526 



NA TURE 



[April I, 1886 



constitute colour-blindness, since the want of appreciation of any 

 colour is but very partial. They next describe observations 

 made by four colour-blind persons, and show that there is a 

 remarkable divergence in their curves from the normal. The 

 deficiency curves are shown, from which it appears that two of 

 the observers are totally blind to red, whilst the other two are 

 partially so. They then show that such observers would not 

 "■ive a true value for any light which is not of identically the 

 same colour as the comparison light they might employ. It also 

 appears that the intensity of illumination felt by a colour-blind 

 is really less than that perceived by a normal-eyed person. 



Two examples of the curves for sunlight are then given, one 

 taken on a day in July by the method of separating close lines 

 by varying the illuminaiion, and the other in November by the 

 method described above. Their results are compared witli 

 Vierordt's curve, obtained by extinguishing colour with while 

 light. 



In order to ascertain the effect of the turbidity of a medium 

 through which light passes (for instance, of air on sunlight), the 

 authors compared the intensity of the spectrum after passing 

 through clear water and turbid water, and found that the absorp- 

 tion agreed with Lord Rayleigh's theoretical deductions that 



I' =l,,.-''-^-'' 

 where I' is the intensity after passing through a turbid medium. 

 Id the intensity after passing through clear water, x the thickness 

 of the turbid layer, k a constant independ'ent of A, \ being the 

 wave-length. 



The authors conclude their paper with a discussion of the 

 intensity curves of the spectrum of carbon filaments electrically 

 heated. 



Chemical Society, February iS. — Dr. Hugo Miiller, 

 F.R.S., President, in the chair. — The following papers were 

 read : — The constitution of undecylenic acid as indicated by its 

 magnetic rotation ; and on the magnetic rotation, &c., of mono- 

 and di-allylacetic acids and ethylic diallylmalonatc, by W. H. 

 Perkin, F.R.S. — Reactions supposed to yield nitroxyl or nitryl 

 chloride, by W. Collingwood Williams, B.Sc. — The condition 

 of silicon in cast iron, by A. E. Jordan and Thomas Turner. — 

 Certain aromatic cyanates and carbamates, by H. Lloyd Snape, 

 B.Sc. — The oil obtained from lime-leaves, by Francis Watts. 



March 4. — Dr. Hugo Muller, F. R.,S., President, in the chair. 

 — A new element : germanium, by Clemens Winkler. — The 

 influence of temperature on the heat of chemical combination, 

 by S. U. Pickering. — The salts of tetrethylphosphonium and 

 their decomposition by heat, by Prof. E. A. Letts and Norman 

 Collie, Ph.D. — The formation of acids from aldehydes by the 

 action of anhydrides and salts, and the formation of ketones 

 from the compounds resulting from the union of anliydrides and 

 salts, by W. H. Perkin, F.R.S. — A new method of preparing 

 tin tetrethide, by Prof. E. A. Leits and Norman Collie, Ph.D. 

 —Contributions to the history of cyanuric chloride, by Alfred 

 Senier, M.D. — The action of naphthylamine on cyanuric 

 chloride, by Harold H. Fries. — Sulphine salts containing the 

 ethylene radicle; part i., diethylenesulphide-melhyl-sulphine 

 salts, by Orme Masson, M.A., D. Sc. — Sulphine salts containing 

 the ethylene radicle ; part ii., on Dehn's reaction between ethyl- 

 ene bromide and alkyl sulphide, by Orme Masson, M.A., D.Sc. 



Zoological Society, March 16. — Prof. W. H. Flower, 

 F.R.S., President, in the chair. — Mr. F. D. Godman, F.R.S., 

 exhibited some examples of a butterfly, Danais plcxippus, from 

 various localities, and made remarks on its distribution, which 

 of late years seemed to have become very widely extended. — 

 Prof Bell made some remarks on the Balanoglossus recently 

 discovered in the Island of Herm, Channel Islands, of which 

 he had exhibited a specimen on a former occasion. — A commu- 

 nication was read from the Rev. H. S. Gorman, F.Z.S., con- 

 taining descriptions of some new genera and species of Coleo- 

 ptera of the family Endomychida: from various localities. — A 

 communication was read from Dr. R. J. Anderson, F.Z.S., of 

 Queen's College, Galway, containing observations on the pelvi- 

 sternum in certain Vertebrates. — Prof F. Jeftrey Bell read a 

 paper on the generic characters of Planarians, basing his obser- 

 vations mainly on a specimen of a Planarian recently found 

 living in this country, and believed to be referable to Bipabutn 

 kt-vense. — Mr. F. E. Beddard read a note on the structure of a 

 large species of earthworm from New Caledonia, of which ex- 

 amples had been recently received from Mr. E. L. Layard, 

 F.Z.S., H.B.M. Consul for New Caledonia. 



Physical Society, March 13. — Prof. Balfour Stewart, 

 President, in the chair. — Prof. U. S. Pickering and A. C. 

 Hayward were elected Members of the Society. — The following 

 communications were read : — On the growth of filiform silver, 

 by Dr. J. H. Gladstone. It has long been known that if a 

 piece of metallic copper be placed in a solution of nitrate of 

 silver, replacement of one metal by the other will take place, 

 the silver being deposited in the crystalline form, sometimes 

 having a resemblance to fern-leaves, or as superposed hex.agonal 

 plates, or knobs. It was observed, however, as far back as 

 1872, by the late Mr. Tribe and the author, that if nitrate of 

 silver were decomposed by suboxide of copper instead of the 

 metal, the silver presented itself in threads, which rarely, if 

 ever, bifurcate, but frequently turn at sharp angles or twist in 

 every direction. This was described in the British Association 

 Report for 1 872, and it was observed that the same forms 

 occurred in native silver. More recent observations have shown 

 that the particular character and rapidity of formation of these 

 thi'eads depend very much upon the strength of the solution and 

 the condition of the suboxide. Hydrated suboxide will scarcely 

 decompose a 2 per cent, solution, even after standing. The 

 threads, which bend at a sharp angle, usually do so at 60° or 

 120°. Other threads, however, are symmetrically curved ; but, 

 especially in strong solutions, they are given to twisting about in 

 every direction, and generally terminate in irregular knobs of 

 silver. As a rule a thread continues to grow of the same thick- 

 ness as it commenced, but it sometimes enlarges for a while into 

 a flat plane, or becomes incrusted for some distance with small 

 crystals of silver. When the solution is very nearly exhausted 

 of silver, fine arborescent forms appear ; but with the suboxide 

 there are never produced the fern-leaved forms, or hexagonal 

 plates, or the other distinctly crystalline structures which charac- 

 terise the growth from metallic copper. During the reaction the 

 suboxide is changed into black protoxide and metallic copper, 

 which dissolves ; and the change will take place as well with 

 the acetate and sulphate as the nitrate. If a mixture of suboxide 

 and metallic copper be employed, not only do the distinctly 

 crystalline and the filiform forms make their appearance, but 

 strange inte: mediate forms come into existence. — Apparatus for 

 measuring the electrical resistance of liquids, by Prof. Reinold. 

 The apparatus consists of two bottles connected by a horizontal 

 tube. The whole is filled with the liquid to be examined, and 

 immersed in water, by which means, and by thermometers 

 inserted in each bottle, the temperature may be regulated and 

 accurately ascertained. The electrodes ai-e platinum plates, one 

 dipping into each bottle. Two fine tubes terminate near the 

 ends of the connecting-tube, and electrodes are fitted into them 

 at some distance from the ends ; by connecting these to a 

 quadrant electrometer or a condenser and galvanometer, the 

 difference of potential between the ends of the tube can be com- 

 pared with that at the ends of a known resistance in the same 

 circuit. — On chromatic photometry, by Capt. Abney and Lieut. - 

 Col. R. Festing. (This paper had been previously communi- 

 cated to the Royal Society.) A series of experiments have been 

 made by the authors to determine the comparative luminous 

 effect of different parts of the spectrum. A monochromatic 

 light from any part of the spectrum of the electric arc was 

 obtained by a method devised by Capt. Abney, and pre- 

 viously described by him to the Society [Physical Society, 

 June 27, 1885, Nature, vol. xxxii. p. 263]. The photo- 

 metric effect at different parts of the spectrum was com- 

 pared with that due to a candle at different distances by 

 Rumford's photometer. In using this it was found best to place 

 the candle in a given position, and obtain a balance by moving 

 the slide upon which the spectrum was formed, and through a 

 slit in which part of the light was allowed to pass rapidly to and 

 fro. For each position of the candle there are thus two corre- 

 sponding positions of the slit. From the results of these obser- 

 vations a curve may be drawn, showing the luminosity at differ- 

 ent points. From the method by which it is obtained it is 

 evident that the curve of one observer is not directly comparable 

 with that of another, since a deficiency of perception in any 

 part of the spectrum would affect the light of the candle as well 

 as that examined. Since, however, the curves obtained by a 

 great number of persons coincide very closely « ith those ob- 

 tained by the authors, they have felt justified in adopting them 

 as the normal curves. In the case of the electric arc the normal 

 curve attains a maximum rather nearer the red end of the spec- 

 trum than the blue. Assuming the normal curve, any other 

 curve may be compared with it by increasing or decreasing its 



