July 19, 1888] 



NA TURE 



287 



made to give constant potential when supplied at constant 

 potential except when the internal resistances are very small ; but 

 by over-compounding the distributing dynamo the desired result 

 may be obtained. Mr. Kapp agretd with the author as regards 

 motor-generators running with little sparking, but thought the 

 great difficulty in using them commercially would be in preserving 

 the insulation between the circuits, if anything like 2000 volts 

 were used in the primary. He also mentioned the method of 

 producing a rotating field by alternating currents, recently de- 

 scribed by Prof. Ferraris and Mr. Tesla, and thought it would 

 be preferable to the one devised by the author of the paper. In 

 reply, Dr. Thompson j-aid that insulation could be easily main- 

 tained between the core and windings of brush armatures, and 

 saw no reason why it should present very serious difficulties in 

 continuous current transformeis. — On an optical model, by 

 Prof. A. W. Riicker, F. R.S. The model exhibited and de- 

 scribed is to illustrate the character of the vibrations in a crystal 

 cut parallel to the axis, when plane-polarized light is incident 

 upon it. A rectangular glass box represents the crystal, and 

 glass plates placed at short distances from each end imitate 

 ^cd Nicols. A rod, carrying coloured circular and elliptical 

 rings and straight bars, passes along the axis of the box. These 

 rings are intended to indicate the character of the vibration at the 

 different points at which they are placed. The length of the 

 crystal is supposed to be such that plane-polarized red rays 

 emerge plane-polarized in the initial plane after being succes- 

 sively plane, elliptical, circular, elliptical plane, elliptical 

 circular, elliptical and plane-polarized within the crystal. All 

 the light is quenched by the analysing Nicol. Supposing light 

 of greater frequency (say green) to be used, another rod with 

 green ellipses, &c, is placed in the box, and illustrates that such 

 light emerges elliptically polarized, one component only of which 

 is stopped by the analyzer. This shows how plane-polarized 

 white light, when passed through crystals placed betwen Nicols, 

 may become coloured. — On a new barometer, by Mr. T. H. 

 Blakesley. A uniform glass tube is sealed at one end and a 

 thread of mercury introduced, inclosing a quantity of air. An 

 observation is taken by noting the volumes, A and B, of the in- 

 closed air (as indicated by the divisions on the scale) when the 

 tube is placed vertically with its closed and open ends upward 

 respectively. The height, H, of the b.irometer is given by the 



A + B 

 formula II = - /, where / is the length of the mercury 



A - B & J 



column in the tube. For convenience, / is made 10 inches. The 

 whole instrument is very portable, weighing only 6 ounces, and 

 measuring about 18 inches long.— In the absence of the author, 

 :a paper on the existence of an undulatory movement accompany- 

 ing the electric spark, by Dr. Ernest H. Cook, was taken as read. 

 When sparks pass between two points placed above a plate on 

 which some powdered substance has been scattered, the particles 

 arrange themselves in circular lines approximately concentric 

 with the projection of the middle line joining the two points. 

 The proximity of the lines is found to be very nearly constant for 

 the same powder, independent of the intensity of the spark used, 

 or the material of the plate. Different powders give different 

 numbers of lines per inch, and mixtures, numbers between those 

 corresponding to their constituents. A great number of sub- 

 stances have been tried, giving numbers between forty and eighty- 

 eii;ht per inch. These extreme numbers were obtained for chalk 

 and silica respectively. The author has fcund no satisfactory 

 hypothesis by which to explain the results. A number of photo- 

 graphs accompany the paper, showing the character of the 

 figures produced. At the meeting, an apparatus made by the 

 late Dr. Guthrie was exhibited, with which similar figures to 

 those described in the paper could be obtained. It consists of a 

 shallow elliptical dish covered by a glass plate. Sparks are 

 passed between two small knots across one focus, and powder, 

 sprinkled on the bottom, forms into circles about the other 

 focus. 



Anthropological Institute, June 26.— Francis Galton, 

 F.R.S., President, in the chair. — Mr. Arthur S. Burr ex- 

 hibited a collection of pottery and other objects from recent 

 excavations in New Mexico. — Mr. II. O. Forbes exhibited 

 a series of photographs taken by him in New Guinea. — A 

 paper on the Nicobar Islanders, by Mr. E. H. Man, was read. 

 Mr. Man has been resident at the Nicobars for periods amount- 

 ing in all to about 7 years, viz., 1871-88 ; during that time he 

 has prepared a vocabulary containing 6000-7000 words, and he 

 has thus been in a position readily to make inquiries from the 



natives on the various points of ethnological interest connected 

 with their constitution and their culture, and to substantiate from 

 a variety of independent sources all the information he obtained. 

 After giving a description of the islands and sketch of their 

 history, Mr. Man proceeds, working on the lines laid down in 

 the Anthropological Notes and Queries, to a careful considera- 

 tion of the constitution of the Nicobarese, which he prefaces 

 with an outline of certain facts and ethnic characteristics in 

 support of the racial affinities of the Nicobarese with the Indo- 

 Chinese races. From measurements taken of 150-200 indi- 

 viduals at the different islands, Mr. Man gives the average height 

 of the Nicobarese men as 5f, and of the women as 5 feet, a 

 result which disproves the statements of earlier writers regarding 

 the disproportion which exists between the sexes in respect of 

 size: The coloration of the skin pigment of the face, chest, 

 back, arms, and thighs is found to differ in a more or less 

 marked degree in each individual ; the two former are usually of 

 a distinctly lighter shade than the last three. Another error 

 needing correction is the assertion that these people can carry 

 without any trouble 200 cocoa nuts, or 5 cwts., whereas it 

 appears that in spite of their undoubtedly fine physical develop- 

 ment the maximum load which a Nicobarese can carry may be 

 reckoned as from 160-180 lbs. In the absence of statistics it is 

 difficult to speak with certainty, but from personal observations 

 extending over 17 years it would seem that the average length 

 of life among these islanders is higher rather than lower than it 

 is among the natives of the adjacent continents : the extreme 

 limit of life actually noted is a little over 70, and 80 may be 

 regarded as the maximum ever attained. With reference to the 

 numerical strength of the aboriginal population, a census taken by 

 Mr. Man a year or two ago proves that nearly half the popula- 

 tion of the group is contained in Car Nicobar, where a decided 

 increase is taking place, as is also the case at Chowra Teressa 

 and Bompoka. In the central and southern portions of the 

 Archipelago the small ratio of the juvenile element points, 

 however, to a diminution in those islands of the number of 

 inhabitants. It is satisfactory to learn that, though not entirely 

 exempt fiom the evils which seem inseparably connected with 

 advance in civilization, it does not appear that the Nicobarese 

 have suffered either physically or morally from their contact with 

 Europeans during the past 19 years. 



Entomological Society, July 4.-Dr. D. Sharp, President, in 

 the chair. — Mr. Enock exhibited male and female specimens 

 of a spider received from Colonel Le Grice, R A., who had 

 captured them at Folkestone on May 27 last. They had been 

 submitted to the Rev. O. Pickard-Cambridge, F. R.S., who 

 identified them as Pellenes tripunctatus, a species new to 

 Britain. Mr. Enock also exhibited specimens of Merisits 

 destructor (Riley), an American parasite of the Hessian fly. — 

 Mr. Wallis-Kew exhibited larva; of Adimonia tanaccti found in 

 Lincolnshire feeding on Scabious.— Mr. Porritt exhibited a 

 number of specimens of Arctia mendica, bred from a batch of 

 eggs found last year on a species of Rumcx at Huddersfield. 

 Mr. Porritt said that this species, in the neighbourhood of 

 Huddersfield, was often more spotted than the typical form, but 

 he had never before seen anything approaching in extent the 

 variation exhibited in these bred specimens. Out of forty-four 

 specimens not more than eight were like the ordinary type of 

 the species. — Mr. M'Lachlan exhibited specimens of Falirtgeuia 

 longicauda received from Rotterdam. — Mr. Jacoby exhibited 

 the following species of Phytophagous Coleoptera from Africa 

 and Madagascar, recently described by him in the Transactions 

 of the Society, viz. : — Lema latieollis, Cladocera nigripeuuis, 

 Oediovychis inadagaseariensis, Blepharida intermedia, B. nigro- 

 mactda'a, Chrysomela madagaseariensis, Sagraopaca, Blepharida 

 oruaticollis, B. laterimaculata, Mesodonta submetalliea, Schemati- 

 zclla vir.dis, Spiiocephahis viridipennis, Apophylia smaragidi- 

 peiniis, Acthonea variabilis. — M. Alfred Wailly exhibited a large 

 number of species of Lepidoptera and Coleoptera, recently 

 received by him from Assam, from the West Coast of Africa, 

 and from South Africa. He also exhibited eggs and living larvae 

 of Bombyx cytheraa, and made remarks on the life-history of 

 the species. 



Mineralogical Society, June 28. — Prof. Jas. Geikie, 

 F.R.S., in the chair. — The following papers were read: — A 

 mangano magnesian magnetite, by Prof. A. H. Chester, Hamil- 

 ton College, U.S.A. — The distribution and origin of the mineral 

 albatilein Ross-shire, by Hugh Miller, F.R.S., of H. M. Geol. 

 Survey. — Elaterite, a mineral tar in old red sandstone, Ross-shire, 



