Marcii 4, 1909J 



NATURE 



29 



the llae idt-ally representing the true image of the edge. 

 1 he object aimed at is to measure the actual intensity of 

 illumination in the image at different distances on either 

 side of this ideal line. The variation in the illumination 

 with the distance is, of course, very rapid, and the total 

 distance over which it is necessary to carry the measure- 

 ments is in general extremely small. To isolate the strip 

 parallel to the knife-edge, the illumination of which is to 

 be measured, a narrow slit is placed in the focal plane of 

 the microscope objective, and is thus magnified by the 

 eve-piece. To measure the intensity of the illumination 

 seen through this slit — i.e. the illumination along a line 

 parallel to the ideal iinage of the knife-edge — a special 

 mechanism is employed, whereby this image is made to 

 alternate with light from a constant source, which, how- 

 ever, can be varied in a measurable proportion, so as to 

 become of equal intensity with the illumination to be 

 measured. This equality is judged by the absence of 

 " flicker " when the alternations are made to succeed one 

 another with appropriate frequency. — Best conditions for 

 photographic enlargement of small solid objects : A. 

 Mallock. When it is desired to take an enlarged photo- 

 graph of an object which is not flat, and which cannot, 

 therefore, be in focus in all parts, the question arises as 

 to what form of lens should be used in order to secure the 

 best results. It is shown in the paper that if a certain 

 minimum fineness of definition is required, say, the separa- 

 tion of points the distance apart of which is a,, then, in 

 the first place, the lens used must be capable of resolving 

 points half this distance apart ; and, secondly, that the 

 greatest distance (b,) of the surface from the focal plane 

 must not exceed a/aa, where o is the angular aperture of 

 the lens. The resolving power of a lens being dependent 

 on o and the wave-length, it is shown that if a = n\, then 

 h = n-\\ nearly. The best that can be done, therefore, in 

 photographing a curved or uneven surface is to use a 

 lens which will resolve half the least distance to be defined 

 in the picture. If this be done, all points which are not 

 within a distance a, of one another, and not more than 

 ir^A out of focus, will appear separated in the picture. 

 On the other hand, if h is given, the least distance which 

 will be resolved over the whole picture is 2\/(fcX). 



Zoological Society. Fi-hruarv 16. — Mr. F. Gillelt, vice- 

 president, in the chair. — Fauna of the Cocos-Keeling Atoll : 

 Dr. F. Wood-Jones. The work was based on collections 

 made by the author during a stay of fifteen months in 

 1005 and iqo6, and in the case of most orders was believed 

 to he fairly complete. — The anatomy of certain Ungulata, 

 including Tapirus, Hyrax, and .Antilocapra : F. E. 

 Beddard. — Le Rhinoceros Blanc du Soudan {Rhinoceros 

 si))i ii.i lO/foiii'J : Dr. E. L. Trouessart. 



Institution of Mining and Metallurgy, February iS — 

 .Mr. .Alfred James, president, in the chair. — .Adjourned 

 discussion on a theory of volcanic action and ore deposits, 

 (heir nature and cause : Hiram W. Hixon. — The follow- 

 ing papers were also discussed : — .An instance of secondary 

 impoverishment : H. H. Knox. This paper dealt with 

 deposits on the private estates of Kishtim, in the govern- 

 ment of Perm, Russia, in which are occurrences of un- 

 tjsidised iron sulphides, which have been leached of their 

 copper contents. The mines particularly dealt with were 

 a group comprising the Tissoff, Koniukhoff, and Smirnoff 

 lodes in the Soimonorsk Valley. — " Shrinkage " sloping 

 in Western .Australia : F. Percy Rolfe. .A description of 

 the method of stoping used at the Lake View Consols 

 Gold Mine, and a review of the advantages and dis- 

 advantages of the method as compared with the common 

 system of stoping adopted in Western .Australia by means 

 of " mullock " or " filled " stopes. The reasons for 

 utilising " shrinkage " stoping in this particular mine were 

 stal.d. and the details of the' method fully explained. 



Paris. 

 Academy of Sciences. Helinia'v 22. — V. Emile Picanl in 

 the chair. — Hertzian waves and Fredholm's equation : H. 

 Poincare. It is shown that several problems relating to 

 Hertzian waves can be reduced to the integration of a 

 Fredholm's equation. — The sex in sea-urchins obtained by 

 NO. 2053, VOL. 80] 



experimenlal parthenogenesis: Vvos Delage. 'i wo sea- 

 urchins, which had survived their inetamorphosis sixteen 

 months, were accidentally killed by a change in their con- 

 ditions of life. The determination of their sex showed 

 that one was certainly, and the other probably, male. 

 From this the conclusion is drawn that sea-urchins pro- 

 duced by experimental parthenogenesis can be raised to the 

 adult state, characterised by the presence of the sexual 

 elements, and that males can be thus obtained. — Electrical 

 discharges in intense magnetic fields : .M. Gouy. — The 

 principles of intrinsic projective geometry : .A. Demoulin. 

 — Some figures determined by the infinitely near elements 

 of a skew curve : B. Hostinsky. — The application of the 

 generalised theorem of Jacobi to the problem of Jacobi- 

 Lie : W. Stekloff. — The search for roots of certain 

 numerical transcendental equations : R. de Montessus. 

 — The statical graphics of the aeroplane : L6on Lecornu. 

 — The force and power of propulsion of aerial helices : 

 Rene Arnoux. — The thermal effects of a musical arc ; the 

 probable fusion of carbon : M. La Rosa. The amount of 

 energy in a singing arc is much greater than in an 

 ordinary arc possessing self-induction, and hence should 

 possess a much higher temperature than the latter. By 

 the action of a singing arc on sugar charcoal masses ot 

 graphite have been obtained possessing such firmness and 

 tenacity as to suggest that the charcoal had been fused. 

 — The constitution of subterranean telephone circuits in 

 large towns : M. Devaux-Charbonnel. It has been 

 known for some time that the presence of an underground 

 section of a telephone circuit diminishes considerably the 

 intensity of the voice, and particularly affects the distinct- 

 ness of certain consonants. In the present paper a calcu- 

 lation is given showing the relation between a given length 

 of air line and the corresponding length of underground 

 cable. The most advantageous diameter of wire for the 

 cable is also worked out, and the important advantages 

 possessed by cables of small capacity indicated. — The exist- 

 ence of positive electrons in vacuum tubes : .A. Dufour. 

 The author has repeated the experiments of J. Becquerel 

 on the existence of positive electrons in vacuum tubes, and 

 has obtained the same experimental results. The author's 

 interpretation of the experiments is, however, different from 

 that given by M. Becquerel, and does not necessitate the 

 assumption of the existence of positive electrons in the 

 vacuum tube. — The atomic weight of potassium : G. D. 

 Hinrichs. The author applies his methods of calculation 

 to the recent data of V. Lenhcr, and concludes that the 

 true atomic weight of potassium is 39- 125. — The colour 

 reactions of indol bodies with sugars : Julius Gnezda. — 

 The chloralic acids : M. Hanriot. The substances 

 obtained by combining chloral with various sugars have 

 been submitted to oxidation : acids, which are called 

 ihloralic acids, are produced, the properties of a number 

 of which are .described. — Syntheses by means of the mixed 

 zinc organo-nietallic derivatives : E. Blaise and -A. 

 Koehler. This general method of svnthesis starts from 

 the ester-acids of the type CO,Et.(CH,)„.CO,H, details 

 being given of the best methods of preparing these acids. 

 These are then converted into the chlorides 



CO,Et.(CH.)„.CO.Cl, 

 and then submitted to the reaction represented by the 

 equation 

 CO.,Ec(CH.,i„COCI + I^.ZnI = ZnICi + CO.,Et(CH,)„.CO.R. 



Symmetrical diketones can also be obtained by a modifi- 

 cation of the conditions, and the properties of a number 

 of these are given.— The preparation of indazylic deriva- 

 tives by means of hydrazo-orthoketones : P. Carre. — 'I he 

 nature of the cyano-compounds of Kirsch : X. Rocques 

 and L. Levy. The hydrocyanic acid in Kirsch two or three 

 years old exists only partially in the free state, a part being 

 combined with fatty derivatives of high molecular weight. 

 —The coagulation of milk by the ferment of Cayica 

 papaya : C. Gerber. — Some new properties of the o.xydases 

 of liussula delica: J. Wolff. — The colloidal properties of 

 starch with respect to its chemical constitution : Eugene 

 Fouard. The rotatory power of a limpid solution of 

 starch, obtained by filtration through a collodion film, is 

 a function of the alkalinity of the liquid. .As the amount 

 of potash added is increased, the rotation lends to a limit 



