530 



NATURE 



[October 27, 1910 



obvious explanation of them, and has found, not only no 

 sign of any deliberate mutilation, but overwhelming 

 evidence of the reality of the ancient Egyptian's profound 

 reverence for the bodies of his dead relations, and of his 

 horror of mutilating them, even for the purpose of making 

 the incisions necessary for embalming. 



Since this correspondence began, a full discussion of all 

 the data relating to the subject under consideration has 

 been published in the report for 1907-8 on the Archieo- 

 logical Survey of Nubia. There the facts will be found 

 recorded for the use of anyone interested in the matter. 



G. Elliot Smith. 



Effect of Heat on Soils. 



Mr. a. D. Hall in his opening address to the Agri- 

 cultural Sub-section of the British .Association at Sheffield 

 mentioned " a process of heating the soil before sowing " 

 and " a process of firing the soil preparatory to sowing 

 the crop," both of which seem very similar to " burning 

 hush " as practised in the West Indies. On reading 

 Russel and Hutchinson's paper on " Partial Sterilisation 

 of Soil " in Journ. Agric. Sci. for October, 1900, it struck 

 me that their work afforded a probable explanation of 

 " burning bush," and I now make the suggestion in the 

 hopes of obtaining some evidence. The process seems to 

 be similar to that known as chcna in Ceylon, ladang in 

 Malaya, and jhuming in India (see J. C. Willis, "Agri- 

 culture in the Tropics," pp. i and 2), and perhaps some- 

 one with experience of the East could throw further light 

 on the question. 



It is a common practice in Trinidad for a small culti- 

 vator to rent a piece of abandoned land, which is cleared 

 by burning the " bush " in the dry season. In the wet 

 season the clearing is generally planted with maize, which 

 is usually followed by cassava, yams, tanias, &c. In a 

 few years the cultivation is no longer remunerative, and 

 the land, once abandoned, quickly goes back to " bush." 

 One explanation is that the ashes of the burnt " bush " 

 supply a certain amount of mineral plant food in a readily 

 available form (the nitrogen in the plants burnt would, of 

 course, be lost). This plant food would presumably pro- 

 duce an increased yield, but the effect would not last many 

 years. .Another — and I think a more probable — explana- 

 tion is that the burning results in a partial sterilisation of 

 the soil, with a greater production of ammonia. The fact 

 that maize is the first crop grown after the " bush " has 

 been burnt is significant, since it is a crop which is 

 benefited by a nitrogenous manure. 



C. Harold Wright. 



Government Laboratorv, Trinidad, B.W.I., 

 October 8. 



The Colours and Spectrum of Water. 



A perusal of the articles which have appeared in your 

 journal on this subject (Nature, vol. Ix.x.xiii., pp. 48, 68, 

 188, 487, and vol. Ixxxiv., p. 87) leads me to ask if the 

 spectrum of water has ever been thoroughly investigated. 

 It is difficult to believe that this has not been done, and 

 yet there is but little allusion to the important bearing 

 the character of the spectrum must have upon the colour. 

 I should be glad to learn what is the origin of a feature 

 I have sometimes observed in the spectrum, as seen with 

 a " miniature spectroscope " by Browning. This is a dark 

 band or line at about wave-length 6000, which I noticed 

 in June, 1887, in Sark, in clear water, both in the sea 

 and in fresh water. The latter was bluish-green, and the 

 sea was green. .So far as this line would have any 

 influence on the colour of the water, it would tend to 

 make it blue ; but the colour would be much more 

 influenced by the very strong general absorption in the 

 whole of the red and orange beyond the dark line. In 

 the sea water this general absorption extended more feebly 

 to the D line of the solar spectrum, and even to the dry- 

 air band 5. 



In the deep green water of Lago Magglore the spec- 

 trum was almost identical with that of the sea at Sark; 

 I made the wave-length of the dark line about 6050. 



The Lake of Geneva is noted for the deep blue of its 

 NO. 2139, VOL. 84] 



clear water. In it I failed to see the dark line, but the 

 general absorption of the red end of the spectrum was 

 very striking. 



The bluest water I ever saw — bluer than the Mediter- 

 ranean, Red Sea, or Indian Ocean (I have not been to 

 Capri) — was, however, the Blaue See, near Kandersteg, 

 and the Lago di Garda. In the former, pieces of pot at 

 the bottom appeared pure Prussian-blue. During a stay 

 of a few days by the Lago di Garda I could not make out 

 the law of its changes in apparent colour, but at times 

 it was far bluer than the bluest sky I ever saw. It 

 usually had a slightly greenish tinge. Both these lakes, 

 are extremely clear. I regret not having observed their 

 spectrum. T. \V. Backhouse. 



West Hendon House, .Sunderland, October 19. 



Luminous Paint. 



Mr. C. a. Emery, of Marlborough College, has directed 

 my attention to a passage in Livy (xxxix., 13) where the 

 following occurs : — 



" -Matronas Baccharum cum ardentibus facibus decurrcre 

 ad Tiberim, demissasque in aquam faces, quia vivum 

 sulphur cum calce insit, Integra flamma efferre." 



This he renders : — 



" The Bacchantes would run down to the Tiber with 

 burning torches, and plunging them into the water would 

 take them out with the flame unextinguished, because they 

 were covered with a mixture of living sulphur and lime." 



The expression " vivum sulphur " is thus explained by 

 Pliny :— 



" In Italia quoque invenitur sulphur. Genera quatuor : 

 vivum, quod Graeci apyron vocant, nascitur solidum, hoc 

 est, gleba : quo solum ex omnibus generibus medici 

 utuntur. Solum (cetera enim liquore constant, et con- 

 ficiuntur oleo incocta) vivum effoditur, translucetque, et 

 virct." — Plinii Hist Nat. Lib., xxxv., 50. 



It would seem, therefore, that calcium sulphide W'as 

 discovered, and its luminosity observed, about nineteen 

 hundred years before Marggraf, who in 1750 a.d. pre- 

 pared the substance by " calcining gypsum with com- 

 bustible matter." Eighteen years later Canton obtained 

 the same effect by " igniting calcined oyster-shells with 

 sulphur." (Inverted commas from Roscoe and Schor- 

 lemmer's " Treatise on Chemistry," under " Calcium and 

 Sulphur.") 



As neither of these manufacturing methods is difficult, 

 it seems reasonable to suppose that one or other might 

 have been known in Livy's day, and from the Latin text 

 a modification of Canton's method seems probable. 



Except for the above, I can find no direct reference to 

 the discovery of calcium sulphide. 



I noticed when reading Charles Reade's novel " The 

 Cloister and the Hearth " that one of the more strikinjj 

 incidents depended on the use of a phosphorescent pai'il. 

 .As this powerful story is of the fifteenth century, I con- 

 sidered the phosphorescent paint an anachronism, for 

 Brandt is said to have discovered phosphorus in 1669, and 

 the " Bologna stone " (barium sulphide) was discovered 

 only a few years earlier. But Reade may have been 

 aware of the passage in Livy or may have known about 

 Pliny's " Pholas " — the rock-boring mollusc (Piddock) — 

 the phosphorescence of which is said to remain long after 

 death. 



Possibly some readers of Nature may be able to throw 

 more light on the origin of " luminous paint." 



R. G. Durrant. 



The College, Marlborough. 



Velocity of Negative Ions in Hydrogen at Atmospheric 

 Pressure. 



Some time ago Prof. Chattock and I attempted to 

 measure the velocity of the ions from a point discharging 

 in pure and impure hydrogen at atmospheric pressure by 

 the wind-pressure method, in the hope of finding that the 

 negative ion was influenced by the presence of small traces 

 of oxygen. The results were given in Phil. Mag., April, 

 in which it was show'n that the change which the com- 



