46 



NATURE 



[May 14, 1891 



sidereal time. A modified and improved instrument, devised 

 by my assistant, Mr. Edward E. Robinson, adds a sighted 

 pointer to the dial, this pointer being moved by hand to the 

 right date ; and the clock may then keep ordinary time. The 

 dial is geared down i : 24, and driven by the minute hand, so as 

 to be under the ordinary control of clock-regulation. In each 

 instrument a one-day hand-shift is needed every 29th February. 

 — (3) Resonant Leyden jars. A couple of independent but similar 

 Leyden jar circuits arranged at a moderate distance from each 

 other, the self-induction or capacity of one of them being ad- 

 justable, with an easy overflow path. On discharging one of 

 the jars, the other resounds and overflows, being provided with 

 an easy overflow path. The oscillations are much more numerous 

 than with ordinary linear (Hertz) vibrators, and therefore some 

 precision is demanded in the tuning. 



Self-recording instruments, exhibited by MM. Richard Freres. 



Method of recording pyrometric measurements at temperatures 

 between 600° C. and 1200° C, exhibited by Prof. Koberts- 

 Austen, C.B., F.R.S. The apparatus is that employed in a 

 research undertaken for the Institution of Mechanical Engineers, 

 and is used for automatically recording, by the aid of photography, 

 the indications of a platinum and platinum-rhodium thermo- 

 couple. The experiments shown illustrate a method of recording 

 the rate of cooling of heated masses of metal. Curves are 

 shown to illustrate the kind of results which are obtained by the 

 aid of the apparatus. 



Length-measuring instrument, exhibited by Prof. W. C. 

 Unwin, F.R.S. In ordinary screw or vernier micrometers the 

 straining of the instrument alters the readings, and in using the 

 instrument much depends on personal skill. In this instrument 

 the contact is with fixed pressure, and independent of feeling. 

 Delicate levels show when the instrument is adjusted. 



Portraits of deceased astronomers and physicists, exhibited by 

 Mr. W. B. Croft. 



Mr. Killingworth Hedges exhibited: — (i) Electrical safety- 

 valve. — (2) Exhausted bulbs, used to ascertain the space traversed 

 by high tension alternating currents. The electrical safety-valve 

 is designed for attachment to low pressure service lines, in order 

 to prevent their being charged at a dangerous difference of 

 potential from the earth. The glass bulbs were exhausted to 

 different pressures, and fitted with electrodes of various forms, 

 in order to ascertain if an arc could be started with an E.M. F. 

 of 300 volts, which is the limit of potential fixed by the Board 

 of Trade for currents of low pressure. 



Focometer, exhibited by Prof. Silvanus P. Thompson, By 

 this instrument can be determined the position of the two 

 principal "focal planes " and of the two " principal planes" of 

 Gauss, for any compound system of lenses, such as a microscopic 

 objective or the lens of a photographic camera ; thus giving the 

 true focal length, and the positions and distance apart of the 

 two virtual optical centres of the lens-system. The principle 

 applied is that of finding directly the two principal foci, and 

 then, by means of a right-and-left-handed screw, moving two 

 .micrometers placed at these foci to the two symmetric points 

 where each micrometer coincides with the image of the other. 

 The displacement so given by the screw is equal to the true focal 

 length. 



Mr. Shelford Bid well, F.R.S., exhibited: (i) Selenium 

 cells, the electrical conductivity of which is greater in the light 

 than in the dark. (2) A selenium lamp-lighter, lighting an in- 

 candescent lamp automatically when darkness comes on. (3) A 

 selenium alarm, for calling attention to the accidental extinction 

 of a ship's light or railway signal lamp. — Mr. W. Crookes, 

 F.R.S., exhibited electricity and high vacua. — Mr. G. J. Symons, 

 F.R.S., exhibited photographs of damage produced by the 

 tornado of August 18, 1890, at Dreux (Eure et Loire), France. 

 — Prof. C. Piazzi Smyth exhibited examples of photographic 

 enlargements of the solar spectrum, each magnified from the 

 original negative from 25 1027 times linear. — Mr. George Higgs 

 .exhibited photographs of the normal solar spectrum. 



M. G. Lippmann exhibited colour photographs of the 

 ■spectrum : — (i) Small spectrum, exposure about 3 minutes. — 

 >(2) Large spectrum, exposure about 6 minutes, without coloured 

 screens. The colours seen on these plates are produced by the 

 direct action of light ; they are not due to any pigments, the 

 substance of the films remaining colourless, but are of the same 

 kind as the colours of soap-bubbles and mother-of-pearl, viz. 

 interference phenomena ; they are due to the structure imparted 

 to the film by the stationary waves of incident light during 

 exposure in the camera. These colours are perfectly permanent, 



NO. I I 24, VOL. 44] 



Prof. A. Schuster, F.R.S., exhibited some forms of Clark 

 cells. 



Prof. Emerson Reynolds, F.R.S., exhibited : (i) Specimens 

 of tetrathiocarbamid-ammonium bromide, (H5N2CS)4NBr, and 

 related substances. (2) Series of photographs I'llustrating the 

 application by Colonel Waterhouse of the above bromide to the 

 reversal of the photographic image on gelatino- bromide of silver 

 films. — Mr. W. Saville-Kent exhibited photographs of living 

 corals, taken in Torres Straits. — Dr. W. Hunter exhibited a 

 series of ptomaines — alkaloidal products formed by bacteria 

 from animal tissues. — The Committee of the Camera Club 

 exhibited allotropic forms of silver, prepared by Mr. Carey Lea, 

 of Philadelphia, and described in Ainer. Journ. of Science for 

 1889, and Phil. Mag for 1891.— Prof. G. F. Fitzgerald, F.R.S., 

 exhibited crystals of platinum and palladium (prepared Mr. T 

 Joly).— Prof J. A. Ewing, F.R.S., exhibited Prof. Sekiya's 

 model of a Japanese earthquake. — The Council of the Royal 

 Society exhibited a cabinet containing medals struck in honour 

 of Fellows of the Royal Society. — Mr. Edward Schunck, 

 F.R.S., exhibited indigo-blue and allied substances and deriva- 

 tives of chlorophyll.— Mr. Fred Enock exhibited microscopic 

 preparations of the British Mymaridae (egg parasites). — Dr. H. 

 Woodward, F.R.S., exhibited skull and shoulder-girdle of 

 Procolophon trigoniceps (Owen), collected by Dr. Exon in the 

 Orange Free State (figured Phil. Trans., 1889, p. 267).— Mr. J. 

 Howard Mummery exhibited specimens illustrating some points 

 in the structure and development of dentine. — Mr. Allan Dick 

 exhibited a new form of polarizing microscope. 



Meteorological photographs, exhibited by Mr. Arthur W. 

 Clayden. The photographs of clouds have been taken by 

 reflection from a mirror of black glass, placed in front of the 

 camera, so that the plane of its surface makes the polarizing 

 angle with the axis of the lens. Those of hoar-frost show how 

 the crystals attach themselves to the projecting portions of 

 objects, such as the margins of leaves, the loose fibres of a 

 string, and the thorns of a briar, and also their tendency to 

 grow towards the direction from which the air has been moving. 



THE BENUi AND THE KIBB^. 



A T Monday's meeting of the Royal Geographical Society, 

 ■^*' Major Claude M. Macdonald, H.M. Commissioner to 

 West Africa, gave an account of a journey up the Benue and 

 its northern tributary the Kibbe, in the summer of 1889. The 

 Benue, we need scarcely say, is the great tributary of the 

 Niger. Major Macdonald referred to the previous explorations 

 of Barth and others, and to the fact that it has been maintained 

 that a connection existed between Lake Chad and the Benue, by 

 the overflow of the Shari on one side and the Kibbe on the 

 other. Major Macdonald has been the first to explore the Kibbe. 

 After describing the ascent of the Benue, Major Macdonald 

 went on to say that he and his party started on their journey up 

 the Kibbe in the Royal Niger Company's stern-wheeler the 

 Benue, on August 21. 



The Kibbe at its mouth is some 250 yards wide, while the 

 Benue is upwards of 600. The average depth of the Kibbe 

 at this season of the year, nearly high water, is from 10 to 12 feet. 

 On both banks for the fir.-^t five miles the country is flat and 

 well wooded, with patches of bright green grass, and looks very 

 gamey, though owing to the high grass we saw no deer. A 

 noticeable feature some five or six miles from the river is Mount 

 Katie, a rounded hill, some 800 feet high, well wooded to its 

 summit. This hill, from its isolated position, served as an 

 excellent point on which to take angles for mapping purposes. 

 Patches of cultivation were now to be seen on both banks, and 

 after two hours' steaming the party passed the Fulbe village of 

 Dinghi. The inhabitants, though they had never before seen a 

 steamer or a white man, did not seem much disconcerted, and, 

 when shouted to in their language, returned the salutations in a 

 very friendly manner. On August 22 the Borne anchored off a 

 large village on the left bank. " We very soon saw," Major 

 Macdonald states, "that we had to deal with the purest-bred 

 Fulbe we had seen so far. The crowd consisted almost entirely 

 of women — by far the best-looking we had as yet seen on the 

 Niger, and indeed the best-looking I have seen in either east or 

 west Equatorial Africa. They wore the usual piece of cloth 

 wound round their bodies, leaving their arms and shoulders 

 bare, and reaching down below the knee. Their features, in 

 most cases, approached the European, and their expression most 



