^20 



NATURE 



[July 25, 1901 



SOCIETIES AND ACADEMIES. 



London. 



Royal Microscopical Society, June" 19,— Mr. William 

 Carruthers, F. R.S., president, in the chair. — Mr. T. H. Powell 

 exhibited Coscinodisciis asteromphalus under a new i/40thinch 

 apochromatic oil immersion objective. — Mr. J. \V. Gordon read 

 a paper entitled " An examination of the Abbe diftVaction theory 

 of the microscope," in which he stated that the above long- 

 accepted explanation of the phenomena of high- power micro- 

 scopic observation had been accepted on insufficient proof and 

 would not bear the test of critical examination. The Abbe 

 theory claimed that pictures formed by the microscope of very 

 minute objects were due to diffraction images originated by the 

 object, and that when the oblique rays of light in which these 

 diffraction images existed were excluded, no image of the object 

 was possible. This theory had been experimentally illustrated 

 by Prof. Abbe by means of a grating on the stage of the micro- 

 scope and a series of diaphragms behind the microscope object 

 glass with slits to partially exclude oblique rays. Mr. Gordon 

 showed that although in favourable circumstances diffraction 

 effects were produced by fine objects on the st.age of the micro- 

 scope, these effects did not appreciably influence the formation 

 of the image. He also showed that the experimental results 

 produced by the above-mentioned diaphragms, which were 

 adduced to prove the theory, were due to a diffraction effect 

 produced by the diaphragms themselves and not by the grating 

 on the stage of the microscope, the same results being ob- 

 tained with an aiirial image of a grating projected upon the 

 stage by a lens in place of the actual grating. He maintained 

 that in the microscope, as in the telescope, it was necessary to 

 eliminate diffraction effects as far as possible by making lenses 

 of large aperture, and not, as in Abbe's theory, to include as 

 many diffraction phenomena as possible. Diagrams in illustra- 

 tion of the paper were thrown upon the screen, and the various 

 experiments referred to were exhibited under a number of 

 microscopes. In the discussion that followed. Prof. S. P. 

 Thompson agreed with Mr. Gordon in rejecting the presentation 

 of the Abbe theory given by Naegeli and Schwendener, but 

 found himself at variance with Mr. Gordon on almost every 

 other point, and proceeded to discuss several conclusions arrived 

 at in the paper. 



Paris. 



Academy of Sciences, July 15. — M. Fouaue in the 

 chair. — Determination of three principal optical parameters of a 

 crystal, in magnitude and direction, by the refractometer, by 

 M. A. Cornu. Though the measurement of the three principal 

 indices of a crystal is relatively easy, the determination of the 

 three principal directions involves calculations too intricate for 

 ordinary work. A geometrical study of the total reflection at a 

 crystalline surface has led the author to some analytical relations 

 upon this application of the refractometer, of unexpected sim- 

 plicity. Numerous observations of crystals with an .-^bbe refrac- 

 tometer have shown that the formula; developed are exact 

 within the limits of error of the experimental results. Large 

 clinorhombic crystals of commercial tartaric acid have been used 

 in the experiments to test the formula-. The demonstration of 

 the formula; and the numerical results are reserved for a future 

 communication. — On the morphology and position of flagellated 

 parasites with undulating membrane, by MM. -A.. Laveran 

 and F. Mesnil. The characteristics of organisms of the two 

 genera Trypanosoma and Trichomonas are described and 

 compared, and the distinctive features are defined. The 

 former genus comprises all the flagellated parasites which 

 have been found in the blood of vertebrates. — Can poisoning 

 be caused, through the skin and mucous membrane, in a 

 medium which has been rendered irrespirable by sulphuretted 

 hydrogen ? by M. A. Chauveau. Experiments with dogs have 

 shown that, provided an inhaling apparatus is worn upon the 

 head, no ill effects ensue, even if the body of the animal is in 

 an atmosphere charged with sulphuretted hydrogen so as to be 

 poisonous. —On the sugars from blood, by MM. R Lepine and 

 Boulud. In the blood of dogs fed upon meat, or fasting, a sugar 

 has been found analogous to saccharose, but differing from it in 

 some properties. — On a new joint with variable angle, by M. G. 

 Koenigs. — On the extension of the Riemann method of inte- 

 gration, by M. J. Coulon. — On the solution of equations of 

 elasticity, in the case where the values of the unknowns at the 

 limit are known, by M^L Eugene and F. Cosserat. — On 



NO, 1656, VOL. 64] 



the movement of a pendulum in a resisting medium, by M. L. 

 Decombe.— On the changes of phase produced in incident rays 

 'n the neighbourhood of total reflection, but lower than the limit- 

 ng angle, by M. J. Mace de Lepinay. — Measures of wave-length 

 n the solar spectrum ; comparison with Rowland's scale, by 

 M. Perot and C. Farry. Thirty-three lines in the solar spectrum 

 have been compared directly with the green light of cadmium, 

 and the wave-lengths have been plotted. The observations 

 suggest that Rowland's scale of wave-lengths is not perfect, 

 and indicate where corrections might be made. — On the direction 

 of magnetisation in beds of clay transformed into hard brick 

 by layers of lava, by MM. B. Brunhes and P. David. It is 

 known that clay baked in a furnace acquires magnetisation in the 

 direction of the terrestrial magnetic field at the time when it is 

 transformed into the condition of brick. The authors have exam- 

 ined some beds of hardened clay covered with lava near Clermont, 

 in the Auvergne district, with the idea of finding the magnetic 

 condition. It appears that in general the magnetic condition 

 of the beds is decidedly different from that of the neighbour- 

 hood, and the dift'erence is taken to indicate the change which 

 has occurred since the epoch when the clay was baked by the 

 lava flow. — Thermal study of potassium hydrates, by ftl. de 

 Forcrand. The observations indicate that in addition to the 

 two compounds KOH and KOH-h2H.iO there are two other 

 intermediate hydrates, viz. KOH-ho-5H.,0 and KOH-fH^O. 

 — On some derived phenyl ether compounds, by M. P. Brenans. 

 The author describes some ether-oxides and ether salts of 

 diiodophenol and triiodophenol. — Action of pyridine bases on 

 tetra-chloro-benzo-quinones, by M. Henri Imbert. — New re- 

 actions with <-butyrylacetylacetate of methyl, by M. A. Haller. 

 — On pyromucic and isopyromucic acids, by M. Chavanne. — 

 Contribution to the study of ortho-xylene bichloride, by ^L L. 

 Ferrand. — Precautions to be taken in the study of partheno- 

 genesis in sea-urchins, by M. C. Viguier — Germination of the 

 spores of Pencillium in humid air, by M. P. Lepage. — Formation 

 of layers of ice, in summer, in the volcanoes of Auvergne, by 

 M. P. Glangeaud. — Action of currents of high frequency and 

 tension on urinary secretion, by MM. Denoyes, Martes and 

 Rouviere. — Observations of a meteor at Floirac (Gironde) on 

 July 5, by M. E. Esclangon. — On the action of the electric 

 current on microbes, by MM. Apostoli and Laquerricre. 



CONTENTS. PAGE 



Another Book on British Birds, By W. P. P. . . 297 

 Practical Phys'ology. By Benjamin Moore . . . 29S 



An American Introduction to Botany 300 



Our Book Shelf:— 



Schunichen und Kalberlah : " B Eyferth's Einfachste 

 Lebensformen des Tier- und Pflanzenreiches. 

 Naturgeschichte der mikroskopischen Stisswasser- 



bewohner."— C. S. West 301 



" Handbook of British, Continental and Canadian 

 Universities, with special mention of the Courses 



open to Women " 3°' 



Letters to the Editor : — 



The Subjective Lowering of Pitch. — Prof. F. J. 



Allen 301 



Phototherapy.— M. H. Close 301 



The Congress on Tuberculosis 301 



The Liquefaction of Hydrogen. (Illustrated.) . . 302 



Professor Tait. By Prof G. Chrystal 305 



Notes 307 



Our Astronomical Column : — 



The Total Solar Eclipse, May iS, 1901 31 1 



The Twelve Movements of the Earth 312 



New Nebuhi; 3'2 



The Suppression of Tuberculosis. By Prof. 



Robert Koch . . 312 



The Royal Horticultural Society's Lily Conference. 



By Wilfred Mark Webb 316 



The Properties of Steel Castings {Illustrated.) . . 316 



Scientific Work in Egypt 317 



University and Educational Intelligence 319 



Societies and Academies 3^*^ 



