246 



NA TUKE 



[January i i, 1906 



LETTERS TO THE EDITOR. 



[The Editoi do, not hold himself responsible foi opinions 

 expressed by his correspondents. N either can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended foi this 01 any other part of Nature. 

 No notici is taken of anonymous communications.] 



Insectivorous Water-plant from Trinidad. 



Specimens ol the carnivorous water-plant from the 

 Trinidad Pitch Lake, referred to in the note on p. 230, 

 ,,,, been • eel al Kew from Mr. Hart. It is not, 

 however, as supposed, " a species of Nil lla," which is an 

 aquatic cryptogam, but .1 flowering plant, and a species ol 

 Utricularia. 



The habits ol these plants are fully discussed in Mr. 

 Darwin's " Insectivorous Plants." 



VV. T. Thiselton-Di i r. 



The Maximum Number of Double Points on a Surface. 



I 1 is obvious that a surface, like a curve, must have 

 a maximum number of double points; and it is also obvious 

 that all of them may be conic nodes, but only a limited 

 number ol them can be binodes ; but so far as 1 have 

 been able to discover, no formula has been obtained for 

 determining the maximum number. In Hudson's book on 

 " Rummer's Surface," a proof is given that a quartic 

 surface can have as many as sixteen conic nodes, bul no 

 general theorem is alluded to. I shall therefon tati 

 formula b\ means of which the maximum number can be 

 calculated. 



Let a surface of degree 11 and class m have C isolated 

 conic nodes. Let f and i be the number of double and 

 stationary tangents possessed by any plane section of a 

 tangenl cone the vertex of which is an arbitrary point. 

 Then it is not difficult to show that 



m = n(n-i) 2 -2C (1) 

 i = 4»(»-i)(n-2)-6C 



2f={zC-»(»-i) 2 + s( 2 - |«(«-i)(3«- 14) 1 25: (3) 



Now t and 1 must be zero or positive integers ; also 



in must be a positive integer which does not fall below 



a certain limit, and thi se conditions will in general be 



satisfied by taking 



' •"•• i) = + 5=±'-. 

 where ft is the least odd integer the square of which is 

 not less than n(n— i)(3n — 14)4-25. The sign of I; must 

 In determined from the above mentioned conditions, and 

 should the least value of I; fail to satisfy them a greater 

 :,| be taken. A. B. Bassi I . 



January 2. 



Sounding Stones. 



\I\ny hard and compact varieties of rock are son us 



when struck. Flint nodules often possess this property. 

 The purity of the tone appears dependent upon the length, 

 calibre, and homogeneity of the nodule, the besl results 

 being obtained from the long and slender forms. At Stud- 

 land Hay I have collected many of these " musical " Hints, 

 and obtained one from a chalk pit near Faversham which 

 can be used as a gong when suspended. This particular 

 specimen is nearly 2 feet in length (it was once longer), 

 and is scarcely as thick as a rolling-pin ! 



\1 nu years ago I saw a " rock harmonicon " in the 

 museum at Keswick. It was formed of strips of rock 

 (known as " clinkstone, "1 arranged on the principle of 

 tlie dulcimer, upon which various tunes could be played. 



The phonolite of the Wolf Rock, nine miles south of the 

 Land's End, possesses sonorous properties, and Sir 

 YVyville Thomson has described St. Michael's Mount, an 

 island near Fernando Noronha, as being entirely formed 



ol ph (lite which " literally rings like a bell " ..11 being 



struck. 



In quarrying tie- rock from the- Whit Bed, at Portland, 



the workmen profess to be able to judge of the quality 

 of the limestone b\ the clearness of the metallic ring 

 emitted from the blocks on being struck. 

 January 5. Cecil Carus-Wilson. 



Heat a Mode of Motion. 



I'liROUGi Swedenborg's " Principia," published in 



[733, both lieat and light are constantly regarded as 

 ethereal undulations. The definition, of beat a, a rotary 

 movement of minute ether particle, will lie found in 

 part iii., chapter v., No. 21 ; chapter vii., No. 10; 

 chapter viii., No,, s, .,, 10, 10. 



The following is from the " Principia," part iii., 

 chapter vii. : — 



" Whatever the ether presents to our organs by means 

 of colours, the air presents to us by means of modulations 

 and sounds. Thus Nature is always the same, always 

 similar to herself, both in light, and in sound, in the eye 

 and in the ear; the only difference is that in one she is 

 quicker and more subtle, in the other slower and crasser." 



Although this is not an example from the seventeenth 

 century, it anticipates the theories of Rumford and Young 

 a, to light and beat by some sixty years. 



Charles E. Benham. 



Colchester, December 23, 1905. 



The Naming of Colours. 



Perhaps some of your leader, would be interested in, 

 and could suggest some explanation of, the following rather 

 fanciful colour term. A light purple, almost a mauve, is 

 railed by the Chinese ff (sut„) ff- (Ts'eng),' £1 fshik,) 

 " snow green colour." I have asked many educated 

 Chinese for some explanation of the name, but tie besl I 

 can gei i, the Chinese are very " fanciful " in the use 

 of colour terms. 1 may say that the term I have trans- 

 lated " green " is sometime, applied by the Chinese to the 

 colour of the sky. Alfred II. (rook. 



Queen's College, Hong Kong, December 2, 1005. 



observer 



TlIE aurora 

 Szczawnica, ir 

 meteor ilogii a] 

 M.E.T. 



The da\ of November 

 in ( i.dii ia cloudy and r 

 for a while at Szczawnica 

 4S4 metres ; longitude, 20'" 

 I g o N . 



Aurora of November 15. 



of November 15, 1905, was seen at 



(i.dicia (Karpathian Mountain,), bj the 



Mr. Wojakowski at oh. p.m. 



5 and the subsequent night were 



ny. Probably the sky was clear 



The altitude of Szczawnica is 



0' F. of Greenwich ; latitude, 



M. P. Rcdzki. 



NO. 1889, VOL. J T,~\ 



K.K. Sternwarte, Krakau, Januai 



Ascent of Sap in Trees. 

 W1111 reference to an article on the above subject which 

 appeared in your issue of October 20, 1005. the following 

 extract from a paper — which your contributor has doubt- 

 less noi seen, published nearly ten years ago — will prob- 

 ably interest some of your readers. 



Frank Harris. 

 Maryland, Saundersfoot, December 25, 1905. 



Extrai 1 prom Indian Engineering, February S, 1896. 

 Ascent of Sup in Trees. 



Among the various theories which have been advanced 

 to explain the circulation of sap in plants, those dependent 

 on purely mechanical principles are, as has been pointed 

 out, entirely untenable. That hypothesis which relies 

 solely mi tin- osmotic action of the root hairs, though 

 adequate in itself to account for the rise of water to almost 

 any extent, is not compatible with the so-called " negative " 

 pressure observed to exist in the vessels of living timber. 

 Ilie last mentioned among the explanations to which 

 allusion has been made — that which invokes the aid ol 

 what may be loosely described as the vital principle — 

 though unobjectionable in itself, unnecessarily complicates 



