June 14, 19 17] 



NATURE 



Z^7 



Canidse family now extinct may be found that will 

 explain the anomaly. 



Unfortunately, the prehensile lips and snout, so 

 well indicated bv the unique and very ancient bronze 

 head which Messrs. Spink, of St. James's, have 

 kindly permitted us to publish, would not be indi- 

 cated bv any of the bones. 



It may be that the animal was very scarce, and that 

 after its association with the detested deity it was 

 exterminated bv the Horus - following, orthodox 

 Egyptians. ' Joseph Offord. 



TECHNICAL OPTICS. 



THE establishment of a Department of Technical 

 Optics at the Imperial College of Science and 

 Technology, and the appointment of Mr. F. J. 

 Cheshire as the director of the department, were 

 announced in Nature of May 24 (p. 257). The report 

 of the Board of Education for the year 1915-16 just 

 issued (Cd. 8594, price 6d.) includes the following 

 reference to this subject : — 



.After many years of discussion the establishment of 

 a Department of Technical Optics is at last assured, 

 and the Board desires in this connection to express 

 its appreciation of the action of the London County 

 Council, to whom the realisation of the scheme is 

 largely due. The scheme involves the co-operation of 

 the Imperial College of Science and Technology at 

 South Kensington and the Northampton Polytechnic 

 Institute in Clerkenwell. The more elementary in- 

 struction will be given at the Northampton Polytechnic 

 Institute; the advanced full-time courses, and most 

 of the research work, will be centred at the Imperial 

 College. The work in technical optics at both insti- 

 tutions will be under the control of a director, who 

 will be a professor of the Imperial College, and will 

 be given the position of honorary head of a depart- 

 ment in the Northampton Institute. 



The governors of the Imperial College have ap- 

 pointed a Technical Optics Committee to manage 

 under them the work for which they are responsible; 

 and the London County Council has appointed the 

 same committee to advise it as to the work to 

 be done at the Northampton Institute. The Right 

 Hon. A. H. D. Acland, who is chairman of the Execu- 

 tive Committee of the Imperial College and a member 

 of the Committee of His Majesty's Privy Council on 

 Scientific and Industrial Research, has consented to 

 act as chairman of the Technical Optics Committee. 

 This committee will contain representatives of the 

 .\dmiralt}-, the War Office, and the Ministry of Muni- 

 tions, and also of employers and workers in the trade. 



At the outset the annual cost of maintaining the 

 new scheme is estimated to be not less than 5000Z., 

 while 5500I. is needed for alterations and equipment. 

 Of these sums the London Countv Council is pre- 

 pared to find 2000/. a year (including loooZ. for the 

 work at the Imperial College, and an increase of not 

 more than loooZ. in its maintenance grant to the 

 Northampton Institute), together with 750^. towards 

 the necessan,' equipment at South Kensington and 

 2500Z. for alterations and new equioment at Clerken- 

 well. The Board of Education will make an addi- 

 tional annual grant of 2000?. to the Imperial College 

 as from April i, 1917, and a capital grant of ,1500!. for 

 equipment, while the extended provision for technical 

 optics at the Northampton Institute will be taken into 

 account in fixing the amount of the Board's block 

 erant to that institution under the Regulations for 

 Technical Schools. The Department of Scientific and 

 Industrial Research is prepared to make a grant of 

 loooZ. a year for five years to the Imperial College 



NO. 2485, VOL. QqI 



and an equipment grant of 750/. in respect of the 

 research work which will be undertaken by the new^ 

 Institute of Technical Optics. 



Mr. Frederic J. Cheshire has been appointed head of 

 the new department at the Imperial College for a 

 period of five years, with the title Director of Technical 

 Optics and Professor of Technical Optics at the Im- 

 perial College. Mr. Cheshire's long experience and 

 great ability in optical matters practically .ensure a 

 successful beginning. He has been associated with 

 optical instruments for many years at the Patent 

 Office, and since the formation of the Ministry of 

 Munitions has been Deputy- Director-General of the 

 Ministrv and Technical Director of the Optical De- 

 partment of the Ministrv. He is the present president 

 of the Optical Society. ' It is expected that, subject to 

 the conclusion of certain arrangements with the 

 Treasure, Mr. Cheshire will accept the directorship, 

 and it is anticipated that the organisation of the de- 

 partment will be rapidly completed, and that training 

 will begin at an earlv date. 



THE CONFIGURATIONS OF 



ASTRONOMICAL MASSES AND THE 



FIGURE OF THE EARTHA 



A STUDY of the forms which can be assumed by 

 masses of actual compressible matter under their 

 own gravitation is of obvious importance for cosmo- 

 gony and astronomy. A theorem of fundamental im- 

 portance is that for a given mass, acted on by given 

 forces and rotating at a given speed, there is only one 

 equilibrium arrangement of the internal strata w^hen 

 the boundary is fixed. Thus possible figures of equili- 

 brium can be classified by their boundaries; the inte- 

 rior»matter will arrange itself. 



A simple application is to the figure of the earth. 

 Regarding the earth's surface as roughly spherical, 

 the internal layers of equal density must be concentric 

 spheres. The view that the internal strata may be, 

 or in some past age may have been, excentric, is 

 found to be illusory, and an attempted explanation of 

 the major inequalities of the earth's surface in terms 

 of this idea fails. 



A more complex application, is to ftie figures of com- 

 pressible masses, such as gases, in rotation. It is 

 found that a shrinking compressible mass will, in 

 general, assume in turn figures which rnay be described 

 as pseudo-spheroids and pseudo-ellipsoids, these being 

 derived by continuous distortion from the spheroids 

 and ellipsoids which form the only stable figures of 

 equilibrium for incompressible masses. The pseudo- 

 spheroids are more lens-shaped than a spheroid, and 

 the pseudo-ellipsoids are more spindle-shaped than 

 an ellipsoid. A sharp periphery may develop on the 

 pseudo-spheroid or a sharp point on the pseudo-ellip- 

 soid, in which case streams of matter are ejected 

 through centrifugal force outbalancing gravity. 



Considering in detail the figures appropriate to the 

 law P = Kpy, it is found that a sharp periphery will 

 develop on the pseudo-spheroids before the series of 

 pseudo-ellipsoids is reached, if y<.-^ (approximately). 

 Thus a mass of ideal gas for which 7<Jf can never 

 attain the pseudo-elliosoidal form and so can never 

 divide into two detached masses. But as the density 

 of an actual gas increases with shrinkage, the ideal 

 laws are departed from. The value y = '>, is reached, 

 perhaps, at a density of J to ^,_ rouerhly that of a 

 B-type star. So far, then, a "eiant" star can lose 

 matter equatorially, but cannot divide by fission. The 



1 Abstract of the RaWerian Lecture delivered before the Ro>-al Society on 

 May ir by Mr. J. H. Jeans, F.R.S. 



