December 29, 1892] 



NATURE 



199 



are the sins that do so easily beset writers on popular 

 science. The volume, which contains some excellent 

 illustrations, deals with "pioneer labourers," "soil- 

 makers," "soil-carriers," "soil-binders," "field- 

 labourers," "guests welcome and unwelcome," 

 " nature's militia," and so forth. We do not propose 

 to tell who or what the labourers, the guests, or the 

 militia are. We advise those of our readers who are 

 interested in the transactions of the Great World's Farm 

 to get the volume and ascertain for themselves. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

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

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.^ 



Measurement of Distances of Binary Stars. 



Some years ago I communicated to a few astronomers a plan 

 for measuring the distance which separates us from some of the 

 binary stars, i)elieving, as I did, that by using the diameters of 

 their paths as a basis, determinations of distance could be made 

 which are impossible with the means at present in use. 



This basis could, I hoped, be calculated by first ascertaining 

 the velocities with which the stars are moving in their paths, in 

 a somewhat similar manner to that employed for measuring the 

 motions of stars with the spectroscope, except that instead of 

 making a comparison with a hydrogen flame, the spectra of the 

 two star- should be compared by photographing them together. 

 The width of any double lines, which may show themselves 

 (the one line belonging to the spectrum of the receding star, and 

 the other to the advancing one) would be a measure of their 

 velocities expressed in miles. Applying this information to the 

 known period of revolution of the system, iis diameter can also 

 be expressed in miles, and this would enable one to estimate 

 the distance from the earth if the angle betvteen the two stars 

 were known. This sugnestion has already borne fruit, the 

 relative velocity of some rapid, but as yet inseparable, binaries 

 having recently been determined. 



The answers received to my suggestions were discouraging, 

 but since then instruments have been improved, and I trust that 

 you will think the matter of sufficient importance to be brought 

 before the notice of your numerous astronomical readers, ^^hould 

 any of them be able to make the necessary determination, a 

 foundation-stone will have been laid, not only for obtaining a 

 true idea of perhaps undreamt of stellar distances, but also of 

 the masses of bmary stars, and possibly a connrction may 

 ultimately be traced between them and the adjoining ones. 



The two most brilliant binaiy stars are a Centauri and 

 ■a Geniinorum, and as in both these cases the paths are elon- 

 gated ellipses, and the stars near their extremities, efforts should 

 be directed towards determining their distances as suggested 

 above. C. E. Stromever. 



Strawberry Hill, November l6. 



Remarkable Weapons of Defence. 



The following extract from a letter from such a careful 

 bserver as Mr. E. E. Green is of such general and special 

 interest as to require publication. 



Mr. R. J. Piicock informs me that the Acaroid is almost 

 <;ertainly Jlolothyms coccinella, Gerv., a species that appears to 

 be common in Mauritius, and that in the lateral membranous 

 area between the carapace and the cephalothoracic limbs is a 

 ditinct orifice which was regarded by Dr. Thorell as of respira- 

 tory import, but in connection with Mr. Green's interesting 

 discovery of the existence of offensive glands in this animal it 

 is necessary to bear in mind the possibility of its being the 

 outlet of the e organs. 



The mite has such a hard integument, that being taken into 

 the mouths of the lizards and birds that would probably prey 

 upon it in the situations it frequents, would probably do it little or 

 no damage if it were speedily rejected. G. F. Hampson, 



The accompanying insects — apparently Orobatid mites — 

 were found by me in the district of Tallawakelle, Ceylon (alt. 



NO. 1209, VOL 47] 



4600 ft.), under stones and rocks in damp, shady situations. It 

 was only by accident that I became aware of their remarkable 

 weapons of defence — an exceedingly pungent secretion. 



About five hours after handling one of these insects I accident- 

 ally touched my tongue with my finger. Immediately an extra- 

 ordinarily pungent, galvanic sensation or taste commenced rapidly 

 to spread over my mouth, quickly reaching my throat. Rinsing 

 my mouth and gargling with hot water failed to arrest the progress 

 of the sensatii>n., which was accompanied with exce.-sive saliva- 

 tion. The unpleasantness lasted for several hours, and then died 

 away without any further consequences. I also unconsciously 

 rubbed my face, at the angle of the eye, with the same finger ; 

 after which a rather pleasant warmth spread over that part of 

 my face, and was distinctly perceptible the foil > wing morning. 



I could not for some time trace the cause of this effect. I 

 at first put it down to the agency of a fungus that 1 had been 

 carrying, but a further experiment negatived this idea. I 

 afterwards tested the insect, and found it to be the real agent. 

 The experiment was repeated at my suggestion, by a medical 

 friend — Dr. R. J. Drummond— who can testify to the result. 

 He described the sensation as somewhat like that produced by 

 the strongest menthol. We both noticed that it had a numbing 

 effect upon the mucous membrane of the mouth. 



It is evident that ihis property must be a very efficient protec- 

 tion to the insect. The rapidity with which the secretion acts 

 would cause it to be very quickly ejected if picked up by either 

 a bird or a lizard — the only enemies that would be likely to 

 attack it. E. Ernest Green. 



Eton, Pundulorja, November. 



A Suggestion. 



As very shortly now Nature will reach its jubilee volume, 

 I hope you will permit me, as an uninterrupted subscriber 

 for nearly twenty years, to offer a suggestion with regard to that 

 occasion. 



As the volumes of Nature contain original contributions, 

 observations, and notes in all branches of science, more varied 

 and valuable than are to be found in any other scientific periodi- 

 cal publication in existence, there is not a worker, in whatever 

 branch he may be engaged, that does not find it necessary to be 

 continually referring to its pages ; but, unfortunately, through 

 lack of a general handy index, he discovers what he wants only 

 after the expenditure of a very great deal «>f time and worry. 



I write, therefore, not only in my own name, but (by request 

 in a private way) in that of a large number of fellow-workers in 

 the sub'ects in which I am myself specially interested — biology, 

 palaeontology, anthropology, geography — to suggest that you 

 should celebrate the jubilee of Nature by conferring on your 

 readers the immense boon of a classified index t) its contents. 



During some investigations I was making in 1876-7 I so felt 

 the need of a collected index that I went to the trouble of com- 

 piling for myself one, up to that date, classified according to 

 sciences, subdivided again according to the sections of each, 

 which in subsequent work saved me weeks of time and trouble. 

 To my regret, this MS. got lost or destroyed, and there is 

 nothing in connection with Nature that I, and I am certain 

 every other worker, would now hail with greater satisfaction 

 than the announcement that the means of reaching whh expe- 

 dition and precision the treasures at present so deeply buried in 

 your (nearly) fifty priceless volumes, will be ced within our 

 reach with its jubilee volume. Old Subscriber. 



Superstitions of the Shuswaps of British Columbia. 

 Referring to the above, as recorded by Dr. George Dawson, 

 F. R.S., ill the Transactions of the Royal Society of Canada, and 

 included in your Notes of last issue, in which attention is called 

 to the belief among the Shuswaps and some other North 

 American races, that small lizards enter the bodies of men, 

 pursuing them, and devouring their hearts, I was at once 

 struck with the almost exact resemblance of this belief to one 

 very generally prevailing in Ireland, as regards common water 

 Newts, which go by the name of Man-eaters (pronounced Man- 

 aters). This I can testify to from personal knowledge ; but it 

 has been accidentally confirmed by an experiment which I hope 

 I may be pardoned lor referring to. Where I reside are three 

 Irish servants, to whom I caused to be shown a dia>«ing of the 

 Water Newt, and with the request that I might be told its 



