr. F, Dixey (Trans. Geol. Soc. 

 S. Africa, vol. xxii., p. 112, 1920) describes evidences 

 of Pleistocene movements of elevation, with the 

 formation of a coastal plain along nearly the whole 

 coast of the peninsula or Colony proper, merging on 

 the east into low ground that extends far into the 

 Protectorate. Parallel raised beaches show that the 

 uplift was intermittent. The highest beach is some 

 300 ft. above the sea. Four photographic views 

 accompany the paper. 



The question of the persistence of genera is raised 

 by Dr. C. D. Walcott in describing a remarkable 

 series of floating cyanophyceous algae from the 

 Middle Cambrian Burgess Shale of British Columbia 

 (Smithsonian Miscell. Coll., vol. Ixvii., No. 5, 1919). 

 Morania, one of his new genera, so closely anticipates 

 the structure of the modern Nostoc that only a feeling 

 that they cannot have been fully identical leads the 

 author to propose a new generic name. The illus- 

 trations are presumably from photographs of speci- 

 mens coloured by hand before reproduction ; but they 

 are, to say fTie least, surprising. 



Mr. Louis Renouf, of the Bute Museum, Rothesay, 

 writing in the Museums Journal for April-May on 

 various technical methods, including the mounting of 

 wet specimens under watch-glasses and petri dishes, 

 remarks on the difficulty of obtaining such glasses 

 with even edges, and nicely finished plates on which 

 tp mount them. The difficulty led to the discovery 

 that there was " no glass-planing plant in the whole 

 of Great Britain." If this be so, the discovery 

 accounts for a good deal that scientific workers have 

 had to contend with in obtaining glass apparatus (at 

 whatever price) from British firms. 



"The Rainfall in the Island of Formosa " has re- 

 cently been issued by the Government-General of For- 

 mosa, with a summary of meteorological observations 

 at Taihoku and five other observatories. Since the 

 NO. 2648, VOL. 105] 



meteorological service was established in 1896 rain- 

 fall stations have been added as available from 

 year to year. There were only 28 at the end of 

 1903, and there are now 135. Every 106 square miles 

 of Formosa has, on the average, one station. Most 

 of them are attached to various Government Depart- 

 ments. At 83 out of the 135 stations records are 

 available for ten years or more. The average annual 

 rainfall over the island is 2486 mm., the greatest 

 fall, 7176 mm., being at Kashoryo, situated on a 

 mountain slope at the head of a valley open to the 

 north-east a few miles south of Kelung; this spot is 

 said to be probably the most rainy in the Far East. 

 The minimum annual rainfall for Formosa is 1050 mm. 

 at Rochikuto, in Taichu, on the west coast. There are 

 two rainy seasons, one during winter along the extreme 

 north coast associated with the north-east monsoon, the 

 other in summer on the mountain districts in South 

 Formosa, largely due to typhoons and thunderstorms. 

 Typhoons occasion a considerable variation in the 

 rainfall according to their track and proximity, the 

 track being usually from south-east to north-west. 

 The heaviest rainfall in twenty-four hours in 

 Formosa is given as 1034 mni. at Funkiko on 

 .\ugust 31, iqii, which is the same day as that of the 

 flood in Taihoku shown in the frontispiece of the 

 publication under notice. The heaviest of the exces- 

 sive rains in different parts of the world, quoted for 

 comparison, are Charra Ponjee, India, 1036 mm., 

 June 14, 1876, and Baguio, Philippines, 1168 mm., 

 July 14, 191 1. Comprehensive tables and maps are 

 given showing the monthly and seasonal mean rain- 

 fall and the number of rainy days, also the five-day 

 mean rainfall at six observatories from the results for 

 twenty-two years, and the diurnal range, intensity' 

 and duration of rain. 



We have received copies of the second biennial Hurter 

 and Driffield memorial lecture delivered by Prof. Alex. 

 Findlay before the Royal Photographic Society on 

 May II, and the Hurter memorial lecture recently 

 delivered by Mr. F. F. Renwick before the Liverpool 

 Section of the Society of Chemical IndustrA^ Prof. 

 Findlav discoursed on the properties of colloids in 

 general, and especially with reference to photographic 

 processes and materials. He says : " In the produc- 

 tion of the photographic plate, . . . from the 

 moment of mixing the solutions to the final stage of 

 ripening of the emulsion, we have a complex series of 

 changes taking place in a delicately balanced and 

 complex colloidal system, in which coagulation, 

 peptisation, solution, and adsorption doubtless all take 

 part. . . In the production of the latent image 

 ... it seems probable that we are again dealing 

 with phenomena of adsorption." Mr. Renwick deals 

 with three characteristics of the latent image : 

 "(i) The p>ossibility of physically developing an image 

 on a fixed and washed plate; {2) the possibility of 

 transferring and subsequently developing (both 

 physically and chemically) latent images from the 

 silver salt in which they are formed to another, by 

 changing the former chemically into a less soluble 

 silver salt; and (3) the destructibility of the latent 

 image by the further action of light itself under 

 certain conditions." He gives the details of some 



