198 



NATURE 



[October 22, 1914 



expression, we find that they are respectively + 0016 

 and +0022, so that the theoretical value of fe becomes 

 6451 + 0038, that is, 0489. This even is in worse 

 agreement with the experimental value 0434 than the 

 value 0-451 usually given, but a consideration of the 

 experimental conditions shows that the value to be 

 deduced is in reality 0-492, which is in excellent agree- 

 ment. The argument will shortly be published in 

 full. E. Cunningham. 



St. John's College, Cambridge, October 14. 



Flint Fracture. 



It is to be regretted that the letter of Mr. Reid 

 Moir in Nature of September 24 has received no 

 reply. If chemists, mineralogists, petrologists, and 

 physicists could have been made to realise the fruitful 

 fields for profitable and far-reaching research opened 

 to them by this subject, our knowledge would be in 

 a very different state to-day, and many of the con- 

 tentions and mysteries would be replaced by demon- 

 strable facts. 



In all text-books we see descriptions, or references, 

 to lydite, the touchstone of the goldsmith, and in 

 museums and collections we see specimens bearing 

 this name; all kinds of origins are claimed for it; 

 sedimentary, volcanic, metamorphic, and one has even 

 seen meteoric. In text-books we see descriptions of 

 the pebbles in the Blackheath beds ; we are told they 

 are pebbles of flint still retaining their original black 

 colour. As a matter of fact, they are not black flint; 

 they are now of various colours. It is their surface 

 that is black; the metamorphosed portion may not be 

 thicker than tissue paper, but other examples can be 

 found upon a sea-beach where it is an eighth of an 

 inch thick, and from this onward until the whole is 

 metamorphosed, and we have the jet-black mineral, 

 which does duty under the name of lydite ! 



Just one more example. The same text-books de- 

 scribe the beautiful " Egyptian jasper " ; some say the 

 locality from which this has been derived is unknown ; 

 others venture to suggest one. One of the many 

 metamorphoses of flint is jasperisation. We see this 

 commence on the surface of flints (one of the things 

 called patination); this proceeds in intensity and 

 centrewards until the whole substance is altered, and 

 we have the rich mottlings of yellows and browns, 

 quite equal to those of Egypt. The so-called Egyptian 

 jasper may be a metamorphosed British flint." 



Mr. Reid Moir refers to lines radiating from the 

 point of percussion on the fractured face of a flint; 

 here is something for the physicist; they certainly 

 are not "fissures," but rather lines of force (closely 

 connected with facetted cones and stellate fracture). 

 The best place to see these, and study them, is in 

 asphalt or pitch. So long as the "fracture-" or 

 " flaking-plane " maintains itself constant, i.e. in 

 relation to the striking-plane, they remain fairly 

 simple. If, however, the fracture-plane resolves, or 

 even undulates very deeply, then a very remarkable 

 phenomenon obtains, and the lines end in a row of 

 cones^ just over the escarpment, looking like a row 

 of pointed tents with a rope passing from the centre 

 pole of each to the point of percussion ! 



The last weeks of Sir John Evans, before he took 

 to his final bed, were spent In studying a large collec- 

 tion brought together to put the whole subject of 

 llthoclasiology on a scientific footing. His last words 

 to the collector were : " Promise me that If I do not 

 pull through this operation, you will lose no time in 

 publishing all this. I am certain that this is where 

 we ought to have started sixty years ago, and no real 

 progress will be made until we start here." 



NO. 2347, VOL. 94] 



If we take half a dozen pieces of flint of exactly 

 the same shape and size, and apply exactly the same 

 force, administered in exactly the same manner, and 

 of exactly the same intensity, the results may be very 

 different in each case. Before we can argue from the 

 effect to the cause, we must know something about 

 the nature of the object acted upon. We must start 

 with the origin and nature and varieties of silica, 

 the various metamorphoses and molecular rearrang- 

 ing to which each variety is subject, and how each 

 variety, in each state, responds to dj'namic agency, 

 whether administered by nature or man. 



So also when we come to dynamics we must study 

 every mechanical possibility, single them out, and 

 name them, so that every observer may know what 

 the other is speaking about. There must Ije no 

 "peculiarities known only to the student," and "no 

 features known only to myself." Each phenomenon 

 must be capable of separate study, and receive a 

 special name, so that all understand what they are 

 talking about. 



There are few who appreciate the splendid work 

 which Mr. Reid Moir has been doing more than 

 myself, but I am quite sure that if he were to restart 

 the subject, on the lines here indicated, in a very 

 short time he would regard the points he raises with 

 very different eyes. W. J. Lewis Abbott. 



8 Grand Parade, St. Leonards-on-Sea. 



Filtering Power of Sand. 



The letter of Mr. C. J. Watson in Nature for 

 October 15, recommending that " Nachtblau " (night- 

 blue) should be used for experiments on adsorption by 

 sand, leads us to point out that so far back as 1909 

 we demonstrated before the International Congress of 

 Applied Chemistry (Section IV. B, p. 7) the striking 

 experiment in which a solution of this dye issues 

 perfectly colourless after passing through a column 

 of purified sand. Since this date the experiment has 

 been frequently used for demonstration purposes at 

 lectures on adsorption by ourselves and others. 



We showed In 1909 the remarkable quantitative rela- 

 tions existing between the weight of sand and the 

 weight of dye absorbed ; each degree of fineness of 

 the sand is characterised by a remarkably sharp co- 



„ . , , . , , weight of dve adsorbed 



efficient of adsorption, the value . . ^ ' .. t — 



^ weight of sand 



being constant for the same sand to the sixth decimal 

 place (In one series, for example, values 0000147 to 

 0000148 being obtained). The relation of these experi- 

 ments to the general theory of dyeing was dealt with 

 in the paper cited, and also in a later communication 

 to the Society of Chemical Industry (1912, vol. xxxi.). 



W. P. Dreaper. 



W. A. Davis. 



Scientific Societies and the War. 



Suggestions have recently been made that certain 

 of our scientific societies should suspend their meetings 

 for the present, on the ground that "it is difficult to 

 take an interest in such things just now." To those 

 who share this feeling, it may be worth while to point 

 out that, as already recorded in Nature, the Academic 

 des Sciences held its usual meeting Paris on Septem- | 

 ber 7. Under that very date, in the Times review of 

 the war for September, we find the entry, " Germans 1 

 reach the extreme point of their advance." Among . 

 our gallant Allies, at all events, " le tour d'lvoire ne i 

 se rend pas." W. T. Calman. j 



British Museum (Natural History), October 16. 



