August 2, 19 17] NATURE 



459 



at about sixteen years of age must have completed an 

 approved course m science. These are a few only of 

 the demands of the assistant-masters, but they will 

 serve to show how far behind the ideals of this body 

 of schoolmasters is the present system of education 

 in this country. 



Two courses of twelve lectures each on "The De- 

 signing and Computing of Telescope Systems " will be 

 delivered at the Imperial College of Science, South 

 Kensington, bv Prof. A. E. Conrady, during this 

 month and next, commencing on August 13. The lec- 

 tures will be given in connection with the newly 

 formed department of technical optics at the college, 

 under the direction of Prof. F. J. Cheshire. The im- 

 portance of optical designing and computing, together 

 with evidence of its neglect in the past by English 

 opticians, has been one great lesson of the war. Seri- 

 ous delavs in the production of optical munitions have 

 arisen from the inability of manufacturers to obtain 

 the necessary constructional data for the systems re- 

 quired. Many manufacturers are still under the. im- 

 pression that satisfactory designs cannot be obtained 

 without the making up of a succession of saniples in 

 the workshop, in each one of which an attempt is made 

 to correct the errors found by the testing of the sample 

 which immediately preceded'it. Experience has shown, 

 however, that the necessar\- constructional data, such 

 as curves, diameters, thicknesses, and separations for 

 given glasses, can be obtained by calculation alone, and 

 that so satisfactorily that a manufacturer is justified 

 in putting in hand an order for a large number of 

 systems without the making up and testing of a single 

 sample. In first-class designing the trial-and-ei;ror 

 work is done on paper only, whereas by the older and 

 less efficient methods the theoretical trial-and-error 

 work of the computer must be checked and tested 

 from time to time by practical trial-and-error work on 

 a number of workshop constructions. The rnanufac- 

 turer of the future who is not in a position to enlist 

 as required the serxices of a competent designer — that 

 is, one capable of producing satisfacton.' designs by 

 pen-and-paper work only — will, therefore, be at a great 

 disadvantage as compared with competitors who have 

 such assistance available. The courses of lectures at 

 the Imperial College have been decided upon for the 

 immediate purpose of assisting manufacturers in the 

 production of optical munitions of war, but at the same 

 time thev will give to those manufacturers an oppor- 

 tunity- of furthering the technical education of such of 

 their employees as are, or will be, responsible for the 

 scientific direction of their work in matters of optical 

 design, and thus ensure, so far as possible, favour- 

 able conditions for entering into that keen commercial 

 struggle which must inevitably follow the attainment 

 of peace. The lectures will appeal also to those who, 

 having the necessary mathematical knowledge, are 

 anxious to learn the theors' and practice of optical 

 designing. Intending students should applv to the 

 Director, Technical Optics Department, Imperial Col- 

 lege, South Kensincfton, London, S.W.7. 



SOCIETIES AND ACADEMIES. 



London. 

 Geological Society, June 20.^ — Dr. Alfred Harker, 

 president, in the chair. — Dr. A. Holmes : The Pre- 

 Cambrian and associated rocks of the district of 

 Mozambique. Beyond the coastal and volcanic beds 

 of Mozambique (described in a previous contribution, 

 Abs. Proc. Geol. Soc., 19 16, No. 994, p. 72) the 

 country assumes the form of a gently undulating 

 plateau, gradually rising towards the west and diversi- 

 fied by innumerable inselher^ peaks and abruptly 



XO. 2492, VOL. 99] 



rising clusters of hills. The dominant rock through- 

 out is a grey biotite-gneiss. Interfoliated with this 

 are occasional lenticular masses of hornblende-gneiss 

 and amphibolite, and within these smaller bands of 

 crystalline limestone are sometimes preserved. Schists 

 — referable to arenaceous sediments — are found only 

 near the coast, where they are interbanded with 

 gneisses; and, as the latter are mainly of igneous 

 origin, they are thought to be intrusive into, and 

 therefore younger than, the schists. The succession of 

 rocks in eight of the better-known districts is described, 

 and a general classification based on the details is 

 given. The correlations of certain groups of rocks 

 with the Lower and Middle Pre-Cambrian of other 

 regions are based on the determination of lead- 

 uranium ratios of zircons derived from the gneisses 

 and granulitic granites respectively, the zircons having 

 been obtained by crushing and panning the rocks in 

 the field. The gneisses give a ratio of 0-21, comparable 

 with a ratio of 024 obtained for Canadian zircons of 

 Laurentian age. The granulitic granites give ratios 

 of 0-14 to 0-17, comparable with those of radio-active 

 minerals of late Archaean — that is, late Middle Pre- 

 Cambrian— age in Scandinavia (Moss 012 to 015, 

 Arendal 016 to 018, and Ytterby 015 to 017), Canada 

 (Villeneuve, Queibec, 017), and India (Singar 014). 

 The rocks are described in detail, with tables giving 

 the quantitative mineral composition ond the specific 

 gravities and radium contents. — L. Richardson : The 

 inferior oolite and contiguous deposits of the Crevx- 

 kerne district (Somerset). A detailed description is 

 given of the inferior oolite of the Crewkerne district. 



Edinburgh. 

 Royal Society, Julv 9. — Dr. J. Home, president, in 

 the chair. — Prof. A. Robinson : The origin, rupture, and 

 closure of ovarian follicles. In the ferrets and pole- 

 cats there are two distinct growth periods : (i) a period 

 of relatively slow growth extending over several weeks ; 

 (2) a period of rapid growth lasting from twenty to 

 fortv-eight hours. During the first period the cavity 

 of the follicle forms, and is filled as it forms, with a 

 viscid tenacious "primary" fluid, which gradually be- 

 comes membranous at it's peripher}-, where it is inti- 

 mately connected with the follicular epithelium. Dur- 

 ing the second period a much less viscid " secondary " 

 fluid is quickly formed amidst the epithelium of the 

 ovarian cumulus, which is simultaneously disintegrated 

 and dispersed. Thereafter the secondan,- fluid forces 

 its way, between the membranous periphery of the 

 primarv fluid and the follicular epithelium, to the apex 

 of the follicle. Under increasing pressure the follicle 

 ruptures, and the ovum, v,ith its corona of follicular 

 epithelium, the disintegrated cumulus epithelium, the 

 whole of the secondary fluid, and part of the primary 

 fluid are evacuated and pass into the oviduct. The 

 rerhainder of the orimary fluid fills the remnant of the 

 cavity of the follicle and plugs the orifice through 

 which the contents escaped. So soon as the orifice is 

 plugged distension of the follicle recommences, and 

 fluid again accumulates in its interior. Simultaneously 

 the orifice contracts, the plug shrinks, and in frorn 

 thirty to forty-eight hours the orifice is completely 

 closed, and the follicle again fully distended. The 

 formation of the secondary fluid depends upon in- 

 semination. The follicular epithelium becomes vascu- 

 larised before the rupture takes place, but there is no 

 effusion of blood when this occurs.— Prof . D. Waterston : 

 Development of the heart in man. Reconstructions of the 

 hearts of embryos at different stages of development 

 were exhibited and their indications discussed. They 

 showed clearlv the profound changes which take place 

 in the structure of the heart, changes which occur as 

 the heart is carrying- on its functions. Another point 

 dealt with- was the mechanism of the subdivision of the 



