April 25, 1878] 



NATURE 



515 



about the same course as that for'pure water, except that the 

 maximum of density was reached, not at 4°, as in the case of 

 pure water, but under 3°, as is the case with salt substances. 



Recent observations by M. Ebermayer demonstrate (i) that 

 the air in a large forest is in summer nearly twice as rich in 

 carbonic acid as free open air ; {2) that forest ground in summer 

 contains much less CO2 than unwooded ground (the CO2 formed 

 by slow decomposition of humus in the close forest seems mostly 

 to pass into the air, and. is probably utilised by the leaves for 

 assimilation) ; (3) that, with rise of temperature, the increase of 

 CO2 in arable ground is very much greater than in forest ground ; 

 and (4) that the spread and motion CO2 in the ground seems 

 to take place very slowly, for in two places quite near together 

 the amount of CO., may be very different. Among other bear- 

 ings of these facts, the ground covering of a forest can have no 

 important influence on the amount of COj and lime in spring 

 water, and unwooded ground may have a greater action in this 

 respect. Again, animals living underground, e.g. foxes, natu- 

 rally prefer the ground air of the forest, with its little CO a, to 

 to the ground air of the open field, which has much more. 



The influence of concentration of liquids on their electromo- 

 tive force has lately been investigated by M. Moser {Monatsh. 

 der Berliner Acad, der JViss.) who connected two glasses of 

 differently concentrated solutions of the same salt by a siphon, 

 and completed the circuit by wires with electrodes, which were 

 always of the same metal. In all such cases a current arises, 

 passing in the liquid from the dilute to the more concentrated 

 solution, M, Moser used zinc sulphate, nitrate, chloride, and 

 acetate, copper sulphate and nitrate, iion chloride, silver acetate 

 and nitrate, and other salts. The highest electromotive force 

 was I Daniell, and was got with very dilute and concentrated 

 zinc chloride solution. The various effects are arranged in 

 tension-series. By the currents referred to, metal is dissolved in 

 the dilute solution, separated out in the concentrated one. The 

 equivalent of the work done by the current, M. Moser considers, 

 is the work of attraction force between the salt and the water. 

 The current is to be regarded as a reaction current against pas- 

 sage of the ions, as the polarisation current is the reaction current 

 against the decomposition current. 



The subject of acoustic repulsion continues to be studied by 

 M. Dvorak (IVied. Ann., No. 3). Among other things he 

 constructs an acoustic reaction wheel and an acoustic torsion 

 balance. The former consists of four light paper or glass reso- 

 nators placed tangentially at the four ends of two thin cross-bars 

 of wood, pivoted at their intersecting point by means of a glass 

 cap. The mouths of the resonators are all in the same relative 

 position. The wheel is placed before the open end of a tuning- 

 fork resonator, and enters into rotation when the fork is sounded. 

 In another case the sound from the large resonator is transmitted 

 through a conical tube beyond whose thin end is a wheel with 

 square pieces at the end of the cross-arms. In the acoustic 

 torsion balance a wooden bar furnished with a resonator is 

 hung by a wire (as in Coulomb's balance) within a case, which 

 has on the resonator side an opening for admission of sound. 

 By repulsion of the resonator the strength of tones of the same 

 number of vibrations may be compared. 



Lecturing at the Sorbonne -lately on atmospheric electri- 

 city, M. Mascart sought to reproduce the phenomena of 

 thunderstorms. The dull explosions of thunder and the 

 f ulgurations in the heart of clouds preceding fulminant discharges, 

 as also the latter, were imitated by means of a powerful Holtz 

 machine, charging batteries, and condensers suitably aiTanged. 

 The singular movements of thunder-clouds, which, obeying 

 electric attractions and repulsions, are often observed to move in 

 the atmospheric ocean in counter-currents, were illustrated with 

 the aid of a balloon of hydrogen gas, to which was nnpeided a 



piece of metallic wire. The weight of the wire was mch that 

 the small aerostat, rendered slightly heavier than the displaced 

 air, would descend ; biit when it was electrified, it rose t^n, 

 as if freed from its burden. M. Mascart did not attempt an 

 explanation of this curious phenomenon, which has not been 

 repeated since the time of van Marum. 



In a recently-published report by M. Kellner to the Natur- 

 forschcr Versammlung at Munich, he describes experiments 

 made along with some others on an eleven-year old Wallachian 

 hor.se of 434 kilo, weight, with regard to the relation of work 

 done and decomposition of albumen. In five successive periods 

 of thirteen to fourteen days the animal was fed with 5 k. 

 meadow-hay, 5 k. oats, and i"5 k. chopped wheat straw, and 

 did work to the extent of 500,000, 1,000,000, 1,500,000, 

 1,000,000, and 500,000 kilogrammctres in the five periods re- 

 spectively. In periods I. and V. the work done was the same, 

 in II. and IV. doubled, and in III. tripled ; in II. and III. the 

 course was doubled and tripled, and in IV. the weight doubled. 

 Of the dry substance of the fodder were digested in period I. 56*53 

 per cent., II. 56-45 per cent.. III. 56*49 per cent., 1V.54-OI 

 per cent,, V. 53-07 per cent. The horse's weight varied as 

 follows :— I. 534-1, II, 529* I. Ill- 522-3, IV. 508-8, V, 518 

 kilo. The excretion of nitrogen was on an average of 

 the last six to nine days of each experimental series, I. 98-81 k., 

 II. 109-16, III, Ii9*82, IV, 107-53, V. 101-88, These 

 numbers show strikingly, in opposition to Volt's and Petten- 

 kofer's results, that with increase of work done, is associated a 

 not inconsiderable increase of decomposition of albumen. 



The additions to the Zoological Society's Gardens during the 

 past week include an Indian Leopard {Felis pardus) from India, 

 presented by Major Tubbs ; a Red Deer [pervus elaphus), a 

 Common Fox {Cams vulpes), European, presented by Mr. 

 Carroll W. Ansdell ; two Spotted Ichneumons {Herpestes auro- 

 punctatus) from Nepal, presented by Mr. J. Mcintosh ; a Smi- 

 cate {Suricata zenik) from South Africa, presented by Mr. Percy 

 Howard ; an Azara's Fox {Canis azard) from Brazil, presented 

 by Dr A. Stradling; a Stanley Crane (7V/m//^0'^ /«r«^"^a) 

 from South Africa, presented by Capt. A. F. Lendy ; a Lead- 

 beater's Cockatoo {Cacatua leadbeaieri) from Australia, presented 

 by Mr. W. Ruston ; a Collared Fruit Bat {Cynonycteris collaris), 

 four Common Foxes {Canis vulpes), born in the Gardens. 



THE DETERIORATION OF OIL PAINTINGS^ 



11, 

 T F we compare the pictures of the Italian and Dutch schools of 

 J- the fifteenth, sixteenth, and seventeenth centuries, with those 

 of the French and English schools of the last hundre<l year^-;e 

 are struck by the great difference m the nature of their diseases. 

 We may divide thSse diseases into consHiuJioml ones-that is to 

 say S as are based on the method and the material used for 

 Sdn'; and into those produced by external influences. 

 ^ The Dutch pictures of the fifteenth, sixteenth, and seventeenth 

 ine iJurcnpu-u nictures of the fifteenth and sixteenth 



cen uries, and the J^f ^^^J "^^ee '^^^^ constitutional diseases. 

 Tf-^rivrTheseveSSnth century that the Italian pictures 

 l:iT^l.?loS^Zl alteratSn. caus^ by the practice 



^'it SSof thilast hundred years of the French school 

 inc pitiuK^ school, and some painters of other 



substances A3 W. »h=n pulverised «"^, 'XSTrth cS 

 air, loses its transparency, and water, "t'° """"l "'l°!h 

 . P.p„ ,..d a. .h. R~.l In«;.»t;on. Frld.y March .. by R. I.Ar.xh, 

 M.D., MR-C-S.>M.R.l. Contmuwl Prom F, 4?5- 



