Dfxember 31, 1 908 J 



NA TURE 



249 



1h: HcUquary a)>J llh-stratcd Archaeologist. Edited 



liy Rev. Dr. J. Charles Cox. New series, Vol. 



.\iv. Pp. 302. (London : Bemrose and Sons, 



I. id., 1908.) Price 12s. net. 

 'I'lir: quarterly numbers of this review are often 

 noticed separately in these columns on their appear- 

 ance. The Reliquary is devoted to the study of the 

 c.irly pagan and Christian antiquities of Great Britain, 

 mediaeval architecture and ecclesiology, the develop- 

 ment of the arts and industries of man in the past 

 ai^es. ;md the survivals of ancient usages and appli- 

 .inces in the present. The volume for the present year 

 c-imtaiiis an abundance of interesting text and excellent 

 illustrations, and should appeal to a wide circle of 

 readers interested in antiquities. 

 I he Class-room Atlas of Physical, Political, Biblical, 



and Classical Geography. Edited by E. F. Elton. 



Third edition, revised. Pp. vii + 48, plates + 11. 



(Edinburgh and London: \\'. and .\. K. Johnston, 



Ltd., 1908.) Price 5.S-. nei. 

 This widely known atlas has undergone a thorough 

 revision, and may be recommended to the careful 

 attention of teachers in .schools where geography is 

 regarded as a school subject of great educational 

 value. The editor has been successful in his aim of 

 providing clear maps, a full treatment of physical 

 features, and a series of climate charts u liich will 

 meet school requirements adequately. 

 Flaslies from the Orient, or a Thousand and One 



Mornings with Poesy. In Four Books : Spring, 



Summer, Autumn and Winter. Book second — 



Summer. By John Hazelhurst. (London : Hazell, 



Watson and Viney, Ltd., 1908.) Price is. 6d. 

 .Mr. Hazelhurst draws the inspiration for most of his 

 \xTse from natural objects and phenomena, but occa- 

 sionally current events, incidents relating to people 

 <il the day, and moral questions form the subjects of his 

 -.onnets. There are many evidences of the author's 

 \ersatility in the 295 pieces the book includes, and his 

 imagination and grace will please many readers. 

 I lie Country Home. Vol. i.. May to October, looS. 



Pp. ii + 380. (London : .Archibald Constable and 



Co., Ltd., 1908.) Price 55. net. 

 The first volume of this very attractive magazine, 

 iiintaining the monthly numbers one to six, is likely 

 In become a popular book in country houses. Nature- 

 -ludy takes a prominent place in the comprehensive 

 t.ible of contents, and much attention is given to 

 horticulture and other suitable pursuits for country 

 duellers. The illustrations are numerous and good. 



LETTER TO THE EDITOR. 



I Tlie Editor does not hold himself responsible for opinions 

 repressed by his correspondents. Neither can he undertake 

 lo return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 -Vo notice is taken of anonymous comnninicalions.] 

 The Objective Demonstration of the Rotation of the 

 Plane of Polarisation of Light by Optically Active 

 Liqu ds 

 Some years ago a method was described by N. Umow 

 I'/.eitschrift fiir physikalische Chemie, 1899, xxx., 711) for 

 I inonstr.nting objectively the rotation of the plane of 

 "ilarisation of light by an optically active liquid such as 

 I solution of sugar. The method was an ingenious 

 i|>plicatlon of Tyndall's experiment on the effect" of an 

 palescent liquid on a beam of polarised light. It con- 

 isted in rendering a concentrated solution of sugar some- 

 what turbid by adding to it a small quantity of an alcoholic 

 solution of resin ; on passing an intense beam of piano 

 polarised light into this solution spirals of light of the 

 spectrum colours were seen round the walls of the tube, 

 ilip colours being, of course, due to rotation dispersion. 

 Nome time ago, in order to show this phenomenon, I 



xn. 2n_;4, vot.. 7(1] 



made a slight modification of Umow's method in regard 

 to the solution, which appeared to be advantageous. A 

 concentrated solution of sugar was mi.xed with arsenious 

 oxide, and when as much of the latter had dissolved as 

 possible, the liquid was filtered, and sulphuretted hydrogen 

 gas passed through the filtrate. This gave a clear solu- 

 tion of sugar and colloidal arsenious sulphide, and when 

 an intense beam of plane polarised light was passed into 

 such a solution the phenomenon described by Umow was 

 very clearly seen, although some of the colours were 

 slightly interfered with by the yellow colour of the solu- 

 tion. 



For the purposes of a popular IccUire I recently pre- 

 pared a colloidal solution in water of arsenious sulphide 

 alone — to exhibit the Tyndall effect — and another as above 

 described, but I also filled a third tube with a solution 

 of sugar in water (made with tap-water and filtered 

 through ordinary filter paper). I proposed to point out 

 that a beam of plane polarised light passed through this 

 last tube should produce no effect, as the tube contained 

 a true solution. 



On trying the experiment beforehand, however, I was 

 surprised to find that the colours were nearly as distinct 

 as, and certainly purer than, in the case of the solution 

 which contained arsenic sulphide. It thus appears that in 

 order objectively to demonstrate optical rotation nothing 

 further than a clear aqueous solution of sugar is neces- 

 sary, and that Umow's addition of resin and mine of 

 arsenious sulphide were superfluous. 



It seems highly probable that the simple experiment 

 of passing a beam of plane polarised light sufficiently 

 intense to show the phenomenon can never have been 

 made before, otherwise the experimenter could not have 

 failed to be struck by the colours produced. 



As regards explanation, there seem to be two possi- 

 bilities : — (i) there may be in the solution containing 

 sugar and water a small quantity of foreign matter, either 

 in the colloid form or in such a fine state of subdivision 

 as to pass through the filter paper, these particles, as in 

 Tyndall's and in Umow's experiment, scattering light and 

 thus showing up the rotation ; or (2) the spirals may be 

 due to scattering of light by the sugar molecules them- 

 selves, which thus serve to show up their own rotation. 

 The decision nmst be left to those competent to discuss 

 the question. I will only mention in support of the first 

 suggestion that when a beam of ordinary light is passed 

 through the aqueous sugar solution slight scattering of 

 the light certainly occurs, as is shown by examination of 

 the light coming from the sides of the tube, by means of 

 a Nicol prism. On the other hand, however, the colours 

 seen in the tube containing sugar and water alone are but 

 little inferior in intensity to those seen in the tube contain- 

 ing arsenious sulphide. 



I have also passed a beam of plane polarised light 

 through a tube containing a very pure specimen of menthyl 

 acetate (fa]o""°= — yq^-s) which had been carefully dis- 

 tilled. The colours were quite apparent in this case also, 

 being purer, but not so intense as with the sugar solution. 

 The scattering of ordinary light by the menthyl acetate 

 was very slight indeed. 



Whatever the cause of the phenomenon may be, it is a 

 very simple matter to demonstrate objectively to a large 

 audience the rotation of the plane of polarisation of light. 



T. S. Patterson. 



Organic Chemistry Laboratory, I'niversity of 

 Glasgow, December 18. 



THE FINANCIAL STATUS OF THE 



UNIVERSITY PROFESSOR.^ 



'X'HE Carnegie Foundation for the Advancement of 



■'• Teaching was instituted for the betterment of 



the calling of the teacher in the United States, the 



Dominion of Canada, and Newfoundland. Its first 



1 "The Financi.->1 Status of the Prote'S'inr in America and in Germany.' 

 Bulletin No. 2 (New York : The Carnegie Foundation for the Advance- 

 ment of Tearhind, »qoR ) 



" The Relat ons oi Christ!.->n Denominations to Colleses " An Address 

 before the Conference on F.di canon of the Methodi«t Episcopal Church. 

 South, at Ailanla, Ga., May 20, 1508. By Henr- Prit hett. President of 

 the Carnegie Foundation. (Printed at Nashville, Tennessee, iqoB.) 



