476 



NA TURE 



[March 19, 1885 



account of its weight, become extended at its base and conse- 

 quently change its form — a circumstance which would prove very 

 prejudicial to the experiments contemplated in connection with 

 it. Dr. Konig and Dr. Richarz had, therefore, calculated the 

 pressure exercised by the lead mass, which should have a basal 

 plane of I 9 square metres, on the square centimetre, and had 

 found it equal to 23 kg. They then prepared a small lead 

 cylinder, placed it with due underlayers on the earth, and by 

 means of pulleys and weights caused a constant pressure of more 

 than 6 kg. per square centimetre to be exerted on its smooth 

 upper surface. Two fine steel spikes were fastened in the side 

 of the lead mass, and their distance from each other exactly 

 measured. After this pressure had been exerted for a consider- 

 able length of time on the lead, the distance of the two steel 

 spikes from each other was again determined, and all the dis- 

 placement which had occurred was found to be but o'oi mm., 

 an amount which might very well have been caused by differences 

 of temperature. At all events it was so trifling, that in the case 

 of a pressure three times less, such as would be that of the large 

 lead mi'S utilised in the quantitative experiment, no deformation 

 due to its own weight was to be apprehended. — Dr. Konig 

 further reported on measurements of colour-sense and visual 

 acuteness effected by him on a number of Zulus at present staying 

 in Berlin. Their colour-sense was tested by means of the leuco- 

 scope. On the turning of the Nicol prism the savages stated 

 distinctly that the colours of the two images became even more 

 similar to each other, and at last almost alike, and that, on a 

 further turning of the Nicol prism, the colours came to vary 

 more and more from each other. The colour-sensibility of the 

 savages was, therefore, equal to that of the normal eyes of 

 civilised peoples. They distinguished with exactness, and de- 

 noted by different names the colours red, yellow, blue, brown, 

 black, and white. While they distinguished as red only the 

 purest spectral red, they denoted as yellow or as blue all objects 

 having any yellowish, or, on the other hand, any bluish tinge. As 

 "grass colours " they called the green, and violet they named after 

 a mineral unknown to Dr. Konig. The unsaturated colours they 

 defined by affixing a syllable to the name of the particular 

 colour in each case, an affix signifying much the same as 

 "young." The visual acuteness was measured by means of 

 Snellen's writing tests, according to which the smallest cha- 

 racters used, when distinctly seen at a distance of 6"5m., was 

 equal to I. From extensive statistical investigations in Germany 

 the visual acuteness of a perfectly normal eye was found to 

 average 1 "75- The measurements taken with male Zulu adults 

 showed, on the other hand, that they were able to recognise 

 with certainty the smallest written characters at a distance of 

 from 24 m. to 25 m. ; a Zuly boy of about eight years showed a 

 visual energy of only 1 '50 ; and a Zulu woman a still lower value 

 of visual force — a result which was, however, to be explained by 

 the circumstance that the woman was squint-eyed, and had, 

 moreover, clearly-ascertained obscurations of the cornea.— Fol- 

 lowing up this address, Dr. Konig intimated that, in the 

 Physical Institute, experiments had been made by Dr. Uhthoff on 

 the influence of light intensity on visual acuteness. From a large 

 number of experiments it appeared that if the light intensity was 

 taken as abscissa, and the degrees of visual acuteness appertain- 

 ing to it as ordinates, then the resulting curve, in the case of the 

 greatest visual acuteness answering to a good full illumination 

 by day, ran parallel to the axis of the abscissa, falling, at first 

 slowly and then rapidly, towards the null point. The mode of 

 the sinking of the curve was different with different individuals. 

 Under low light intensities differences occurred as much as 1 to 

 2. The visual energy became null shortly before the light 

 intensity was null. In this respect likewise, however, there 

 were differences in the case of different individuals, those pos- 

 sessing a greater acuteness of vision showing the visual energy 

 at the null point under a greater light intensity than in the case 

 of such persons as had a lower acuteness of vision, in whom the 

 curve began nearer the null point of the abscissa. Normal eyes 

 with greater acuteness of vision, under the highest light intensi- 

 ties attainable by means of a petroleum lamp, showed symptoms 

 of dazzlement, and the curve sank to the axis of the abscissa. In 

 the case of the eyes of much less visual acuteness the curve, even 

 under these highest intensities, continued still parallel to the 

 abscissa. In the discussion which this address gave rise to, 

 Prof, von Helmholtz brought out and established, by entering 

 into detail, that it was altogether unjustifiable to assume that the 

 ancients had not such developed colour-sense as recent per- 

 sons, and that this assumption was an inference quite unwarrant- 

 ably drawn from the mere defect of names for the different colours. 



February 20. — Dr. Kayser referred to a method published 

 by M. Wolf in the Comptes Rendus for measuring the 

 velocity of light, which differed from Foucault's experi- 

 ment inasmuch as the rotating mirror was concave and the 

 aperture admitting the light was a small transparent spot in a 

 larger concave mirror. By Wolf's method the displacement of 

 the reflection of the light could be made to reach as much as 

 I m., and could be easily measured with precision. — Prof. 

 Neesen made some communications respecting an investigation, 

 which was not yet concluded, into Geissler's tubes. In an older 

 tube with aluminium electrodes he found that the process of 

 evacuation, up to the highest degree of rarefication, at which the 

 electricity no longer passed through the tube, was rendered 

 more difficult if continuous electric discharges were sent 

 through the tube, but, on the other hand, was very easy when 

 no electric current was transmitted. If, with high degrees of 

 rarefication, phosphoric light filled the glass ball, a black pre- 

 cipitate was regularly formed on the glass, which disappeared on 

 the admission of a small quantity of air into the tube. If the 

 tube was put in communication with an electric lamp, and the 

 carbon thread, after being kept in a glowing state for about an 

 hour, was allowed to cool, a complete vacuum was more 

 easily obtained, probably because the gaseous substances ad- 

 hering to the glass were absorbed by the carbon. In such 

 a case it was of no consequence for the evacuation whether 

 a discharge was transmitted continuously through the tube 

 or not. The phosphoric light, after the absorption by the 

 carbon-thread, was likewise changed. Instead of being yellow 

 and filling up the whole ball, it was rosy, limited, and soon 

 disappeared. If the tube was then for some time exposed to the 

 air and evacuated, yellow phosphoric light and the black preci- 

 pitate again appeared. Prof. Neesen was of opinion that the 

 process of phosphorescence was induced by substances which were 

 absorbed by the glass and decomposed by the electric light, and 

 that the black precipitate was a product of this decomposition. — 

 Dr. Sklarck referred shortly to the measurement of the propaga- 

 tion velocity of electricity in telegraph wires, which Prof. 

 Hagenbach, in Basel, had carried out according to a new 

 method. 



CONTENTS Page 



The Debate on Vivisection at Oxford 453 



The Relative Efficiency of War-Ships {Illustrated) 454 



The American Association 455 



Letters to the Editor : — 



On the Terminology of the Mathematical Theory of 



Elasticity. — Karl Pearson 456 



Civilisation and Eyesight. — Col. J. F. Tennant, 

 F.R.S. ; Sydney Lupton ; Major Allan 



Cunningham 457 



The Pupil of the Eyes during Emotion. — Dr. Samuel 



Wilks 458 



Aurorse. — E. Brown 458 



Injuries caused by Lightning in Venezuela. — A. 



Ernst : . . 458 



Mira Ceti.— J. E. Gore 459 



Physical Geography of the Malayan Peninsula. — L. 



Wray, Jun 459 



The Continuity of Protoplasm in Plant Tissue. — 



Thomas Hick 459 



Time in the United States. — E. W. Claypole . . 459 



Facilities for Botanical Research 460 



Molecular Dynamics. By Prof. George Forbes . . 461 

 The Long Durations of Meteoric Radiant Points. 



By W. F. Denning. {Illustrated) 463 



Notes 465 



Our Astronomical Column : — 



Tempel's Comet (1867 II.) 468 



The Variable Star Mira Ceti 468 



Astronomical Phenomena for the Week 1885, 



March 22-28 468 



Geographical Notes 469 



Accidental Explosions Produced by non-Explosive 



Liquids. By Sir Frederick Abel, C.B., F.R.S. . 469 

 Programme of Work to be Pursued at the U.S. 

 Naval Observatory at Washington, D.C., during 



the Year beginning January 1, 1885 472 



Scientific Serials 473 



Societies and Academies 473 



