424 



NATURE 



[June 26, 1913 



be bordered by escarpments of simple pattern ; the 

 escarpments will gradually be dissected by ravines and 

 valleys, but these cannot be eroded beneath sea-level ; 

 hence the arm of the sea that takes possession of 

 such a trough cannot have lateral branches or indenta- 

 tions, unless the sides of the trough as well as the 

 trough block itself suffer depression — that is, unless 

 regional depression takes place. Likewise, a coastal 

 valley may be occupied and over-deepened by a glacier, 

 and invaded by the sea after the glacier withdraws, 

 thus producing a fiord ; but a fiord can be easily 

 distinguished from a drowned fault trough or from a 

 ria. Evidently, then, in applying Dana's proof, it is 

 essential to see that glacial fiords and fault troughs 

 are not confused with normal valleys ; and it still 

 appears to me that my article of February 6 made it 

 clear that only normal valleys were under considera- 

 tion. 



A few words as to terminology. Various popular terms, 

 like "fish" and "valley," which entered our language 

 in a pre-scientific period, have to-day two meanings; 

 first, their original general meaning, and second, a 

 later acquired and more precisely limited scientific 

 meaning. " Fish " originally meant an animal living 

 in the sea, and included whales and oysters. The latter 

 are still known as shellfish, and a certain kind of 

 whale is still named blackfish ; but under the influence 

 of scientific zoology whales are now classed by most 

 persons not with fish but with mammals. So with 

 " valley " ; the original meaning of the word is simply 

 an enclosed lowland, more or less elongated, of what- 

 ever origin, and this vague meaning is still in common 

 use, as in naming the valley of the Wye, purely the 

 work of normal erosion ; the valley of the Ticino, 

 greatly modified by glacial erosion ; the valley of the 

 middle Rhine, a fine example of a down- 

 faulted trough ; and the valley of California, 

 a broad and relatively shallow down-warp. 

 But "valley" has also been used, since the time 

 of Hutton and Playfair, in the scientifically limited 

 sense for forms of normal erosion under the action 

 of rain and rivers ; and when thus used it implies an 

 origin above sea-level, as well as the systematic 

 arrangement of certain significant features, such as 

 slope of stream line, manner of junction of tributary 

 and main valleys, and so on, by which the normal origin 

 of a valley may be easily recognised. The Norwegian 

 term "fiord" (fjord), and the Spanish term "ria," 

 both locally used without scientific definition or impli- 

 cation of origin for the sea-arms that they designate, 

 have in recent vears both been given a more limited 

 meaning in scientific geographical literature. It was 

 only, as the context shows, in the scientific sense of 

 a form of normal erosional origin above sea-level that 

 the term "valley" was used in my article; and mani- 

 festly it is onlv to coasts which exhibit branching or 

 indented embavments, such as were shown in the 

 middle block of my diagram, and such as are caused 

 bv the submergence of true valleys of erosion, that 

 Dana's proof of Darwin's theory applies. 



W. M. Davis. 

 Harvard University, Cambridge, Mass., June 7. 



Uniformity in Radio-active Nomenclature. 



In a letter to Nature of June 5, Mr. W. H. Ross 

 and Mr. H. J. Creighton point out the present want 

 of uniformity in radio-active nomenclature, and sug- 

 gest that some definite system should be adopted by 

 all writers on this subject. Every worker in radio- 

 activitv recognises the importance of some agree- 

 ment in regard to this matter. It is difficult, how- 

 ever, for a single individual to suggest a scheme 

 which would be likely to gain universal support. The 

 only international body existing at present which is 

 in a position to deal with such a question conveniently 

 NO. 2278, VOL. 91] 



and expeditiously is the International Radium 

 Standards Committee. The constitution of this com- 

 mittee is fortunately very suitable for the considera- 

 tion of this question, as it comprises about an equal 

 number of physicists and chemists representing five 

 nations. As president of the International Committee, 

 I should be glad to bring the matter to the attention 

 of the other members, and will do so if there is no 

 objection to this proposal. E. Rutherford. 



Radio-activity and the Age of the Earth. 



Mr. Holmes, in his interesting letter in Nature of 

 June 19, brings out the embarrassments in which the 

 superabundance of radio-activity in the. accessible 

 crust of the earth and the enormous antiquities deduc- 

 ible therefrom have plunged physics. His explanation 

 is that since the earth as a whole cannot be as radio- 

 active as the crust, without liquefying, there cannot 

 be as much radium in it as might be inferred from 

 the samples we can take, and that its " heavy- 

 metallic core" must be "completely destitute _ of 

 radium." This, however, involves the improbability 

 that the heaviest metal of all, uranium, has not gravi- 

 tated to the "metallic core," and does not explain 

 why this core should be destitute of radio-active 

 substances. 



It may be pointed out, therefore, that the whole 

 reasoning rests on an assumption to which alterna- 

 tives might be considered. It is assumed that the 

 dissociation of uranium has been proceeding always 

 and everywhere at the rate we can now observe on 

 the earth's surface. But it is possible that under the 

 physical conditions obtaining in the interior uranium 

 does not dissociate, or does so much more slowly. 

 It is even possible that it has not always proceeded 

 at this rate in the past. Radio-activity may be an 

 acquired habit of the substances that exhibit it. 



There is no scientific objection to the suggestion 

 that the existing "laws of nature" are not immutable 

 but "evolving," beyond the methodological incon- 

 venience that'this would greatly complicate our calcu- 

 lations and detract from the exactness of our predic- 

 tions. But of improbabilities, as of evils, we must 

 always choose the least. F. C. S. Schiller. 



Corpus Christi College, Oxford, June 23. 



Pianoforte Touch. 



Three variables appear to be possible in pianoforte 

 touch, namely : — 



(1) The energy of the blow of the hammer. 



(2) The duration of contact of hammer with wire. 



(3) The resonance of the woodwork. 



Of these, (1) will be admitted by everyone; (3) should 

 be in abeyance as much as possible, since it is brought 

 into evidence chiefly when the key is struck too hard — 

 beyond the capacity of the wire for harmonic response. 

 But the mechanism of some pianos (even by first-class 

 makers) is so resonant that a " xylophone " effect is 

 only too easily produced. This effect evidently has its 

 admirers, being cultivated by performers as well as 

 ministered to by piano-makers. 



(2) Is assumed by many persons ; but the possibility 

 is doubted by others, because the player cannot hold 

 the hammer in contact with the wire. The hammer, 

 as mentioned by Prof. Bryan, is disconnected from 

 the key, so that at the time of striking the wire it is 

 a projectile. 



At some point in the mechanism, between the key 

 and the hammer, is an arrangement called the 

 "escapement," which disconnects the key from the 

 hammer when the player's touch is so deep or firm 

 as to cause the risk of blocking; but when his touch 

 is shallow the escapement is scarcely brought into 

 action. 



