520 



NATURE 



[December i6, 1920 



instructive films of this kind for exhibition except by 

 applying to a number of different firms. The Mac- 

 millan Educational Film Co., Ltd., 32 Charing Cross, 

 S.W.I, has now, however, made a collection of educa- 

 tional and scientific films which they are able to 

 offer for hire. We have before us a list of such films 

 relating to geographical, industrial, Nature-study, and 

 other subjects, and a copy can be obtained by anyone 

 upon application to the company. There are also 

 lists of suggested programmes — one of a varied kind, 

 and another in which geographical subjects are appro- 

 priately grouped together. It may be hoped that local 

 education authorities will avail themselves of such 

 assistance as is afforded by these lists to give a new 

 character to kinematograph displays in local picture- 

 houses. In the United States thousands of schools 

 make use of the moving picture for educational pur- 

 poses, and there is a great opportunity for its wise 

 employment here when existing prejudices have been 

 overcome. 



Societies and Academies. 



Cambridge. 



Philosophical Society, November 22. — Prof. Seward, 

 president, in the chair. — F. A. Potts : A note on vital 

 staining. In studies which have been made on the 

 penetration of neutral red into the living body of the 

 soil nematode Diplogaster it is found that most of 

 the stain makes its v.ay through the mid-gut and 

 none through the skin. In the mid-gut a zone of 

 granules arranged peripherally round the lumen of the 

 gut takes up the stain particularly. — W. F. 

 Lanchester and A. G. Thacker : Preliminary note on 

 thq superior vena cava of the cat. Thirty cats were 

 dissected to observe the point of entrance of the 

 internal jugular, which in every case except one fell 

 into the external jugular. Observations were also 

 made on the length of the superior vena cava in 

 twenty-one adult cats, and the length appeared to be 

 varying round more than one mean. — Miss M. D. 

 Haviland : Preliminary note on a Cynipid hyper- 

 parasite of Aphides. Charips (Cynipidae) is a hyper- 

 parasite of -'Vphides through .'\phidius (Braconidae). 

 The female pierces the Aphidius larva while the latter 

 is Iving inside the living Aphid, and deposits an egg 

 within its body. The first-stage larva of the Cynipid 

 is hypermetamorphic, with a thick chitinous skin 

 and tail, but during development, which takes place 

 within the Aphidius, the larva gradually assumes the 

 form usual among parasitic Hymenoptera. Shortly 

 before metamorphosis the hyperparasite leaves its 

 host, the remains of which it devours, and its tracheal 

 system becomes functional. It afterwards pupates 

 within the cocoon previouslv woven bv the Braconid. 

 —Dr. E. H. Hankin and ' F. Handfey Page : The 

 problem of soaring flight (see p. 518).— Sir George 

 Greenhill and Dr. G. T. Bennett : The rotation of a 

 non-spinning gyrostat. — E. V. Appleton : A method 

 of testing triode vacuum tubes. A dynamic method of 

 measuring the slope of the _ principal voltage-current 

 characteristic of a three-electrode thermionic tube is 

 described. — ^W. B. Frankland : The astronomical bear- 

 ing of the Einstein theory.— Dr. W. Burnside : The 

 representation of the simple group of order 660 as a 

 group of linear substitutions on five symbols. Except 

 m the cases of two and of three variables, the 

 explicit forms of groups of linear substitutions have 

 been given only in a few cases. Thus it is hoped that 

 the explicit forms in the case referred to may be of 

 interest. The existence of a cubic three-spread, in 

 space of four dimensions, admitting a group of 



NO. 2668, VOL. 106] 



660 collineations into itself may be compared with 

 the more familiar case of Segre's cubic three-spread 

 which admits a group of 720 such collineations. 



Manchester. 

 Literary and Philosophical Society, November 2. — Sir 

 Henry k. Miers, president, in the chair. — Dr. W. J. 

 Walker : The polytropic curve and its relation to 

 thermodynam.ic efficiency (with a 'note on the theory 

 of the uniflow steam-engine). An inquiry made into 

 the reason for the diminution of internal^combustion 

 engine efficiencies when the value of n in the equa- 

 tion, /id" = constant, for the compression line is 

 reduced by water injection or other means. — W. H. 

 Pearson : Notes on a collection of Hepatics from the 

 Cameroons, West Coast of Africa. The collection, 

 made by Mr. W. G. Travis from logs of ebony in 

 the Liverpool docks, contained the following species : 

 Aneura Travisiana, n.sp.. Pears. ; Lophocolea New- 

 toni, St. ; Mastigolejeunea . . . ? ; Homalolejeunea 

 excavata (Mitt.), Sp. ; Ceratolejeanea Saxbyi, n.sp.. 

 Pears. ; and Cheilolejeunea Principensis, St. The type- 

 specimens are in the Manchester Museum. 



SlIEFFIKI.D. 



Faraday Society and Institute oi Metals (SheiBeld 

 Section), November 19. — Afternoon session. Prof. 

 C. H. Desch in the chair. — Dr. L. Aitchison : Electro- 

 plating for the prevention of corrosion. The paper 

 dealt more especially with the protection of iron and 

 steel and their alloys. The conditions for proper pro- 

 tective coatings were defined and the value of the 

 various protective coatings was discussed with relation 

 thereto. — W. A. Thain : Some applications of electro- 

 deposition in aeronautical engineering. Three cases 

 of the electro-deposition of copper were considered, 

 viz. : (i) .^s a protection against carburisation in case- 

 hardening practice ; (2) as a means of increasing heat 

 conductivity ; and (3) as a means of building up a 

 definite constructional detail. — B. Carr : The electro- 

 deposition of cobalt. From a bath containing 43 lb. 

 of cobalt sulphate crystals, 5J oz. of boric acid, and 

 25 oz. of sodium chloride per gallon, and used at 

 34° C, excellent hard, adherent deposits of cobalt 

 were obtained, provided that these were not too 

 thick, with 150 and 72 amperes per sq. ft. for 

 periods of immersion not exceeding 2 and 

 4 minutes respectively. The deposit is exceedingly 

 resistant to atmospheric corrosion, and superior to 

 nickel in the rapidltv of deposition and hardness. — 

 W. E. Hughes : The use of colloids in the electro- 

 deposition of metals. — S. Field : The commercial elec- 

 trolvsis of zinc sulphate solutions. Commercial elec- 

 trolysis aims at the maximum extraction of zinc with 

 a minimum of energv. The greater the extraction the 

 smaller the volume of liquor which circulates through 

 the extraction plant, and the smaller the proportion of 

 zinc which demands repeated purification. A limit to 

 this extraction is set by the cost of increased energy 

 necessary to take out zinc from dilute liquors. Cur- 

 rent efficiencv is dependent upon a number of factors, 

 including current density, amount of zinc present, 

 temperature, and the presence of impurities. 



Evening session, Mr. E. A. Smith in the chair. — 

 W. R. Barclay : Electro-silver plating and its 

 technical development. This paper dealt with the 

 history of technical investigation and research into the 

 electro-deposition of silver so far as the more practical 

 aspect of electro-plating is concerned. Emphasis was 

 laid on the necessitv for careful co-ordination of the 

 factors of metal and free cyanide content to that of 

 current density. It vi^as shown that though con- 

 siderable latitude is allowable in practice, the best 

 results and highest efficiencv lie within fairly w'ell 



