412 



NA TURE 



[March 3, 1898 



we cannot but regret the absence of any attempt to 

 formulate a theory of them. The work is divided into 

 three parts ; in the first the effects of white hght are 

 studied, in the second the different parts of the spectrum 

 are taken separately, and the third contains experiments 

 on the increase of sensibility due to colouring matters. 

 Flates of copper coated thinly with oxide, sulphide, 

 fluoride, bromide and iodide, of tin coated with oxide 

 and sulphide, and of silver coated with sulphide, are 

 examined in solutions of some thirteen different salts. • 



The electromotive force developed depends on many 

 circumstances, such as the thickness and nature of the 

 coating, the concentration and nature of the electrolyte 

 and the temperature, so that it is difficult to prepare two 

 identical cells. The electromotive force of a given cell 

 is, however, proportional to the intensity of the light 

 when this is not too large. All the elements had a 

 maximum sensibility in some part of the spectrum, the 

 position of the maximum depending on the nature of the 

 coating on the plates, but, for a given instrument, being 

 independent of the nature of the electrolyte. With dyed 

 plates the position of the maximum was independent of 

 the compound of copper employed, but was determined 

 by the nature of the dye, and was always found at a 

 wave-length greater than that for which the colouring 

 matter had a maximum absorption. The sensibility is 

 largely increased by the employment of colouring matters. 

 The actinometers may be employed for photometric 

 purposes, since* it is possible to prepare one with a 

 maximum sensibility for almost any wave-length. Since 

 the development of the electromotive force is accurately 

 synchronous with the action of the light, they may also 

 be used as radiophones. 



Neudruckc von Schrifien und Karten iibcr Mcteor- 

 ologie und Erdmagnetisnius. Edited by Prof. Dr. 

 G. Hellmann. No. lo, Rara Magnetica, 1269-1599; 

 No. II, Ueber Luftelektricitat, 1746-1753. (Berlin: 

 A. Asher and Co , 1898.) 



Dr. Hellmann is so well known by his laborious 

 researches in matters relating to the history of early 

 scientific documents and instruments, and by the very 

 valuable bibliographical knowledge which he brings to 

 bear upon the various publications of this nature, that it 

 is unnecessary to say more than that the present volumes 

 exhibit the same painstaking labour as those which have 

 preceded them. The first contains fac-simile copies of - 

 some of the earliest papers on terrestrial magnetism and j 

 the mariner's compass ; each document is very scarce, 

 and only accessible with difficulty, and must be con- 

 sidered as a literary rarity. Among them is a letter from 

 Pierre do Maricourt, dated August 12, 1269, which is the 

 earliest known treatise on magnetism in Europe. The 

 principal point in the paper is the distinction of the two 

 poles of the magnet, and of their opposite attraction. A 

 paper by F. Falero (Sevilla, 1535) contains the first 

 published instructions for determining the magnetic 

 declination, although its existence was discovered by 

 Columbus in 1492. A letter by G. Hartmann, dated 

 March 4, 1544, gives an account of his discovery of 

 the magnetic dip and the first determination of the 

 declination on the mainland. This document was buried 

 in the archives at Konigsberg until 1831, so that the 

 discovery of the magnetic dip is generally attributed to 

 R. Norman, who determined it for London in 1576. In 

 a letter from G. Mercator to the Bishop of Arras, which 

 was discovered during the present century in the library 

 at Gottingen, the first mention is made of the earth pos- 

 sessing a magnetic pole. There are various other papers 

 which we cannot refer to here, all of which are of great 

 interest and value in throwing light upon the earliest 

 development of the subject. The second volume con- 

 tains a reproduction of the first fundamental papers 

 relating to atmospheric electricity. The electrical nature 



NO. 1479, VOL. 57] 



of thunderstorms was suspected early in the eighteenth 

 century by Hauksbee and other Englishmen, but Prof. 

 J. H. Winkler, of Leipzig, first clearly demonstrated the 

 analogy between them and the electric spark in 1746; 

 the experimental proof was proposed by B. Franklin in 

 1749, and first carried out, near Paris, by Dalibard on 

 May 10, 1752. 



LETTERS TO THE EDITOR 



The Edt'/or does vol hold himself responsible for opinions ex- 

 pressed hy his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of rejecteit 

 niamiscripfs intended for this or any other part of NATURE. 

 No notice is taken of anonymous communications.'] 



Does a Phosphorescent South American Liana exist.' 



In collecling the literature regarding phosphorescent plants, I 

 ; chanced on an article, by Mr. C. F. Holder, on "Living Lamps," 

 i in No. 392, vol. Ixvi. (]scn\xa.xy \'i?>2,) oi Harper^ s AJagazine. In 

 i this article, at page 191, it is said : " In South America, a vine 

 I known as the Cipo, when injured, seems to bleed streams of 



living fire. Large animals have been noticed standing among its 



crushed and broken tendrils, dripping with the gleaming fluid, 

 ' and surrounded by a seeming network of fire." 

 ■ Could any reader of Nature confirm the existence of this 

 ! Cipo with a phosphorescent sap? Cipo, I believe, is a name for 

 j liana, not for vines. If true, the existence of a phosphorescent 



sap in a superior plant would be of great physiological interest. 

 ! But no mention of this or a similar case is to be found in the 

 ' standard works on vegetable physiology. I fear the statement 



may have as much foundation as the assertion, made in the 

 I same article, that among the peasantry of Italy girls complete 

 , their gala toilet with diadems of fireflies. Italo Giglioli. 

 , Portici, near Naples, February 18. 



I Insusceptibility of Insects to Poisons. 



i Your reviewer's observation that one insect's food is another 

 ' insect's poison, is applicable to a single insect at different stages 

 of development. The scarlet fungus, Agartcus muscarius, 

 derived its name from use in an old-fashioned decoction for fly- 

 papers ; nevertheless, it is eaten freely by maggots. Other 

 poisonous fungi, such as A. icruginosus, A. phalloides, Riissula 

 emettca, &c. , are evidently innoxious to maggots and slugs. 

 With regard to the effect upon more highly organised animals, 

 it may be noted that Boletus lurtdus is eaten by mice and rabbits, 

 and that squirrels are very partial to several species of Tricholoma 

 and Boletus. I have some doubt as to whether .squirrels are not 

 occasionally poisoned by eating fungi, but I have not noticed 

 any suspicious mortality in the case of the rabbits or mice. 

 February 19. H. B. Potter. 



The Mandrake. 



I.N" a foot-note to my letter under this heading (Nature, vol. 

 liv. p. 343, August 13, 1896), I quoted from a Chinese work the 

 names of the nine plants reputed to assume frequently the human 

 or animal figures ; and I remarked thereon that most of the 

 alleged figures in these plants were recognised in their subter- 

 raneous members. Irately, however, I have found this remark 

 not quite correct, inasmuch as it concerns some of them, viz. 

 mustard and turnip : the alleged figures in these two appear to 

 have suggested themselves to the Chinese imagination by the 

 deformities in their floral parts caused by some parasitic infest- 

 ations. This is evident from the lollowing passage that occurs 

 in " Mung-ki-pih-tan," written by Chin Kwoh (1031-94 a.d.) : 

 " When such vegetables as the turnips and mustard are injured 

 by draught, their inflorescences mostly form the blossoms re- 

 sembling the lotus-flower, or like the dragon and serpent. These 

 are of common occurrence, and anything but wonderful. Once 

 in the period of Hi-ning (1068-77 a.d.), when Mr, Li Kih-chi 

 was the governor of Jun-chau, all blossoms of the vegetables in 

 his garden happened to have the form of the lotus-flower, each 

 having one Buddha sitting in it. They were innumerable, and 

 looked as if engraved, and well preserved the figures after desic- 

 cation. Some one used to ascribe this ominous event to the 

 great zeal with which all members of Mr. Li's family devoted 

 themselves to the worship of Buddha." 



February 21. KuMAGUSU Minakata. 



