June 1 8, 1874] 



NATURE 



125 



p. minus, though the former is much the larger. Such then are 

 the facts as they appear from Cuvier's writings. The fact that 

 this one sI<eleton of P. niiiuis was found witli the neck in the 

 erect position may have been considered by Cuvier as hardly a 

 sufficient reason for placing the neck of his restored specimen, 

 which showed so many tapiroid peculiarities, in the same position. 

 Now, however, that a second skeleton of a PaUtothcriiim has 

 been found, with the neck in a similar position, the probability 

 that such a position is the natural one is immensely enhanced. 



Two points, however, remain somewhat involved in obscurity ; 

 first, hovvis it that the skeleton of /'./wa^'w/Mjas found at Vitry-sur- 

 Seine the other day, differs so much in the length of its leg-bones 

 from the /'. inagnum of Cuvier, which it undoubtedly does if the 

 drawings and descriptions of both are correct ? and secondly, 

 how was it that Cuvier, with such a perfect skeleton as that in 

 the accompanying figure, should restore an animal with such 

 short and comparatively stout legs ? 



Someone perhaps may be able to throw some light upon these 

 points. W. Bruce-Cl.\rke 



The Telegraph in Storm-warnings 

 Tin; idea of using the electric telegraph to give warning of 

 cyclones approaching from a distance is generally supposed to 

 have first occurred to Prof. Hemyof the Smithsonian Institution 

 in 1S47 (Nature, vol. iv. p. 390). This however is not the 

 fact, for the same thing had been recommended in India |fully 

 five years before by the late Mr. Henry Piddington, in his sirth 

 "Memoir on the Law of Storms," published in the Journil of 

 the Asiatic Society of Bengal in 1S42. Referring to a storm which 

 was tracked from Macao to Shih-poo, and its estimated rate of 

 travelling, he says (p. 703): — "If China was a country under 

 European dominion, a telegraph might, when these storms 

 strike the eastern coast, warn those on the southern that they 

 were coming, and in India we might ofien attain the same advan- 

 tage. Oni- cliildrot may see this clone." In 1S49, when he pub- 

 lished the first edition of his "Sailor's Horn-Book for the Law 

 of Storms," he had not yet heard of the fulfilment in America of 

 his prophecy, which however he has duly noticed in subsequent 

 editions. Fred. Norgate 



Corydalis claviculata 



A SHORT additional note on Corydalis elavicnlala may be of 

 interest. A sprig placed in a glass of water and out of tlie way 

 of insects continues to grow and to bear flowers and fruit witli 

 nearly as much regularity as if still rooted to its native bank. 

 The flowers do not gape spontaneously; and, as most of the older 

 ones that I have examined in a state of nature have their lips 

 depressed, I think it certain evidence of the agency of insects, 

 though I have not yet been so fortunate as to witness their opera- 

 tions. All the flowers that I have seen are of a greeniih white, 

 but dried s]iecimens acquire the yellow tint described in syste- 

 matic works, a fail which may help to throw light on the some- 

 what parallel liehaviour oi Fnninria pallidiflora. 



Kilderry, C5. Donegal W. E. Hart 



POLARISATION OF LIGHT* 

 IX. 



THE results of combining two or more colours of the 

 spectrum have been studied by Helmholtz, Clerk 

 Maxwell, Lord Rayleigh, and others. And the com- 

 binations have been effected sometimes by causing two 

 spectra at right angles to one another to over'a ), and 

 sometimes by bringing images of various paits of a 

 spectrum simultaneously upon the retina. Latterly also 

 W. von Bezold has successfully applied the method of 

 binocular combination to the same problem [Pi'gL^fiufoiJ/', 

 Jubelband, p. 585}. Some effects, approximating more or 

 less to these, may be produced by chromatic polaris- 

 ation. 



ConipUmeiitaiy Colours. — First, as regards comple- 

 mentary colours. If we use a Nicol's prism N as po- 

 lariser, a plate of quartz O cut perpendicularly to the 

 axis, and a double-image prism P as analyser, we shall, 

 as is well known, obtain two images whose colours are 

 complementary. If we analyse these images with a prism, 

 we shall find when the quartz is of suitable thickness, that 



'^ \ : • Continued from vcl. i.\. p. 50S. 



each spectrum contains a dark band indicating the ex- 

 tinction of a certain narrow portion of its length. These 

 bands will simultaneously shift their position when the 

 Nicol N is turned round. Now, since the colours remain- 

 ing in each spectrum are complementary to those in the 

 other, and the portion of the spectrum extinguished in 

 each is complementary to that which remains, it follows 

 that the portion extinguished in one spectrum is comple- 

 mentary to that extinguished in the other. And in order 

 to determine what portion of the spectrum is complemen- 

 tary to the portion suppressed by a band in any position 

 we please, we have only to turn the Nicol N until the 

 band in one spectrum occupies the position in question, 

 and then to observe the position of the band in the other 

 spectrum. The combinations considered in former ex- 

 periments are those of simple colours ; the present com- 

 binations are those of mixed tints, viz. of the parts of the 

 spectrum suppressed in the bands. But the mixture 

 consists of a prevailing colour corresponding to the centre 

 of the band, together with a slight admixture of the spec- 

 tral colo.irs immediately adjacent to it on each side. 



The following results given by Helmholtz, may be 

 approximately verified : — 



Complementary Colours 



Red Green-blue 



Orange Cyanic blue 



Yellow Indigo-blue 



Yellow-green Violet 



When in one spectrum the band enters the green, in the 

 other a band will be seen on the outer margin of the red, 

 and a second at the opposite end of the violet ; showing 

 that to the green there does not correspond one comple- 

 mentary colour, but a mixture of violet and red, t'.e. a 

 reddish purple. 



Combinalioii of tivo Colours. — Next as to the com- 

 bination of two parts of the spectrum, or of the tints 

 which represent tihose parts. If, in addition to the appa- 

 ratus described above, we use a second quartz plate O, 

 and a second double-image prism Pj, we shall form four 

 images, say O O, O E, E O, E E. And if A, A' be the 

 complementary tints extinguished by the first com- 

 bination O P alone, and B, B' those extinguished by the 

 second Oj Pj alone, then it will be found that the following 

 pairs of tints are extinguished in the various images. 



Iinatie Tints extinguislied 



00 B, A 



O E B', A' 



E O B', A 



E E B, A' 



It is to be noticed that in the image O E the combina- 

 tion Qi Pi has extinguished the tint B' instead of B, because 

 the vibrations in the image E were perpendicular to those 

 in the image O formed by the combination Q P. A simi- 

 lar remark applies to the image E E. 



The total number of tints which can be produced by 

 this double combination O P, Qi Pi is as follows : — 

 4 single images 

 6 overlaps of two 

 4 overlaps of three 

 I overlap of four 



Total, 15 

 Collateral Co!iibiitatio?is. — The tints extinguished in 

 the overlap O O -|- E O will be B, A, B', A ; but since 

 B and B' arc complementary, their suppression will not 

 affect the resulting tint except as to intensity, and the 

 overlap will be effectively deprived of A alone ; in other 

 words, it will be of the same tint as the image O would 

 be if the combination Oi I'l were removed. Similarly 

 the overlap O E -|- E E will be deprived etTectually of A' 

 alone ; in other words, it will be of the same tint as E, if 

 Qi Pi were removed. If therefore the Nicol N be turned 

 round, these two overlaps will behave in respect of colour 

 exactly as did the images O and E when O P was alone 

 used. We may, in fact, form a table thus :— 



