136 



KNOWLEDGE 



[June 1, 1898. 



A somewhat norel departure in the work consists in the study of 

 vegetable physiology prior to a knowledge of the histology of plants ; 

 a plan which, we think, is open to criticism, inasmuch as it is fairly 

 comparable to entering upou the study of a steam engine before hariag 

 mastered the principles inToIved in the simple mechanical powers. 



The Suilding of the Intellect. By Douglas M. Ganc. (Elliot 

 Stock.) 58. The author of this book endeavours to present to the 

 reader some of the leading views pertaining to man's education in 

 all its aspects. He says : " Education being now regarded as a 

 question of such Tital importance, and opinions differing so widely 

 as to its method, character, and scope, a summary of the views of 

 tliose best qualified as guides and teachers cannot fail to arrive at 

 something like unanimity of ojjinion." The volume, which is happily 

 hung together, consists mainly of extracts from recognized authorities, 

 the author modestly preferring tliis method rather than the bolder 

 plan of clothing their opinions in his own words. 



We hnve received from Messrs. Darlington & Co., of Llangollen, a 

 parcel of their excellent handbooks for tourists, including their new 

 " Guide to London," by Mrs. E. T. Cook. This latter is probably the 

 most complete handbook to London ever issued. It is fully illustrated 

 with maps, plans, and views of the great city ; contains a most in- 

 forming index ; and is both well written and admirably planned. 

 Finally, Mr. E. T. Cook has himself contributed the chapters on the 

 British Museum, the National Gallery, and the National Portrait 

 Gallery. 



BOOKS RECEIVED. 



The Flora of Perthshire. By Francis Buchanan W. White. 

 (Blackwood.) 7s. 6d. net. 



The Cid Ballads. By the late .Tames Young Gibson. Edited by 

 Margaret Dunlop Gibson. (Kegan Paul.) Portrait. 12s. 



The First Philosophers of Greece. 'By Arthur Fairbanks. (Kegan 

 Paul.) 



The Epic of Sotnids. An Interpretation of Wagner's "Niebeluugen 

 Ring." New Edition. (Novello.) Illustrated. 3s. 6d. 



Flemeiitari/ General Science. By A. T. Simmons and L. M. Jones. 

 (Macmillan.) Illustrated. 3s. 6d. 



' First Stage Magnetism and Elect riciti/. ByR. H.Judc. (Clive.) 

 Illustrated. 2s. 



Heturn — Technical Education — Application of Fnnds hif Local 

 Authorities. (Spottiswoode.) Is. 6d. 



Text-Book of Physical Chemistry. By Clarence L. Speyers. 

 (Spou.) 



Electro-Physiology. By W. Biedermaun. Translated by Francis 

 A. Welby. Vol. II. (Macmillan.) Illustrated. 17s. net. 



The Story of Photography. By Alfred T. Story. (Newnes.) 

 Illustrated. Is. 



Responsible or Irresponsible ! Criminal or Mentally Diseased ! 

 By Henry Smith, m.d. (Watts & Co.) Is. 



Scientific Method in Bioloi/t/. By Dr. Ehzabetli Blackwell. 

 (Elliot Stock.) 



Industrial Electricity. Edited by A. G. Elliott. (Whittaker.) 

 Illustrated. 2s. 6d. 



The Process Year-Book for 1S98. (Penrose.) Illustrated. 



London in the Time of the Diamond Jubilee. By EmUy Constance 

 Cook. (Darlington & Co., Llangollen.) Illustrated. 



Urttevs. 



[The Editors do not hold themselves responsible for the opinions or 

 statements of correspondents.] 



" THE MASSES AND DISTANCES OF THE BINARY STARS." 

 To the Editors of Knowledge. 



Sirs, — Referring to Mr. Gore's paper on the " Masses 

 and Distances of the Binary Stars." In his paper of 

 December, 1894, he used — 25-5 as the stellar magnitude 

 of the sun. In his present paper he assumes —27, but 

 assigns no reason for the change. Will he explain 'r 



The word " brightness " seems to be used by Mr. Gore 

 in a sense in which I think it implies something he does 

 not intend. I may be wrong, but I think he means 

 "quantity of light." We cannot tell how "bright" 

 a star is when we only know its mass and distance. 

 We could if we knew its surface and distance. Assum- 

 ing that Mr. Gore is right in his data for y Leonis, for 



instance, and that its mass equals that of the sun, while it 

 emits two hundred and sixty-three times as much light 

 as the sun : this may be accounted for either on the 

 supposition that it is two hundred and sixty-three times 

 as bright, or a little over sixteen times the diameter of 

 the sun, or evidently any compensatory variations in the 

 two data. Of course Mr. Gore knows all this, but the 

 doubleuseof the word "brightness" gives trouble in reading 

 his papers, and leads him into such a sentence as, " Hence 

 we see that Sirius is nearly ten times brighter than it 

 would be had it . . . the same brightness of surface 

 as the sun has." It cannot be hri<jhter if of the same 

 brhjhtness. When I light a second candle I get twice 

 the surface and twice the light of the one, but neither 

 candle is brii/hter than the one first lighted. 



Edwin Holmes. 



To the Editors of Knowledge. 



Sirs, — Mr. C. B. Holmes's detection of Mercury on 

 April 12th, seven minutes after sunset, would certainly 

 establish " a record for a London view " if the object he 

 saw can be unquestionably identified as Mercury. The 

 planet Venus was, however, in the very same region of 

 sky, and not more than about six and a half degrees 

 distant, in a south-westerly direction, from Mercnry. If 

 Mr. Holmes really observed the latter, then he must 

 naturally have also seen the far more brilliant object 

 \'enus. 



Your correspondent's observation is such a remarkable 

 one that I am induced to suggest that Venus may possibly 

 have been mistaken for Mercury. On consulting my 

 note-books, I find that though I have obtained at least 

 ninety-four naked-eye observations of Mercury, I have 

 never been able, under the most favourable conditions, to 

 distinguish the planet within half an hour of sunset. 



Bristol, 1898, AprU 29th. W. F. Denning. 



"DESERTS AND THEIR INHABITANTS." 

 To the Editors of Knowledge. 



Sirs, — Mr. Lydekker, in your last issue (p. 101), ridicules 

 " the idea that flints and other stones grow." As one with 

 "more or less intimate acquaintanceship with science" 

 I think his illustration unfortunate and misleading, for if 

 segregation means growth — which I assume it does — then, 

 startling as it may appear, stones do " grow." 



G. Abbott, m.e.c.s. 



[Your correspondent fails to reahze the difference be- 

 tween rocl.s and stones. Rocks, during their formation, 

 such as the sand and shingle of our beaches, may, in a 

 sense, be said to gro^v ; but the stones composing such 

 shingle grow only in one way — that is, less. Similarly, 

 congretions and segregations, such as flints, grow while in 

 course of formation in their native rock, but, when denuded 

 and reduced to the condition of stones, only alter in size 

 by diminution. I must decline further discussion on the 

 matter. — R. L.] 



A LITTLE pamphlet giving " Local Particulars of the Total 

 Eclipse of the Sun on May 27th, 1900, ' has just been 

 issued from the XKUtical Almanm- office. In America, the 

 path of the moon's shadow reaches from New Orleans in 

 Louisiana to Norfolk in Virginia ; and in the Eastern 

 Hemisphere, from Oporto in Spain to Algiers in Northern 

 Africa. 



