76 



NATURE 



[May 20, 1920 



In the other system of vibration the bar has a nodal 

 line running along the longitudinal centre of the bar, 

 while cross-nodes are also present; this class of vibra- 

 tion is termed a iu^ai system. In the latter we 

 may picture the sections of the bar on opposite sides 

 ■of the central line to be out of phase with each 

 other, so that one section is going upwards at the 

 moment the other section is going downwards. This 

 will give a slight rocking motion to the clamp, causing 

 the tree end of the needle to move to and fro in 

 -direction across the bar. Similarly, the bar is 

 vibrating between the cross-nodes, so we may picture 

 the sections divided by these to be upwards on one 

 side of the cross-node and downwards on the other, 

 thus giving a rocking motion to the needle in a 

 direction lengthwise with the bar. These two motions 

 (dual) combine to give the free end of the needle an 

 elliptical motion; hence the rotation of the spinner. 



The Hon. Sir Charles Parsons: Water-hammer 

 cone demonstrating the destructive eifect of col- 

 lapsing vortex cavities. The apparatus consists of a 

 hollow cone. At the small end is fitted a die-cap 

 through which passes a hole of the sanie diameter as 

 the small end of the cone. Between this cap and the 

 cone thin metal plates are inserted. The cone is 

 placed in water in the tank, allowed to fill with 

 water, and then thrust quickly downwards, its mouth 

 striking on to a rubber block at the bottom. The 

 sudden arrest by the rubber block gives a high rate 

 of relative acceleration of the water in the cone, pro- 

 ducing momentarily a cavity at the apex, which, how- 

 ever, immediately closes again with a perceptible 

 metallic hammering sound, and with sufficient pres- 

 sure, due to the concentrated energy of the closing 

 cavity at the apex, to puncture metal plates above 

 003 in. in thickness, indicating a pressure of 140 tons 

 per square inch. 



Mr. Edwin Edser : The concentration of minerals 

 and coal by froth flotation. Many valuable minerals, 

 particularly metallic sulphides, can be concentrated 

 from low-grade ores by crushing these to a fine 

 powder, mixing them with water, adding a small 

 quantity of a suitable reagent, and agitating the mix- 

 ture so that air is entrained in the form of fine 

 bubbles. On allowing the mixture to come to rest, 

 the bubbles carrying the mineral particles rise to the 

 surface, and find a mineralised froth which can be 

 removed. The barren rock (gangue) is not floated. 

 Demonstrations were given of (i) the recovery of 

 galena (lead sulphide) and blende (zinc sulphide) as 

 separate products from Broken Hill ore ; (2) the 

 recovery of coal from waste dumps. 



Sir Robert Robertson: Instrument for determining 

 the pressure developed by detonators by Hopkinson's 

 principle. This instrument, which was designed by 

 Mr. H. Quinney at the Research Department, Wool- 

 wich, illustrated the quantitative measurement of the 

 pressure of the blow delivered by a detonator accord- 

 ing to the principle enunciated by Hopkinson. This 

 principle depends on the separation of momentum into 

 pressure and time. When the blow is applied to one 

 end of a steel bar, a short length of the bar, attached 

 bv means of a faced joint to the other end, is thrown 

 off as a result of the application of the pressure of 

 the blow. The momentum of this short length (the 

 "timepiece ") is measured by catching it up in a ball- 

 istic pendulum. As the rate of transmission of the im- 

 pulse in steel is known, the time taken for the pres- 

 sure-wave to pass twice the length of the "timepiece " 

 is also known, and so the pressure can be deduced. 



Prof. F. W. Burstall: Optic indicator for internal- 

 combustion engines. An instrument for obtaining 

 the power and the pressure in internal-combustion 

 engines. The objects aimed at are to obtain accurate 

 readings of the pressures up to 600 lb. per square 

 inch and speeds up to 2500 revolutions per minute. 

 NO. 2638, VOL. 105] 



University and Educational Intelligence. 



Cambridge. — Mr. E. A. Milne, fellow of Trinii 

 College, has been appointed assistant-director of th< 

 Solar Physics Observatory. 



The new professorship of physical chemistry is 

 declared vacant. 



It is proposed to make it possible for students to 

 take the first M.B. examination before coming into 

 residence on account of the greater facilities now 

 provided in schools for the teaching of chemistry, 

 physics, and biology. 



The discussion on the syndicate's report on the 

 relation of women to the University is fixed for 

 October 14. 



The Local Lectures Summer Meeting will be held 

 from July 29 to August 18. The main subject of 

 study will be the history, literature, and art of 

 Spain, but courses in physical science (historical and 

 biographical) and in elementary astronomy are being 

 arranged in co-operation with the Association of 

 Science Teachers. Further information can be ob- 

 tained from the Rev. Dr. Cranage, Syndicate 

 Buildings, Cambridge. 



Liverpool. — Dr. Charles Walker has been ap- 

 pointed assbciate-professor in cytology and lecturer in 

 histology. 



Mr. J. Wemyss Anderson, dean of the faculty of 

 engineering, and associate-professor of engineering in 

 the University, has been appointed to the recently 

 established John William Hughes chair of engineering- 

 refrigeration. 



Messrs. Alfred Holt and Co., Ltd., of Liverpool, 

 have contributed 15,000^. to the University Appeal 

 Fund. The Association of West African Merchants 

 and the African Section of the Chamber of Commerce, 

 Liverpool, have decided to raise 12,000?. by voluntan.- 

 contributions from their members to provide a chair of 

 Colonial commerce, administration, and history at the 

 University and to increase the endowments of the 

 School of Tropical Medicine. 



London. — The following courses of advanced lec- 

 tures will begin shortly: — Three lectures on "The 

 Early Civilisation of Malta," by Prof. Th. Zammit 

 (of the University of Malta), at L'niversity College, 

 at 5.30 p.m., on' May 20, 27, and 28; four public 

 lectures on "High-frequency Alternators for Radio- 

 Telegraphy," at the Institution of Civil Engineers, 

 S.W.I, by M, Marius Latour (of Paris), at 5.30 p.m., 

 on May '26, 27, 28, and 31; and four lectures (in 

 French) on " Divers Modes de Dynamisme des Erup- 

 tions Volcaniques et les Phenomenes de Lateritisa- 

 tion," at the Imperial College (Royal School of 

 Mines), by Prof. A. Lacroix, at 5 p.m., on June 14, 

 15, 16, and 17. Admission to the courses is free, 

 without ticket. 



Announcement is made of the impending retirement 

 of Mr. T. P. Gill, who has been Secretary of the 

 Department of Agriculture and Technical Instruction 

 for Ireland since it was established. 



The Regional Association, in co-operation with the 

 Civic Education League, proposes to hold a meeting 

 at Glastonbury from August 21 to September 11. 

 The purpose of the meeting will be (i) to make a 

 regional 'survey, rural and civic, of Glastonbury and 

 its surroundings, and (2) to proceed, from the material 

 so obtained, to a critical study of social life and 

 institutions. Particulars may be obtained from Mrs. 

 Fraser-Davis, hon. secretary of the Regional Associa- 

 tion. lA Lancaster Place, Belsize Place, N.W.3, or 

 65 Belgrave Road, S.W.i. 



