384 



NATURE 



\March i, 1877 



The Russian Government having refused to enact a law by 

 which all the kooi-qans, or ancient and prehistoric grave- 

 mounds, so numerous in Russia, would be proclaimfd the pro- 

 perty of the state, a private society is now in way of formation 

 fnr the same purpose. The society proposes to enter into nego- 

 tiations with proprietors of land for receiving from them grants 

 of property on the koorgans, and to undertake afterwards a series 

 of systematical explorations of these mounds. 



The Denver News states that after a severe snowstorm on the 

 night of December 22, 1876, the sun, next morning, rose clear, 

 but the air was filled with particles of frost, the refraction from 

 which caused the appearance of " mock suns" or "sun dogs." 

 First, extending from the sun right and left was a circle entirely 

 around the heavens. Along it were the " sun dogs " in their 

 usual places, with extra ones in the north-west, south-east, and 

 south-west, being directly opposite the sun and at right angles to 

 that line. A very bright circle, like a continuous rainbow, sur- 

 rounded the sun, at an angle twenty or thirty degrees from it, 

 and crossing the horizontal circle at the most brilliant of the 

 false suns. Another and similar circle, and of about the same 

 diameter, occupied the zenith. Thus there was a complete circle 

 around the horizon, and twenty to thirty-five degrees above it 

 two complete rainbow circles of exceeding brightness and seven 

 "mock suns" or "sun dogs." The spectacle lasted, with 

 changing effects, for two hours or more. 



Austrian census statistics show that cretinism is prevalent to 

 a great extent in the more mountainous portions of the empire. 

 The proportion in 10,000 inhabitants is 40 in the Salzburg 

 district, 18 '3 in Upper Austria, 17 in Styria, 10 in Silesia, 76 in 

 Tyrol, &c. As yet no institution has been provided by the state 

 for the reception of the unfortunate victims. 



A SERIES of measurements of the calorific intensity of solar 

 radations and of their absorption by the terrestrial atmosphere, 

 has been lately made by M. Crova. His mode of observation is 

 described in the December number of the Journal de Physique. 

 He has ascertained that the law of transmission of radiations 



may be represented by an expression of the form y= ; — ~ — , b, 

 ' ( I -t- ax) 



in which y represents the calorific intensity of radiations which 

 have traversed an atmospheric thickness equal X.o x ; Q is the 

 so'ar constant which, in the author's experiments, is represented 

 by values generally superior to two units of heat received per 

 minute on a square centimetre ; a and b are two numerical con- 

 stants determined by the position of tangents to the curve drawn 

 at different points. The coefficient of transmissibility of the radi- 

 ations through an atmospheric thickness equal to unity varied, in 

 the circumstances in which M. Crova measured it, between about 

 0'940 and o'8oo, according as the atmospheric thickness already 

 traversed was more or less considerable. 



Mineralogists have often been troubled to distinguish with 

 certainty between apatite and nephelin. A. Streng communi- 

 cates in the last Mineralogischen Mittheilungen, a simple but 

 secure method for overcoming this difficulty. If a drop of a 

 concentrated solution of ammonium molybdate in nitric acid be 

 placed on a thin section of an apatite crystal under a microscope, 

 the observer notices quickly the formation of a circle of small 

 yellow crystals of loM^Og -f P04(NH4)3, either in the form of 

 regular octahedrons or of regular rhombic dodecahedrons. A 

 second test is the following. If a drop of sulphuric acid be added 

 to a section which is already partially dissolved in nitric acid, 

 the formation of crystals of gypsum is easily noticed. Nephelin 

 yields negative results in both cases ; a positive test for its pre- 

 sence consists in the addition of a drop of hydrochloric acid to a 

 thin section under the microscope. After the lapse of a few 

 minutes the formation of numerous small colourless cubes of 

 sodium chloride is quite perceptible. They result from the 



decomposition of the silicate of sodium by hydrochloric acid, and 

 the insolubility in the latter of the salt thereby formed. 



The Bulletin of the Belgian Academy of Science (vol. 42, 

 Nos. 9 and 10) contains the second part of an interesting memoir 

 by M. J. Plateau, " On Accidental or Subjective Colours." The 

 author had advanced, in 1834, a theory for the explanation of 

 the subjective colours, and especially insisted on the circum- 

 stance that, after having looked some time upon a coloured 

 body, we mostly do not see the true complementary colour, but 

 some other : the orange, for instance, instead of a pure yellow, 

 after the blue ; or a violet, instead of the blue, after the yellow. 

 He explained it by supposing, firstly, that the retina, after having 

 received the impression of some colour, comes immediately into 

 such a condition as if it were influenced by the opposite colour, 

 but that this subjective impression soon disappears, and reap- 

 pears again, alternating with reappearing impressions of the 

 primitive colour of the coloured body; and secondly, that similar 

 phenomena take place also in space, i.e., that the image of the 

 coloured body on the retina is surrounded, firstly, by a narrow 

 strip of the same colour as the body (which phenomenon we call 

 irradiation), and then by a strip of opposite colour, around 

 which, under some circumstances, may reappear a third strip, of 

 the colour of the body looked upon. This theory having been 

 much opposed since its appearance, especially in Germany and 

 England, the author now discusses the various objections ad- 

 vanced against it ; those relative to the first part of the theory 

 were the subject of the first part of the memoir {Bulletin, 

 vol. 39, 1875), and those relative to iis second part are 

 dealt with in this second memoir. The author begins his dis- 

 cussion with the objections against his theory of irradiation, 

 dealing at great length with the opinions and objections of 

 Helmholtz, and treating very skilfully the many difficulties of the 

 whole question, among which the various myopy of the observers 

 seems to be an important one. Further, the author criticises 

 the theories of irradiation advanced until now (the imperfect 

 accommodation of the eye, its spherical and chromatic aberration, 

 and the diffraction at the borders of the pupil), and concludes 

 that the fact that two neighbouring irradiations may mutually 

 neutralise each other, would alone be sufficient to condemn all 

 these theories. The memoir is to be continued. 



A COMPARISON has recently been made by Dr. Buff between 

 the indications of the thermomultiplier and the radiometer. The 

 two instruments were placed side by side in the cone of light 

 admitted through an aperture of a board from a gas lamp, 

 which could easily be regulated and kept constant for some 

 minutes. There was a glass disc in front of the thermopile. In 

 the galvanometer the deflections of the needle were proportional 

 to the deflecting force up to 21°. On tabulating deflections and 

 numbers of rotations, it appears that their product is very nearly 

 a constant number, warranting the inference that the velocity of 

 rotation of the little wheel is inversely proportional to the heat 

 action of the penetrating rays. This confirms the view that the 

 turning of the radiometer is due to an action of heat rays which 

 penetrate the glass. "If the radiometer," says Dr. Buff, "is 

 incapable of measuring a mechanical force of light, it none the 

 less wears its present name with full right. It is a special form 

 of thermometer, only exclusively for heat rays of high refrangi- 

 bility, whose heating force is proportional to the velocity of rota- 

 tion of the wheel." 



The additions to the Zoological Society's Gardens during the 

 past week include a Mauge's Dasyure [Dasyurus maugm) from 

 Australia, presented by Mr. Robert S. Craig ; a Slender-billed 

 Cockatoo {Lic7netis tenuirostris) from Australia, presented by 

 Mr. Bartle G. Goldsmid ; a Chilian Sea Eagle {Geranoaeius 

 aguia) from South America, presented by Mr. C. Clifton ; a 

 Levaillant's Amazon {Chrysotis levaillanti) from Mexico, pre- 



