December 26, 1907] 



NA TURE 



of nalurt;. To record an event according to nature- 

 histor)' is to fix its place in nature ; and to assist 

 the student in his record a series of sl-celeton classi- 

 ficatory schemes is provided. These tabular state- 

 ments contain many terms new to orthodox science, 

 and serve to illustrate the compiler's predilection for 

 classification. 

 Nietzsche in Outline and Aphorism. By A. R. Orage. 



Pp. viii+iSS. (Edinburgh and London: T. N. 



Foulis, 1907.) Price 2s. dd. net. 

 A^TER a short introduction dealing with Nietzsche's 

 works, a few pages of " definitions " and a sketch 

 of the philosophy formulated by the champion of 

 nihilism, the compiler brings together a series of his 

 author's aphorisms classified under such headings as 

 " Philosophers and Philosophy," " Morality," and so 

 on .As indicative of the searching character of the 

 maxims, one may be quoted from each of the sections 

 mentioned: — "The doer alone learneth"; "Educa- 

 tion ruins the exception for the sake of the rule." 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can be undertake 

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

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.] 



The Photoelectric Property of Selenium. 

 I HAVE lately coiibtiuctcd small seleno-aluminium bridges 

 for the electrical measurement of starlight, and it occurred 

 to me to put these bridges into a vacuum to see whether 

 their sensitiveness to light is thereby increased or 

 diminished. One of them, formed, of course, with con- 

 ducting selenium, had a resistance of 6ixio° ohms in air 

 and great sensitiveness to light. It was placed in a glass 

 tube connected with an air-pump. About twelve hours 

 after the tube was exhausted to a pressure of about o-oi 

 mm., the resistance of the bridge had dropped to 6i ohms! 

 From this it fell gradually, and it has now (three days 

 after exhaustion) a resistance of 17-5 ohms. 



I conclude, after repeating the result with three bridges, 

 that conducting selenium when placed in vacuo drops in 

 resistance about four million times, and possibly still 

 more. .Also it loses completely its sensitiveness to light. 



Other things connected with this strange result are under 

 investigation. I use the term "bridge," in preference to 

 " cell " or " resistance," at the suggestion of Dr. A. A. 

 Rambaut. These bridges are far more simple and easily 

 used with a telescope than the " cells " which I used in the 

 observatory of Dr. \V. E. Wilson in VVestmeath. The- 

 selenium employed was specially purified by Prof. Threl- 

 fall, who very kindly gave me a supply. 



George M. Mixcinx. 

 The Electrical Laboratory, O.xford, December 21. 



Early Chinese Description of the Leaf-Insects. 



" VuEN-KiEN-LUi-HAN'," a Chinese encyclopaedia completed 

 in 1703, torn, cdxlvi., fol. 9, b, has the following quotation 

 from the " Tau-hwang-tsah-luh," written c. ninth century: 



" In Nan-hai a peculiar manner of bees (or wasps) live 

 on the kan-lan tree iCanariiim pimela or C. album). They 

 look as if this tree's leaves were grown with hands and 

 legs, wherewith to grasp branches and so deftly adpress 

 themselves thereto that they are quite indistinguishable 

 from the foliage. Therefore, to collect them the southern 

 people used to fell the tree first and await the withering and 

 falling of its leaves : and only then they are enabled to 

 discern and gather the insects, which they employ as 

 philter." 



Nan-hai, literally " Southern Sea," was anciently the 

 appellation of a province, the present Kwang-tung. but 

 sometimes it was applied to the Indian Archipelago (Bret- 

 schneider. " Botanicon Sinicum," part iii., p. 579). 



But for specifying them as bees or wasps, this Chinese 

 account of the mimetic articulate would appear fairly to 

 tally with that of the leaf-insects fPhyllium). Probably it 

 is a very early, if not the earliest, description of these 

 Orthoptora. Kum.vgl'su Minak.wa. 



Tanabe, Kii, Japan, November 14. 



NO. 1 99 1, VOL. 77] 



w 



THE SALMON.' 

 E have no hesitation whatever in advising all 

 persons interested in the salmon, whether as 

 fishennen, naturalists, or legislators, to add this book 

 to their libraries. The blue and grey covers of the 

 official reports of the Scotch Fishery Board and the 

 Irish Department of .Agriculture contain a great deal 

 of most valuable information bearing upon the life 

 and habits of the salmon, and, so far as Scotland is 

 concerned, Mr. Caldervvood has now collected into the 

 book under- review the information spread over a 

 series of reports. In the case of Ireland the reports 

 of salmon-marking experiments are now published 

 separately in pamphlet form, and deserve a far wider 

 circulation than thev possess. 



Mr. Calderwood^ we think w'isely, confines his 

 book almost exclusively to the life-history of salmon 

 in Scotch waters, but is careful to direct attention to 

 points in which the habits of the saine fish in some 

 or all Irish rivers appear to diff'er in points of detail. 

 He would have us, in the first place, regard the 

 salmon as essentially a marine fish, and in this he 

 may be right, though we see no real reason why an 

 ana'dromous species need be definitely relegated to the 

 category of either fresh-water or marine foriiis. We 

 are, "however, quite in agreement with his view that 

 the' Salmonida are derived from originally marine 

 ancestors, and would even hazard the suggestion that 

 the presumably herring-like stock from which the 

 Salmonids and Alepocephalids are derived may have 

 been driven in the struggle for e.xistence either to 

 adopt an anadromous life or fresh-water habitat (as 

 in Osmerus, Salmo, Thymallus, and Coregonus), or 

 to retire into the deep sea like the Alepocephalids, 

 Argentina, Microstoma, and Bathylagus found off 

 our own coasts. 



We must, in any case, look upon the salinon as a 

 fish growing and feeding in the sea, resorting to 

 fresh waters when feeding ceases on the approach of 

 the spawning season, and spending the early part of 

 its life near the place of its birth until strong enough 

 to venture seawards; this is the standpoint from which 

 we must regard and seek to explain the known 

 phenomena of its life-history. 



It is now more than forty years since the discovery 

 was made that the first two' years of the salmon's life 

 are normally spent in the parr stage, while a few 

 parr may move seawards in the first year and a certain 

 proportion may spend three vears in fresh water. Mr. 

 Calderwood attributes this discovery to the Stormont- 

 field investigations, but we fancy he is so far in error 

 here that the percentages he quotes were really 

 derived from Dunbar's Thurso experiences, comrnuni- 

 cated by him to Archibald Young when Commissioner 

 of Scotch Salmon Fisheries. 



At a length (in the Tny) of five or six inches, the 

 parr assumes the silvery livery of tlie smolt, and 

 passes seawards, in Scotland, so far as observed, 

 always in spring. The second late summer or early 

 auturnn migration of smolts, noted annually in some 

 Irish rivers, and intermittently in others, has not yet 

 been observed in Scotland, and accordingly is not here 

 dealt with. 



On reaching the sea the smolt for a time eludes the 

 ken of man, or. at all events, all fishing gear 

 ordinarilv emplovcd bv him, until it reappears as a 

 grilse. This, hitherto 'little known, period of the fish's 

 history is admirably handled by Mr. Calderwood. The 

 few British and Irish records of young salmon between 

 the lengths of six inches and two feet are carefully 

 examined, and Dahl's Norwegian researches are cited 



I '• The Life of the S.-)Imon ; with Reference 

 in Scotland." By W. L. Calderwood. Pp. xxi 

 .\rnold, 1907.) Price 7^. 6t/. net. 



: especially to the Fish 

 b. (London : Edward 



