Iam-ary 2. 1919 



NATURE 



359 



1 1,. would admil to the'si 1 oursi - onlj those 



by having v ssfullj in a laboratory, 



, u l,l be in 11 position to app I thi insti uction. 



- 1 on insists thai the value of this teai 



1 depend upon the soundness of its 

 ['he teaching should no 

 1 ople, philosophers, <>r anyone 

 ial v. aj . bul must 

 chiel purposi I" ing to 

 interpret thi pirit and methods. The- ulti- 



mate aim of the 1 1 humanise science, and 



- give it its due part in a general scheme of 

 tion. 



SOCIETIES AND ACADEMIES. 

 London. 

 Optical Society, Decembei Prof. F. J. Cheshire, 



n the chair. Instructor-Corn. T. Y. Baker 

 I L. N. G. Fllon : An empirical formula for 



dinal f a 1 a\ through a thick 



lens. I lii authoi hat thi development of 



mgitudinal aberration as .1 po is fre- 



h illegitimate owing to lis divergence foe com- 

 parative!) slight inclinations of the rays, instead oi 



s,uch development of thi . . ., where 



/ is tin- tangent ol the inclination of the ray, the} pro- 



.1 formula I nined \ and 



B numerically from the values of the aberration of 



ilculated trigonometrically through .1 



lens. This was dene for a wholi image 



his and for a whole series ol lenses ol different 

 shapes but of the same focal length. The numerical 

 \ alues oi \ and B then analysed, and 



an end( a\ oui wa - late gi nei .1] 



fornuilae foi them in terms of the image position and 

 i In authoi s d( cided that in all eases 

 the value A in theii empirical formula and the value a in 

 the power series wen- practically identical, The value 

 .is given b; thi authors in a paper read befon 

 the societ} in May. The value of B can be expressed 



ubii in \l, the lineai magnification of the imagi . 

 I hu- B B B M B M • B M . in which the four 

 1 [efficients B„ B,,B : , and B are all quadratic functions 

 oi the mean curvatun of thi lens faces.— Major E. (). 

 Henrici • Spirit-levels. The best bubble tubes for spirit- 

 levels have heen made in ( ,< rmair. ; it seems desirable 



an investigation should be made of the factors 



- ■ u\ for producing satisfactory tubes. The advan- 



- a lone air-bubble, as regards both the accuracy 

 ipidity with which the bubble comes to rest when 



lointed out, and also the advantage of 

 aius of curvature as regards the latter point. 

 The radius of cm .els, the sensitive- 



must, howi v< r, be sufficiently great for the bubble 

 noticeably with the smallest angular tilt ol 

 ube which ii is desired to indicate. If the bubble 

 sitivc, time is losl ; if it be not sufficiently 

 sensitive, a spurious idea of accuracj is given; thi 

 ness ol ever; bubble tube for accurate work 

 should be marked. The mi thods of mounting, illu- 

 minating, and viewing the bubble tube frequently 

 much to be desired, and improvements in these 

 matters lead to increased accuracy for a given sensi- 

 tiveness. Several methods of viewing by means of 

 prisms were described, the most satisfactory known 

 the author being one placed on the market by Zeiss. 

 The accuracy of shaping the surface required in a 

 sensitive bubble is very gnat. If a tube has a cor- 

 the corrugations having an amplitude 

 mm. and a period of 10 mm., the angle of 

 tilt to move the bubble 1 mm. may vary 38 per cent, 

 its nominal value in the ease of a bubble with a 

 litiveness of 10 seconds per mm., the bubble being 



Z566, VOL. I02] 



55 mm. lone. A similar corrugation with a 2-second 

 bubble will make it almosl useless for any purpose. 

 Further investigation is required into the effect of the 

 following faetms on the performance of the bubble: 

 Quality, polish, and cleanliness of the glass; quality 

 .,",,,1 purit; oi thi liquid and vapoui in the tube, and 

 mi thods ol mounting and viewing. 

 Uistotelian Society, Di -Prof. Wildoti 



(air, vice-president; in the chair.— Prof. J. Laird: 

 Synthesis and discovery in knowledge. The paper 

 consisted of a discussion of two sharply contrasted 

 views of knowledge (viz. thai knowledge is essentially 

 the inspection or thi discovery of an object which is 

 given or revealed, and that knowledge is essentially 

 a process of organisation or construction on the part 

 oi the mind), together with a consideration of certain 

 hypotheses designed to mediate between these extremi 

 The general argument was that while the 

 In,, of these'alternatives could be defended agains' 

 many of the objections commonly brought against it, n 

 was ultimately inadequate, since representative con- 

 struction in words, images, 10., is plainly an integral 

 ,,.,,1 ,,t mosl varieties ol knowing. An examination 

 oi the theory that knowlei ays the inspection 



of a construction showed (1) thai in this case the 

 product of construction required to be apprehended 

 directly and (2) that such a product could be known 

 i. representative only if the things represented 

 r, directly apprehended, in some instances at least. 

 The theory" that knowledge consists of construction 

 til was claimed) was therefore refuted, and the rest 

 of the argument consisted of a detailed investigation 

 into the 'truth of the statements that the object of 

 knowledge is always (in some sense) a mental pro- 

 duct on the ground that this object is always a 

 unity" o, "a meaning," or that mental imageryis 

 always an essential part of it. The author_ main- 

 tained that these arguments were either fallacious or 

 inconclusive. 



Paris. 

 Academy of Sciences, December 9, [918.- M. P. 

 Painleve in the chair.— E. Picard and A. Lacroix : The 

 second meeting of the Inter-Allied Conference of 

 Scientific Academies. An account of the resolutions 

 passed at the meeting held at Paris. November 26 

 to •,, (see Nature, December 2(1, 1918, p. 325) 

 I Orach: Integration of a partial differential equation 

 of the dynamics of fluids, -A. Buhl: The extension to 

 multiple' integrals of the theorem concerning the ex- 

 change of the amplitude and parameter in hyper- 

 elliptic integrals.— A. Lambert: Certain polynomials 

 connected with Laplace coefficients. Ch. Fremont: A 

 new machine for measuring the resistance of cast- 

 iron b\ the method of chiselling.- Ch. Oorceix : The 

 probable correlation of the displacements of level of 

 tl„. base .and the oscillations ol glacial fronts. v. 

 (iuebhard • \ possible conciliation between the two 

 theories of volcanic action.— M. Molliard : The sapro- 

 phytic life of an Entomophthora. 'I his fungus (£. 

 henrici), developed originally on a Culex pipiens, has 

 been grown successfully on the sterilised grub of 

 Euchelia jacobaeae, on sterilised ox-liver, and even on 

 carrot, but in the last-named the cultures are not so 

 abundanl a- on liver. Hence this species is not 



„ aril) parasitic— F-X. Skupienski : Sexuality in 



Dictyosteliam mucoroidcs.—L. Roule : The state of 

 spawning salmon during their migration into fresh 

 water in France. From the examination of eighty 

 Ssh taken a' different periods it is concluded that for 

 -i two years voung salmon live in fresh water, 

 and then descend to the sea, growing there for a- 

 ,1 riod varying from two to four years. Then, at 

 the age of between four and six vears, they return to 



