NATURE 



[Dec. 25, i : 



obliquely upon a lens can be verified in an exactly similar 

 manner. It follows from the formula; given in Parkinson's 

 "Optics " (p. 101) that, with the usual notation — 



! . -- = sec-rj). 



H - V, Vj 



The verification of this formula by the method of observation 

 described above has been found to be a very useful and satisfac- 

 tory class experiment. W. N. Shaw 

 Cavendish Laboratory, Cambridge 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 



Cambridge. — The election of Mr. A. Marshall as Professor 

 of Political Economy will be welcomed by all who knew the 

 value of his work when formerly in residence as Lecturer at St. 

 John's College. 



The Senate has sanctioned the recommendation that 700/. be 

 expended on the purchase of microscopes for the biological 

 classes, on which sum interest at 4 per cent, is to be paid, a 

 small terminal charge being made to the students for the use of 

 the microscopes. 



The Botanic Garden Syndicate have recommended the increase 

 of the stipend of the Curator of the Botanic Garden from 150/. 

 to 200/. The Syndicate have watched with interest the zeal and 

 skill with which Mr. Lynch has applied himself to the conduct 

 and development of the garden. The improvement during his 

 curatorship has been very considerable, in fact remarkable ; and 

 the reputation of the garden among botanists and horticulturists, 

 both at home and abroad, has risen so much that it is now con- 

 sidered to hold a place in England second only to the Royal 

 Gardens at Kew. Sir Joseph Hooker has said that the Garden, 

 under Mr. Lynch's able management, is rapidly rising to emin- 

 ence as one of the very best in Europe. 'I he Syndicate express 

 their strong approval- of the assistance which Mr. Lynch's 

 intelligent appreciation of the requirements of botanical teaching 

 has enabled him to render to the University. 



Dr. Gilbert, Professor of Rural Economy at the University 

 of Oxford, and the associate of Sir J. B. Lawes in the Rotham- 

 sted experimental work, has accepted the post of H morary 

 Professor of Agricultural Chemistry at the Royal Agricultural 

 College, Cirencester, rendered vacant by the death of Dr. 

 Voelcker. 



Mr. D'Arcy Wentworth Thompson, B. A., was on Mon- 

 day elected Professor of Biology, University College, Dundee. 



SOCIETIES AND ACADEMIES 



London 

 Physical Society, December 13. — Prof. Guthrie, President, 

 in the chair. — The following communications were read: — On 

 the effect of an electrical current on the rate of thinning of a 

 liquid film, by Profs. A. W. Reinold, F.R.S., and A. W. 

 Riicker, F.R.S., read by Prof. Reinold. In 1877 the authors 

 communicated to the Royal Society an account of some experi- 

 ments upon the electrical resistance of liquid films. The results 

 then obtained showed that there was some disturbing influence 

 present, and the authors now find this to be the action of the 

 current upon the film itself. The films experimented on were, 

 as in the original experiments, cylindrical and vertical, formed 

 upon two coaxial platinum rings which are the electrodes by 

 which an electric current can enter or leave the film. The mode 

 of formation of these films and the precautions necessary to 

 keep them from gaining or losing moisture by condensation or 

 evaporation have been already described before the Royal 

 Society {.Phil. Trans., 1SS1, part 2). When such a film, just 

 formed, is left to itself, it shows a set of colours of different 

 orders arranged in horizontal bands ; as it thins under the action 

 of gravity, these bands gradually broaden out, and descend ; a 

 black band soon appears at the top, which likewise extends 

 downwards. If a current is now passed downwards through the 

 film, the motion of the colour-bands is accelerated, showing that 

 the effect of the current is to assist gravity in thinning the film ; 

 the black band, however, becomes in part or entirely white. 

 This upon examination is found to be due to the following 

 action ; the film is not directly dependent upon the upper ring, 

 but is attached to it by a comparatively thick mass of liquid. 

 The action of the current is to transfer liquid in its own direc- 



tion, thus, like gravity, thinning the film ; the mass of liquid, 

 however, on which the film hangs, by this same action is forced 

 down into the black portion, which consequently becomes 

 white. If the current be passed upwards, the reverse effects 

 occur : the downward motion of the bands is retarded, or, with 

 a strong current, reversed. The explanation is precisely the 

 same as before : the liquid is transferred along the film in the 

 direction of the positive current ; it sometimes collects in the 

 form of pendent drops attached to the upper ring ; these increase 

 in size, and stream down the sides of the film. Prof. Reinold 

 then formed a plane film between two horizontal wires ; the film 

 was illuminated by the lime-light, and its image projected upon 

 a scre*n ; the motion of the ban 's of colour in the direction of 

 the current produced by fifty Gr >ve's cells was clearly sh nvn. — 

 In a discussion which followed upon the transference of matter 

 with the current, Prof. Ayrton described some experiments 

 recently made by Prof. Perry and himself, which showed that 

 certain metals were carried through mercury in the direction of 

 the current. Mr. Boys remarked upon the apparent inertia of 

 the film ; the current seemed to require time to develop its 

 action, no motion of the colour-rings being visible for some 

 seconds after making the current. — Dr. Stone exhibited a 

 tuning-fork interruptor commutator. This is an instrument for 

 reversing an electric current through a circuit a given number of 

 times per second. From the free end of a spring, kept vibrating 

 in unison with an electrically maintained fork, by an electro- 

 magnet in the circuit of the fork acting upon an iron armature 

 attached to the spring, project two small aluminium plates, side 

 by side, but insulated by ebonite from the spring and from each 

 other. These are connected by fine wires, which do not inter- 

 fere with the vibration of the spring, to screws upon the lis, .1 

 the instrument, to which the poles of a battery are joined. The 

 motion of each plate is arrested upwards and downwards by 

 aluminium-stops, so that there are four such stops arranged at 

 the corners of a rectangle. They are connected in pairs 

 diagonally, and each pair is in communication with one end of 

 the external circuit. Thus, when the spring is up, the current 

 flows to the aluminium plates, and is transmitted through the 

 circuit in one direction; when the spring is down, it fl iws by 

 the lower slops in the opposite direction. The electromotive 

 force is thus reversed in the circuit twice as many times as (he 

 fork vibrates per second. — Mr. Lewis Wright exhibited his new 

 oxy hydrogen lantern microscope. Details of this instrument 

 will shortly be published. Geological, medical, and biological 

 specimens were exhibited upon the screen with great distinct- 

 ness, the definition being singularly perfect under the highest 

 powers. 



Anthropological Institute, December 9. — Prof. Flower, 

 F.R.S., President, in the chair. — The election of Miss Muller 

 was announced. — Sir John Lubbock read a paper on marriage 

 customs and relationships among the Australian aborigines. 

 Many tribes are divided into families or gentes, and no man 

 may many a woman of his own gens. For instance, among 

 the Mount Gambier (South Australia) natives every man is a 

 Knmite or a Kroki, every woman a Kumitegor or a Krokigor. 

 No Kumite may marry a Kumitegor, nor a Kroki a Krokigor. 

 In many cases the divisions are more complex, but the general 

 principle is that no man may marry a woman of the same gens as 

 himself. These divisions often extend through many tribes and 

 over hundreds of miles. But while these restrictions are im- 

 posed on marriage, on the other hand, in one sense, every man 

 is considered as a husband of every woman belonging to the gens 

 with which he is permitted to marry ; so that, as Messrs. Fison 

 and Llowitt forcibly put it, he may have 1000 miles of wive-. 

 But though we may call this marriage, and it is a right which in 

 old times was generally, and to a certain extent still is, recog- 

 nised as perfectly legal and respectable, it does not help us to 

 the origin of marriage in our sense. " Communal marriage " 

 (as he had proposed to cdl it) was no doubt aboriginal, and 

 founded on natural instincts. But how did the institution of 

 " individual marriage " arise? " Individual marriage ' cannot 

 be derived from "communal marriage," because, however much 

 the gentes may be subdivided, the wives must remain in com- 

 mon within the gens. Messrs. Fison and Llowitt did not, he 

 thought, sufficiently realise the fundamental distinction between 

 these two customs. They spoke of both as "marriage," and 

 indeed we had no other word for them. Vet they were radi- 

 cally distinct, and even opposite in their characteristics. Sir 

 John Lubbock had suggested, in his work on the "Origin of 

 Civilisation," that, while in such a state of things no man could 



