April 4, 1895] 



NATURE 



54: 



M' 



SCIENCE IN THE MAGAZINES. 

 R. CHAS. DIXON has discovered a new law of geo- 

 graphical dispersal of species, and he expounds ils cap- 

 abilities in the Fortnighlly. Here is a statement of his con- 

 clusions : — "Species in the northern hemisphere never increase 

 their range in a southern direction; they may do so north, north- 

 east, or north-west, east or west. Species in the southern hemi- 

 sphere never increase their range in a northern direction ; they 

 may do so south, south-east, or south-west, east or west. The 

 tendency of life is to spread in the direction of the poles. 

 Among the six corollaries which I have drawn from this law, 

 mention may be made of the following. By the fourth corollary, 

 species never retreat from adverse conditions. If overtaken by 

 such they perish, or such portion of the species that may be ex- 

 posed to them. I5y the fifth corollary, extension of range is 

 only undertaken to increase breeding area. By the sixth 

 corollary, contraction of range is only produced by extermin- 

 ation among sedentary species, and probably also by extermin- 

 ation (through inability to rear oflTspring) among migratory 

 species that are neither inter-polar nor inter-hemisphere. . . . 

 If this law of geographical distribution be true, polar 

 dispersal of species — in other words, from the direction 

 of the poles towards the equator — is a myth." Mr. 

 Dixon brings forward a number of facts in support of his 

 theory, which will no doubt be given the consideration it 

 deserves. 



An address by Mr. Leslie Stephen, on the choice o'' books, 

 appears in the National ; but, to prevent misconception, it is 

 just as well to state at once that scientific literature is altogether 

 ignored. Yet it is difficult to understand why this should be, 

 for writings of men of science are apparently included in the 

 definition stated by Mr. Stephen himself. " Literature, in short," 

 he writes, "is one utterance of Matthew .Arnold's Zeitgeist 

 — the v,-»gue but real entity which is a summary of all the sym- 

 pathies and modes of thought and feeling characteristic of the 

 best minds at a given stage of human progress." A few natural 

 history notes will be found in the .\'a!ioiial, in an account, by 

 Miss Balfour, of a journey through the British South Africa 

 Company's territory, in 1894. 



Among other popular articles on natural history in the maga- 

 zines received by us, we notice " Nestlings," by the Rev. 

 Theodore Wood, in the Sunday Magazine, and " Snake- 

 Taming" in Chambers' s yournal. This periodical also con- 

 tains a very readable elementary description of the great Indian 

 Trigonometrical Survey. Mr. L. N. Badenoch describes a 

 ! number of species of Plasmidse in Good Words. In the same 

 magazine Sir Robert Ball writes on (he life and works of Coper- 

 nicus. Under the title, "Tesla's Oscillator and other Inventions," 

 a good account of some of Mr. Tesla's recent electrical work is 

 given in the Century, by Mr. T. C. Martin. The article "dis- 

 closes a few of the more important results he has attained, some 

 of the methods and apparatus which he employs, and one or 

 two of the theories to which he resorts for an explanation of 

 what is accomplished." It is illustrated with fifteen figures, 

 all of which possess points of interest. Mention must be made 

 here of a short biographical sketch of Helmholtz, contributed by 

 Mr. Martin to the Slarch number of the Century, but overlooked 

 at the time. The sketch is illustrated bv a fine engraving from 

 a photograph of Helmhollz, taken in 1893. A brief note in 

 CasseU's Family Magazine describes some curious tubular 

 dwellings constructed against the side of a small aquarium by 

 the species Ampliitho: litlorina. The tubes are semicircular, 

 and composed of sand and small pieces of seaweed, ce- 

 mented together with a glutinous mailer secreted by these 

 shrimps. 



The practicability of constructing a railway from the Mediter- 

 ranean to India is discussed by Mr. C. E. D. BK-ick in the 

 Contempcra)y. Over India proper there are 18,500 miles of 

 lines open to traffic. But westward these lines break off at 

 Peshawur, Chaman, and Kurrachee. It is proposed that a line 

 should be constructed from Port Said, through Northern Arabia, 

 along the edge of the Persian Gulf, to Kurrachee— a di»tance 

 estimated at 2400 miles. 



In addition to the magazines mentioned in the foregoing, the 

 Humanitarian, Scribner, and Longman's Magazine have 

 been received. A portrait of Prof. Bonpey accompanies 

 an article on " Science and Faith " in the first of these 

 magazines. 



NO. 1327, VOL. 51] 



PRECIOUS STONES, AND HO IV 

 DISTINGUISH THEM.^ 



TO 



A MONG the duties which fall to the lot of an official in the 

 •^~*- Mineral Department of the British Museum, in his other- 

 wise unromantic and sternly studious life, is one which is not 

 altogether devoid of human interest. It may happen, for 

 ' example, that a lady having inherited a priceless heirloom in 

 i the shape of a large emerald, travels from the Antipodes in 

 order to sell it in England for its true value, and desiring to 

 display its charms brings it to the Museum. To inform such a 

 person that the stone is but green bottle glass cannot be a 

 pleasant task. 



Only within the last few months came an Afghan prince 

 who had sold his worldly goods, travelled to the coast of India, 

 and worked his passage to England, having secreted about his 

 person a stone which he supposed to be of enormous value. 

 His story was that as he slept upon the hillside, Mahomet had 

 appeared to him and told him that he would find a rare jewel 

 under his hand. The poor man could not be convinced that a 

 stone with this celestial guarantee could be anything common; 

 for, as he said, "Mahomet cannot lie." Be this as it may, 

 the stone was quartz, and its princely owner could only be 

 advised to repair his fallen fortunes in some Oriental fashion at 

 Constantinople — Kensington. 



It is curious that the stones brought by such people are always, 

 in the opinion of their owners, gems of the greatest value and 

 rarity. Could they but have consulted some competent expert 

 nearer home, they would have been saved time and money and 

 bitter disappointment. 



But after such interviews, I have always been very forcibly 

 impressed by the fact that even the experts do not seem in the 

 least aware of the simple and certain methods which have been 

 placed at their disposal by recent mineralogical research. There 

 is, perhaps, no subject in which experts have been so slow to 

 I take advantage of practical methods supplied by science as in the 

 manipulation and discrimination of precious stones. 



The stones brought by these chance visitors have often been 

 bought and sold over and over again under totally false names. 

 \ There is, I suspect, scarcely a collection, public or private, in 

 which some of the jewels are not wrongly described. 



Mistakes are constantly made ; and these are sometimes of 

 considerable commercial importance. It may be remembered, 

 for example, that a few years ago much excitement was caused 

 by the discovery of rubies in the Macdonell Range in Southern 

 Australia. Much time and money was wasted in their extrac- 

 tion before it was discovered that, like the so-called Cape rubies, 

 they were merely garnets. 



I should be the last person to underrate the great value of 

 that knowledge which results from long experience, or to deny 

 that in ninety-nine cases out of a hundred an expert may be 

 absolutely right. Every one must admire the confidence with 

 which a practised eye can even pick out from several packets of 

 diamonds those which came from a certain mine. 



Such a professional expert may in five seconds pronounce a 

 judgment which it might require half an hour to establish by 

 scientific methods, and one which may be equally correct. 



But there is a vast difi'erencc between "maybe" and "is," 

 and scientific men are not satisfied with that sort of judgment, 

 but require actual proof. 



One ought to distinguish between two sorts of expert know- 

 ledge — that which results from long experience and the training 

 of eye and hand, and that which results from familiarity with 

 , scientific methods. To have confidence in the non-scientific 

 expert, one must place reliance upon his personal character and 

 the soundness of his senses, and be sure that liis .actual ex- 

 perience has included problems similar to the one submitted to 

 him, and even then he may fail in that hundredth case. 



But the scientific tests cannot err ; moreover, they furnish 

 \ a proof which carries conviction to .all who see it. The opinion 

 of the expert need convince none but himself. 



An exact parallel is lo be found in medical practice. It is 

 no doubt often possible for a doctor of experience to diagnose 

 diphtheria and phthisis by their symptoms. But in recent years 

 new methods have been made available by the discoveries 

 relating to bacteria, and at the present time no diagnosis of 

 diphtheria or of the early stages of consumption would be con- 



* A lecture delivered at the Imperi.il Institute, by Mr. H. A. Micrs. 



