2SS 



NA TURE 



\yan. 2 1, uS86 



a coefficient of absorption almost erual to zero. When now 

 light passed through a mixture of chlorine and hydrogen, a part 

 of the light was, in the first place, absorbed by the chlorine, 

 just as though this gas weie the only element through which it 

 passed, and in all probability this absorbed amount was trans- 

 formed into heat. In addition to this effect, on the other hand, 

 the chemical affinity of the gases got excited, and in order to 

 this operation light was likewise absorbed. Whether in this 

 process we had a direct action nf light-r.-tys transformed into heat 

 or only a kind of releasing influence on the part of the rays was 

 a point that had yet to be determined. The difficulty of this 

 determination was enhanced by the fact of the induction which 

 Bunsen and Roscoe had already ascertained, in accordance " ith 

 which the chemical combination of the chlorine with the hydro- 

 gen did not take place at once, but only a longer or shorter time 

 after the beginning of the irradiation. By taking the gas-layer 

 of great thickness Dr. Princ;sheim was enabled to augment 

 the time of the induction to twenty minutes, and the combination 

 of the two gases w.as effected only in the twenty-first minute of the 

 irradiation. For his experiments Dr. Pringsheim made use of a 

 gas-developing apparatus in which concentrated hydrochloric aciil 

 underwent electrolysis by means of iridium electrodes, and from 

 which the gases passed through a tube into a globular irradiation 

 space whence a capillary, divided into millimetres, led to a vessel 

 filled with water, from which, again, a thread of water penetrated 

 into the capillary, and so served as index of the gas-pressure obtain- 

 ing in the .apparatus. Any heating influence expanded the gases 

 and pushed the index outwards while as often as hydrochloric 

 acid was formed— the acid being at once absorbed by the water 

 that was present in the insolation-globe — it caused an advance of 

 the index, and the measure of this advance served as a criterion 

 of the amount of acid formed. Experiments were next instituted 

 in regard to the nature of the induction, and investigation was 

 made as to whether it were identical with the chemical action o( 

 the light or were somewhat different from it. Sources of light 

 of dilTerent intensity and difierent colour were examinetl in 

 respect of their chemical and their inductive action, an<l it 

 always turned out that the rays of most intense chemical action 

 produced likewise the greatest induction. In the measurements 

 of the chemical action of light, which were then taken in hand, 

 a petroleum lamp was used as a source of light, the warm rays 

 of the petroleum lamp being eliminated by means of an interca- 

 lated layer of water. Dr. Pringsheim first observed a sudden 

 movement of the index outwards, which was at once followed 

 by a speedy retirement to the initial position, and from this point 

 the index was then observed proceeding slowly inwards, in pro- 

 portion as muriatic acid was formed and absorbed. Seeing the 

 first movement of the index might be interpreted as an effect of 

 heat, control experiments were instituted with momentary illu- 

 mination, at first by dropping a dark screen with small slit before 

 the flame, and then by means of electric sparks. Each time now 

 that the light ray struck the chlorine hydrogen gas mixture, the 

 index was seen pushing suddenly outwards, and then as suddenly 

 reverting to its former position, whence it then slowly retired 

 inwards. Thei'e could, therefore, be no question in this case of 

 any heating, but there must, on the contrary, be some other 

 cause in operation, to the determination of which other experi- 

 ments should be devoted. — Dr. Konig spoke on colour-blindness, 

 and, in particular, on the important light it would throw on the 

 theory of colours if, in addition to cases of red and green blind- 

 ness, the existence of violet blindness could be demonstrated. 

 Hitherto violet-blind persons had been described only by Herren 

 Donders and Holmgren. The^e gentlemen had examine.! ab- 

 normal eyes, which, in the spectrum bi-tween red and green, 

 saw a circumscribed gray band, exactly at the spot where, 

 in the case of the violet-blind, the two remaining curves of 

 colour sensitiveness intersected each other. Last year, for the 

 first time, Dr. Konig had an opportunity of examining an in- 

 telligent boy of from thirteen to fourteen years of .age, who 

 likewise testified to a quite distinct gray band in the spectrum 

 between green and red, while he saw all other colours accurately. 

 The belief that here was a case of a violet-blind person was, 

 however, materially shattered when the spectral violet was pre- 

 sented quite pure .and isolated before the boy. He then said he 

 saw a colour which he had never before seen in his life. The 

 boy was, therefore, not incapable of perceiving violet rays. 

 Later, Dr. Konig had occasion to examine an eye affected with 

 central turbidity of the retina, an eye which — so far as the ex- 

 periments that were capable of being executed only with great 

 care, allowed the determination of the matter — was, in point of 

 fact, violet-blind. On investigating the neutral point, it was 



found with very great precision at the wave-length, 56o'i4. Ac- 

 cording to theory, the intersecting point of the red and green 

 curve lay at 563"5 wave-length, very fairly, therefore, in agree- 

 ment with the value thus found. The measurements of intensity 

 between the wave-lengths 560 and 470 yielded values wdiich like- 

 wise coincided exactly with th ise given theoretically for bichro- 

 matically violet-blind eyes. 1 he now considerably more exact 

 method for examining the colour-blind .and the significance of 

 these astert.ained facts in relation to the theory would be set 

 forth by Dr. Konig on a future occasion. — In the discussion 

 which the first commimication called forth. Prof. Landolt made 

 the proposal of using a solution of lithium chloride in order to 

 obtain, by way of electrolysis, a perfectly pure chlorine hydrogen 

 gas mixture. In the case of electrolysis of hydrochloric acid there 

 was a danger, he represented, of oxygen being united with the gas 

 mixture. Prof, von Helmholtzsaid th.at the influence of the-rays 

 of light on the chlorine and hydrogen molecules might be conceived 

 by supposing that they acted in a manner similar to that of elastic 

 balls executing oscillations in a high-'-tanding fl.at vessel, where- 

 by they were continually passing up and down. Did one ball 

 receive on some occasion or other a stronger impulse than usual, 

 then it leaped over the edge .and fell to the ground ; so that in 

 respect of the totality of movements in the vessel, a part of the 

 energy was lost. In the same way, when an atom of chlorine 

 and hydrogen .approached so close to each other that they united 

 chemically, a part of the energy of the oscillations of light 

 became lost. In reference to the second communication (that of 

 Dr. Konig), Prof, von Helmholtz set forth the difficulties of in- 

 vestigations of the kind in question, and laid special stress on a 

 psychological difficulty. It was known that only the central 

 part of the retina was trichromatic. With the part of the retina 

 attaching itself peripherically, only two colours were seen, while 

 the extreme region of the retina was monochromatic. Never- 

 theless, we always saw a white surface as white, whatever part 

 of the retina were struck by these rays. It was plain that we 

 had learned by experience to perceive objects that appeared 

 white in the central field as white likewise when at the periphery 

 they stimulated only two or but one kind of fibres. In all in- 

 vestigations into colour-blindness this psychological point was 

 one which ought to be taken into quite material account. 



CONTENTS Page 



The East Anglian Earthquake of 1884 265 



Systematic Small Farming 266 



Our Book Shelf:— 



Hatton's " North Borneo " 267 



Letters to the Editor : — 



On "Seter," " .Strandlinjer," or Parallel _Roads in 



Centi'al Norway. — Dr. Andr. M. Hansen . . . 268 



The New Star near x' Orionis. — Prof. A. Ricco . 269 



Anchor Frosts, — Dr. John Rae, F.R.S 269 



The Dover Boring. — William Whitaker .... 269 



The Viper and its ^'oung. — A Creole ...... 269 



White Blackbirds.— A. S. Mathews ..... 269 



Curious Phenomenon in Cephalonia. — R. S. Newall, 



F.R.S 270 



After-images. — ^J. C. S 270 



Professor Tait on the Partition of Energy between 



Two Systems of Collidmg Spheres ....... 270 



Report to the Trinity House on the Inquiry 

 into the Relative Merits of Electricity, Gas. and 



Oil as Lighthouse llluminants 271 



Geographical Education 273 



Hunter's House. By Dr. B. W. Richardson, F.R.S. 



(Illustrated) 275 



The Meteor Shower at the Mauritius. By C. 



Meldrum, F.R.S '^ 276 



Notes 276 



Our Astronomical Column : — 



Comet Brooks 279 



Astronomical Phenomena for the Week 1886 



January 24-30 279 



Geographical Notes 280 



The Benefits which Society Derives from Uni- 

 versities. By D. C. Gilman, President of the 



Johns Hopkins University 2S1 



Prjevalsky's Explorations in Central Asia 283 



University and Educational Intelligence 284 



Scientific Serials 284 



Societies and Academies 285 



