152 



NA TURE 



[DeCEMISEK 19. IQOI 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to lo) respond with the writers of, rejeciei 

 manuscripts intended for this or any other part of Natuke. 

 No notice is tcUien of anonvmous communications.'^ 



Humus as a Preservative against Frost. 



I HAVE just read a French translation, by my old friend 

 Prof. Henry of the Nancy Forest School, of Wollny's classic 

 work on the decomposition of organic matter. In it I find the 

 statement that spring and autumn frosts are dangerous on 

 peaty soils only when the surface of the latter is dry. Wollny 

 gives no illustrations of this law, but I recently observed one 

 in my garden at Coopers Hill. 



Last Septemlier I dug up several rose beds on my lawn and 

 sowed them with grass seed, which has produced a fine crop of 

 young grass. This I carefully watered, and the soil in the beds 

 was well trenched and covered with decomposed leaf mould 

 before the seed was sown. The rest of the lawn has not been 

 trenched, probably for thirty years, and the soil under the grass 

 in it, a stiftish loam, is now singularly dry for the time of the year. 



On the morning of December 6 there was a slight frost, 

 31° F. being registered six inches above the grass. At 8 a.m. 

 the lawn was white with rime, except on the new grass, which 

 remained green. 



This must be due to the fact that the moist, well-trenched 

 humus soil under the new grass was able to conduct heat from 

 below and thus kept the air in contact with it above the 

 freezing-point, while the dry, compact loam under the old turf 

 could not supply sufficient heat to the old grass to preserve it 

 from freezing. Dry humus, according to Wollny, has a low 

 specific heat and is a bad conductor, while wet humus has a 

 high specific heat and is a good conductor of heat. On another 

 occasion, when snow fell, it melted much sooner on the new 

 grass than on the rest of the garden. 



As a further illustration of VVollny's law I may cite the fact 

 that water is let on to cranberry swamps in Carolina when frost 

 is feared during the blossoming period, and also that in norlh- 

 west India, on clear evenings when frost is feared, vegetable 

 gardens and sugar-cane plantations are irrigated in order to 

 obviate danger from frost. 



It is also well known in Germany that if a sphagnum peat 

 bog is to be reproduced, a thin layer of peat must be left at the 

 base of the bog after the upper peat has been removed, and this 

 layer kept carefully under water, as otherwise the drying up 

 and consequent freezing of the peat will kill the moss. 



Slight frosts are very prejudicial to vegetation in sub-tropical 

 forests, and, when frost is imminent, the precaution of trenching 

 the soil, removing weeds and irrigating cultivations is extremely 

 important for young sugar-cane and other crops. 



Coopers Hill, December 8. W. R. Fisher. 



A possible new Petroleum Field near Naples. 



When sailing from Posilipo to Sorrento on August 31 last, at 

 about four or five miles from the nearest land of the Sorrentine 

 Peninsula we encountered a most unmistakable smell of petro- 

 leum, just as if a leaking petroleum tank steamer had crossed 

 our bows a few moments previously. Two tracks of the smell 

 were distinctly noticeable, the one at lat. 40" 41' 30", long. 

 14° 19', and the other at lat. 40' 42', long. 14° iS' 30". A 

 moderate/«ra«o or southerly wind was blowing at the time, so 

 that in all probability the source of the petroleum was somewhat 

 to the south of the position given. 



The only other record of a petroleum source in the immediate 

 vicinity of Naples is that of the Balneum Olii I'etrolei, or 

 bagno del petroico, which formerly existed near the Stufe di 

 Nerone, between Pozzuoli and Baia. This petroleum bath has 

 now quite dried up, but formerly was much praised by medixval 

 writers for its curative powers in cases of leprosy and cholera, 

 and also because its waters caused the limbs of bathers lo 

 rejoice in new found vigour. The last mention of this petroleum 

 bath was by Bartoloin 1679. In the southern Italian provinces 

 petroleum has been found in considerable quantity at San 

 Giovanni Incarico and at Pico in the valley of the Liri in the 

 district of Gaeta. Indeed, in 1878, 600 tons, or almost all the 

 Italian petroleum, came from this source alone. In the last two 

 decades the annual output has much diminished and has become 



NO. 1677, VOL. 65] 



insignificant as compared with the increased production of the 

 wells in northern Italy. Petroleum has also been stated to 

 occur at Tramutola, on the Gulf of Taranto, and asphalt is 

 recorded from the east side of the Abruzzi, about twenty miles 

 from Pescara on the Adriatic (Redwood). 



The depth of the water {80 fathoms) at that part of the 

 Bay of Naples where the smell was noticed is too great for the 

 collection of the petroleum to be commercially practicable. 

 But the long-continued escape of petroleum in the immediate 

 vicinity of the Apennine Limestones of the Sorrentine Penin- 

 sula is an indication that deep borings might be successful and 

 might one day yield as profitable a supply of petroleum as the 

 borings in northern Italy. The petroleum fields of the north of 

 Italy near Bologna and Piacenza extend along anticlinals of the 

 Tertiary Limestone, and therefore are geologically similar in 

 many respects to the country in or near which the newly dis- 

 covered petroleum spring occurs. R. T. GuNTHER. 



Magdalen College, Oxford, December 13. 



Automatic Actions. 



As Mr. Dixon points out (p. 102), a mental process frequently 

 repeated becomes automatic. 



The impulse passes readily along a path in the brain-cells pre- 

 viously frequently traversed by similar impulses, much as a man 

 who revisits the haunts of his youth may, while in a brown study 

 — that is, while abstracting his mind from conscious direction — 

 find his way unerringly through cross-paths, whereas if he had 

 tried to think out his route he would probably have gone astray. 



Mr. Dixon's remarks on the different modes of rising of the 

 horse and cow suggest an explanation. I have hitheito re- 

 garded the explanation as due lo anatomical differences, but the 

 anatomy of animals has been modified by habit and habit by 

 the necessities of environment. 



The horse, which couches on the plain in long grass, rises head 

 first. This method gives him an early view over the surround- 

 ing grass and keeps his hind legs (his chief propellers) well 

 under him. 



The cow, whose natural lair is under low-hanging boughs, 

 rises tail first. This method allows her till the last moment to 

 keep her eyes upon and her horns presented to an approaching 

 foe. W. Benthall. 



December 7. 



VARIATION IN FOWLS. 

 'T'HE rectirrence of the large shows of the different 

 -'• varieties of doniestic poultry which occurs at this 

 season of the year gives an admirable opportunity to 

 those interested in the subject of studying the characters 

 of the different breeds, and the almost inniiiiierable varie- 

 ties produced by crossing thein. The study of variation has 

 been a favourite pursuit of mine for more than half a 

 century. When Darwin was preparing his works on 

 the "Origin of Species" and on the " \"ariation of 

 Animals," he was surprised to find, when I was intro- 

 duced to him by Yarrell at a poultry show, that I had 

 made a large collection of crania of the different varieties. 

 Of these specimens he availed himself lar;.;ely in his 

 work on " \'atiation,'' in which I hail the great pleasure of 

 assisting him. I can, therefore, speak with considerable 

 precision of the great change which has taken place in 

 the breeds of poultry during the last fifty years. The 

 figures in Darwin's large work on the " \'ariation of 

 Animals" were all drawn from birds selected by myself 

 as the most typical specimens of the various races, but I 

 may state that there is not a single figure shown that would 

 not now be repudiated as utterly unworthy of exhibition 

 by the present fanciers, every variety having had its fancy 

 points so greatly increased. To take the figure of the 

 Spanish fowl (shown in chapter vii.), characterised by its 

 white face and large white ear lobe. This represents a 

 fowl which now hardly exists, for the comb has been in- 

 creased to at least four times the area of that shown by 

 Darwin ; the white skin on the face has been so much 

 enlarged as to cause the birds when aged to become 



