576 



NATURE 



[October 3, 1907 



things, the law that the optical effect varies as the 

 square of the resultant electric force. 



At the meeting of the British Association in Glas- 

 gow in 1876, the president, Prof. Andrews, made a 

 pointed reference to these early e.xperiments of Dr. 

 Kerr, but little dreamed that in a few days the whole 

 scientific world would be positively " electrified " bj' 

 the announcement of the great discovery known as 

 the Kerr effect. Not only did Kerr announce the 

 discovery, but he demonstrated it with the simplest 

 of apparatus before the meeting of Section A. The 

 paper containing a full account of these experiments 

 was published in 1877 {Phil. Mag., vol. iii., pp. 321- 

 343). The great fact established was that the plane 

 of polarisation of a ray of plane polarised light re- 

 flected from the end of the iron core of an electro- 

 magnet is rotated under influence of the magnetising 

 current, in a direction contrar)' to the conven- 

 tional direction of the current. In a later 

 paper (Pliil Mag., vol. v., pp. 161-177) the like 

 phenomenon was established for light reflected from 

 the sides of the magnetised iron. These remarkable 

 experiments form the starting point for a prolonged 

 series of delicate measurenients in magneto-optics by 

 several experimenters, of whom we may mention 

 specially Righi, Kundt, Du Bois, Sissingh, Zeeman, 

 and Drude. 



On the theoretical side Fitzgerald (Phil. Trans., 

 1880) was the first to attempt a discussion of the Kerr 

 effect. In this effort he broke "new ground," as 

 Maxwell expressed it ; and although the theory was 

 not comprehensive enough, nevertheless (to quote from 

 Larmor, who has himself greatly developed the whole 

 electromagnetic theory) " Fitzgerald's analytical work 

 still remains applicable. The extension to metallic 

 media is now formally made, as Ohm's law indicates, 

 by taking the refractive index to be a complex quan- 

 titv ; with this generalisation the analysis has been 

 extended by various writers, including Lorentz, Gold- 

 hammer, and Drude, but most completely by Leathem 

 and Wind, and shown to embrace satisfactorily all the 

 mass of detail that has been brought out in recent 

 years in experimental magneto-optic investigations." 



Dr. Kerr's latest paper on this subject (Proceedings 

 of the Royal Society, 1894) described experiments on 

 a fundamental question in electro-optics : " Reduc- 

 tion of Relative Retardations to Absolute." In 1888 

 (Phil. Mag., xxvi., pp. 321-341) he published a well- 

 planned and carefully-executed series of experiments 

 on the birefringenl action of strained glass. His last 

 contribution to scientific literature was a note read 

 before the British Association in 190 1 on the " Brush 

 Grating and its Optical Action." 



Before the great scientific events of his life the 

 University of Glasgow showed their appreciation of 

 Dr. Kerr as an educationist by conferring on him 

 in 1868 the honorary degree of Doctor of Laws. He 

 was elected F.R.S. in 1890, and was awarded a Royal 

 medal in 1898. He died .\ugust 18, 1907, after 

 enjoying six years' retirement from ofiiclal duties in 

 the Normal College. Here, in limited accommodation, 

 with still more limited apparatus, and onlv by devot- 

 ing evening hours and precious holidays to research, 

 John Kerr made the discoveries which have linked his 

 name for all time with that of the immortal Faradav. 



C. G. K.' 

 NO. 1979, VOL. 76] 



NOTES. 

 Prof. .M. H. E. Tscuekni.ng, director of the ophthalmo- 

 logical laboratory of the Sorbonne, Paris, has accepted 

 the invitation of the council of the Optical Society to 

 deliver the first Thomas Young oration on Thursday, 

 October 17, and has chosen for its title " The Develop- 

 ment of the Science of Physiological Optics during the 

 Nineteenth Century." The oration has been established 

 for the purpose of providing an annual lecture on some 

 subject connected with physical, geometrical, or physio- 

 logical optics, and thus to further the development of 

 those branches of science with which the name of Thomas 

 Young is intimately associated. The orator is elected 

 annually by the council of the Optical .Society from persons 

 eminent in these branches of science or technology. 



.\ \ERY interesting and instructive exhibit has just been 

 added to the public galleries of the geological depart- 

 ment of the British Museum (Natural History) in the form 

 of an enlarged wax model of the Silurian arachnid £i(ry- 

 ptenis fischeri. Remains of these creatures are found in 

 such a wonderful state of preservation in the Upper 

 Silurian strata of Oesel, in the Baltic, that Prof. G. 

 Holm has .succeeded in freeing from the matrix consider- 

 able portions and mounting them on glass slides in Canada 

 balsam. The original chitin is preserved in an almost 

 unaltered condition, and even the most minute details of 

 the external surface are retained. From these materials 

 it has been possible, under the superintendence of Dr. 

 Caiman, to construct the model now exhibited, which is 

 double the natural size, and appears to be between 7 inches 

 and 8 inches in length. The model -is temporarily placed 

 in the central hall. 



We learn from the British Medical Journal that a move- 

 ment for the foundation of an institution which is to 

 bear the name of Prof. Robert Koch is on foot in 

 Germany, and a committee has been formed with the 

 object of collecting money for the purpose. The chairman 

 is Dr. von Studt, Prussian State Minister ; the vice-presi- 

 dent, Privy Councillor AlthofT ; the- secretary, Prof. 

 Schwalbe, editor of the Deutsche medizinische Wocheti- 

 schrift • the treasurer, Dr. Paul von Schwabach, General 

 Consul, Berlin. The institution, which is to be applied 

 to the furtherance of research in all directions for the dis- 

 covery of means of checking the diffusion of tuberculosis, 

 is intended to be a permanent memorial of the discovery 

 of the tubercle bacillus by Prof. Koch twenty-five years 

 ago. Appeal is made for contributions sufficient to make 

 the institution a tribute of gratitude to Koch, similar to 

 those with which the name of Pasteur has been honoured 

 in France and that of Lister in England. 



It is announced in the Times that the Government has 

 completed negotiations for the purchase of the estate of 

 Inverliver, Argyllshire, with a view to its conversion into 

 a State forest. The estate, which has an area of about 

 12,530 acres, extends for about nine miles along the 

 western side of Loch Awe, stretching across to Loch 

 Avich. It will be of much value as a centre of education 

 in forestry, and arboriculturists in Scotland arc gratified 

 that their desires for the establishment of a demonstration 

 area are about to be realised. The afforestation of Inver- 

 liver will at once be proceeded with according to a general 

 scheme, which provides for a certain number of acres 

 being planted each year. The estate will be under the 

 management of the Office of Woods and Forests, and, 

 though it will yield no immediate return, it is expected 



