536 



NATURE 



[June 23, 1921 



The Second Royal Society Conversazione. 



THE second Royal Society conversazione of this 

 year was held at Burlington House on June 15, 

 when Prof. C. Sherrington received the fellows and 

 guests. 



Some of the exhibits had been displayed at the first 

 conversazione and were described in Nature of 

 May 191 p- 377; others were new, and the fol- 

 lowing brief descriptions have been taken from the 

 descriptive catalogue. 



Sir John Dewrance and Prof. K. G. Coker : Ap- 

 paratus for investigating the action of cutting tools 

 by polarised light. A transparent disc is turned at a 

 slow speed b\ an electric motor through a worm 

 reduction gear, and the cutting tool of glass or other 

 material is clamped in a slide rest and receives a 

 determinate radial feed from the main drive The 

 mode of action of various forms of cutting tools is 

 observed in polarised light, and the stress distribu- 

 tions in both work and tool are investigated by this 

 latter means. 



Mr. R. N. Chrystal (Forestry Commission): An 

 insect enemy of the Douglas fir recently introduced 

 frorn America, Chermes Cooleyi, Gill. This insect 

 may prove a serious enemy of our two most important 

 exotic conifers, the Douglas fir and the Sitka 5;pruce. 



Mr. Percy J. Neate : Recording extensom<?ter for 

 textile yarns, etc. The specimen is secured vertically 

 between an upper grip attached to a spring and a 

 slowlv descending lower grip. The movement of the 

 lower grip is therefore the sum of the extensions of 

 spring and specimen. This movement is halved and 

 transmitted to a platen travelling downwards at an 

 angle of 60° to the vertical. The spring is designed 

 for a scale of 12 o;;. = 3 in. ordinate, but is calibrated 

 to extend 3 x 2/ V'3 in. at that load. The combined effect 

 is to eliminate spring extension from the abscissae 

 and excess spring extension from the ordinate. 



Mr. William Barlow : The methods of chemical 

 graphic formulae modified so as to interpret crystal 

 structure by means of models. Certain partitionings 

 of space into similar cells embody the conception that 

 stable equilibrium of a crystal indicates the presence 

 of similarly situated centres of repulsion. In the case 

 of the diamond when regular dodecahedral cells are 

 emploved and four cells, forming a tetrahedral group, 

 are allotted to each atom, the symmetry traced by the 

 Braggs is presented by the group centres. The case 

 of benzene is found to be met if, while four cells 

 stand for each carbon atom, one is representative of 

 each hydrogen atom. Further investigation has re- 

 vealed the genera] principle that the allotment of the 

 rells among the atoms follows the fundamental 

 valencies ; thus a monovalent atf^m requires one cell, 

 a divalent two, a trivnlent three, and a carbon atom 

 four. In a lar^e number of cases an appropriate 

 partitioning;- into sim'lar unit-clls when fully allotted 

 on the principle just stated yields assemblages of cells 

 almost identical in symmetry and relative dimensions 

 with the corresponding crystals. • 



St'r Henry Howorlh : A Dutch house interior. A 

 /our de force in perspective, painted by De Hooge or 

 his pupil Hoogestratten, whose name occurs on a 

 representation of a letter on the table, probably for 

 exhibition at a Kermeez or Dutch fair. The late 

 Lord Kelvin and others were puzzled to know how 

 it was executed, since the picture is painted on three 

 planes ; since a different view is seen when looked at 

 from the holes at either end and there are no lenses 

 in the holes, it would be interesting to know how the 

 artist accommodated his drawing. 



Prof. R. C. Piinnett : Hen-feathered cocks. In 

 some breeds of poultry the cocks are feathered like 

 the hen, lacking the characteristic hackles and sickles 



NO. 2695, VOL. 1:07] 



of normal cocks. Experiments have shown that the 

 assumption of henny feathering by the cock is due 

 to a factor which behaves as a Mendelian dominant. 

 Castration of such birds leads to the assumption of 

 normal male plumage. Experiments by Goodale in 

 .America and Pezard in France have shown that the 

 castrated hen also develops cock feathering. It seems 

 probable that hens and henny cocks alike contain a 

 factor which inhibits the development of the normal 

 cock plumage. 



Royal Observatory , Greenu^ich : Astronomical photo- 

 graphs, (i) Four Franklin Adams chart plates in 

 frame. (2) Solar eclipse, 1919, May 29, showing; 

 prominence and corona. (3) Solar eclipse, 19 19, 

 May 29, showing surrounding stars. (4) Solar eclipse, 

 1921, April 8. (5) Sun-spots, 1921, May 13. 



The Rev. A. L. Cortie : Astronomical photographs 

 and drawings from Stonyhurst College Observatory, 

 (i) Bright-line spectra of Nova Cygni III., 1920. 

 August 29 and 30 and September 6. The great inten- 

 sity of Ha -is shown on the plate of August 30. 

 (2) The genesis of the great sun-spot group of 1920, 

 March 22-27. The drawings were the 'ast made by the 

 late Br. Wm. McKeon, S.J. They were reproduced 

 by him from drawings made at the telescope, and 

 show the development of the disturbance from 19 iq, 

 December 27. 



Dr. William Wilson : A new form of astronomical 

 model designed for educational purposes. The model, 

 while demonstrating the more familiar motions of the 

 sun, earth, and moon and the various phenomena 

 resulting therefrom, reproduces, in addition, the retro- 

 grade motion of the moon's orbital nodes (with its 

 svnodic revolution of 346 days) and the forward 

 motion of the moon's apsides (with its synodic revolu- 

 tion of 412 days), and is thus capable of affording 

 a demonstration of the Chaldean " Saros " or eclipse 

 cycle of 18 years and 11 days, with its 41 solar and 

 29 lunar eclipses, the dates on which these eclipses 

 will occur, and the further differentiation of them 

 into total and partial in the case of the moon, and 

 total, partial, and annular in the case of the sun. 



The Meteorological Office : Apparatus for record- 

 ing atmospheric pollution. Dr. Owens's automatic 

 air filter is an instrument which at the end of every 

 fifteen minutes automatically draws two litres of air 

 through a piece of fine blotting-paper. The darkness 

 of the circle of deposit left on the paper gives an 

 estimate of the amount of suspended matter in the 

 air. Records are shown illustrating the reduction 

 in the amount during the coal strike and the relative 

 importance of domestic fires and factories. The 

 amount of suspended matter is found to be closely 

 connected with the vertical electric force. The reduc- 

 tion in the latter at the end of a fog is illustrated by 

 a record taken at Kew. 



The National Physical Laboratory: (i) Patfrson- 

 Walsh electrical height-finder. Designed during the 

 war for measuring the height of enemv aircraft, it 

 depends on the Bennett-Plevdell "roof" principle of 

 height measurement. The' action of the _ electrical 

 height-finder is, by means of a sliding bar situated in 

 each sighting plalne and passing over a horizontal 

 uniform resistance, to obtain at each station a poten- 

 tial proportional to the contangent of the angle of 

 elevation at that station. These two potentials, com- 

 bined in series bv cables connecting tl:e two stations, 

 and operating r^cross a resistance proportional to B. 

 give a (urrent inversely proportional to the height, 

 and thus, a miUiammeter mav, by ma king it with an 

 inverse height-fxale, be made to gi e a continuous 

 indicaticn of the height of anv obje t on which the 

 two planes arc constantly sighted. (2) Photomicro- 



