NA TURE 



[May 4, 1905 



one hand, and with carbon and hydrogen on the other, as 

 in the explosives, e.g. nitroglycerine. 



Living substance has apparently all the above mentioned 

 sources of instability, and perhaps not the least important 

 is that it has for its pivot nitrogen, the element which 

 above all others is remarkable for the lability of its com- 

 pounds. I have elsewhere ' indicated the probability that 

 the active molecule of living substance consists of an 

 enormous complex of proteids, carbohydrates, &c., linked 

 together by means of the nitrogen atoms, and that the 

 oxygen store is more or less combined with the nitrogen. 

 At the death of the molecule its constituent groups (pro- 

 teids, &c.) are released, and the store of oxygen passes 

 from the nitrogen into other and more stable forms of 

 combination. F. J. Allen. 



Cambridge. 



Chalk Masses in the Cliffs near Cromer. 

 At the present time the cliffs near Cromer exhibit some 

 interesting chalk masses in the Glacial drifts. Between 

 East and West Runton Gaps are several of great size and 

 remarkable in position. One, a very long slab-like mass, 

 is bent from being nearly horizontal until it is almost 

 vertical, and thus comes to within a short distance of 

 the top of the cliff. The masses near Tritningham will 

 now repay a close study, for they have changed greatly 

 during the last five years. Both my friend, the Rev. E. 

 Hill, and I have made notes and rough sketches, with the 

 intention of sending to the Geological Magazine a short 

 account of what can now be seen ; but we earnestly hope 

 that some geologists who are adepts at photography will 

 visit both localities at the earliest possible opportunity, in 

 order to secure a permanent and accurate record of these 

 exceptionally interesting sections. T. G. BoNNEV. 



The Rigidity of the Earth's Interior. 



The letter of Ur. T. J. J. See (Nature, April 13, p. 559) 

 deals with a subject of profound interest to students of 

 the larger problems connected with physical geology. But 

 it appears that, in Dr. See's treatment of the subject, he 

 has overlooked an important point, which I dealt with in 

 a paper read before Section C of the British Association 

 at Birmingham in 1886. Therein I directed attention to 

 the fact that " gravitation " is only a special instance of 

 the law of universal attraction, and as a corollary to 

 this, at any considerable depth within the sphere of the 

 earth, an appreciable factor of what I may call negative 

 gravity must be allowed for, owing to the counter- 

 attraction of the mass of matter situated nearer the surface 

 of the sphere ; so that a body placed at the centre of gravity 

 of the earth, whatever its mass or density, would have no 

 weight at all. 



I am glad to see that the consideration of " critical 

 temperatures " of quasj'-solids (the importance of which 

 was emphasised in my little work on metamorphism 

 some fifteen years ago) is receiving serious attention, and 

 I may also point out that the idea of a potentially liquid 

 (or even gaseous) condition of a mass at depths in a 

 practically rigid state is not new ; it was treated in a 

 masterly way by Prof. Albert Heim, of Ziirich, some 

 twenty years ago, in his magnificent work " Ueber den 

 Mechanismus der Gebirgsbildung. " " Ueberlastet " is the 

 word used by Heim to express such conditions, where the 

 pressure is so far " hydrostatic " as to consist of com- 

 pression acting equally (for the time being) in all direc- 

 tions. Any disturbance in a given portion of the litho- 

 sphere of the equilibrium thus existing must result in 

 shearine; movement if the disturbance be small, and in floit! 

 in a given direction if the relief in that direction from 

 pressure is great and rapid enough. In the former case 

 we should get " metataxic change," in the latter 

 schistositv ; for I still challenge the statement, made 

 recently by a high authority, that " it is only a question 

 of degree between the cleavage of a slate and the foliation 

 of a crystalline schist or gneiss." 



Questions relating to tidal action in the rotating litho- 

 sphere, and even Lord Kelvin's oft-repeated objection on 



I Report Brit. Assoc, 1896, p. aSs ; and Pror. BiniiiiiFliam Nat. Hhl. 

 and Pkilof. .';oc., liaa. ' ' 



NO. 



T853, VOL. 72] 



that ground to the impossibility of any considerable por- 

 tion of the lithosphere being fluid, because the earth does 

 not undergo the deformation which the physicist would 

 expect owing to the tidal action which should be set up 

 within it, might possibly be seen in a fresh light on taking 

 into account the remarkable facts demonstrated by Prof. 

 John Perry in his lecture on spinning tops, which he gave 

 to an audience of working men on the occasion of the 

 meeting of the British .Association at Leeds in 1890. As 

 a " working man " in a real sense of the word, I con- 

 sidered myself privileged to attend that lecture, and was 

 rewarded by finding in my own mind a great difficulty 

 cleared up by Prof. Perry's masterly demonstrations of the 

 practically rigid condition of non-rigid bodies, if only made 

 to rotate with sufficient rapidity, as the equatorial regions 

 of the earth do — something like 1000 miles an hour. 

 Bishop's Stortford, April 17. A. Irving. 



of1|| 



Rival Parents. 



\ CURIOUS example of the rival claims of a pai 

 thrushes and a pair of blackbirds for the parentage 

 young blackbird is being observed in my garden. 



A pair of blackbirds built a nest in a small thick laurel, 

 and in another shrub, some 4 feet off, a pair of thrushes 

 also built a nest. The young in both nests were hatched 

 out at the same time, and were successfully reared until 

 they were some eight or nine days old, when a cat attacked 

 the nests (Monday, April 17), killing all the young thrushes 

 and all the blackbirds e.xcept one, which was found hidden 

 under the shrubs. It was continually visited after the 

 tragedy by both the old thrushes and old blackbirds, and 

 two or three hours later was removed in some way not 

 observed to a shrubbery twenty or thirty yards away. 

 There for the last five days it has been fed and looked 

 after bv both pairs of birds, who mob with exceptional 

 vigour any intruding cat or dog. The young bird seems 

 to have thriven mightily under the attentions of its true 

 and foster parents, who appear in no way to be jealous 

 of one another. Kennedy J. P. Orton. 



University College of North Wales, Bangor, April 21. 



The Measurement of Mass. 



In the notice of my little book, " Radium Explained," 

 iin .'\pril 6, twenty-nine lines are devoted to showing that 

 I have reached a wrong conclusion through not knowing 

 that muss is measured by inertia, and I am corrected in 

 these words : — " how is the quantity of matter to be ascer- 

 tained? The choice practically lies between defining mass 

 by inertia at a given speed or by gravity. . . . As, however, 

 gravity depends on local circumstances, while inertia (at 

 given velocity) does not, the latter property is preferred 

 for the definition of mass, as being more fundamental." 

 .So far from rejecting this principle, I state it, in almost 

 the . same terms, on p. 84 of my book : — " Mass, or 

 quantity of matter, is usually ascertained by weighing. 

 But weight is merely the force with which the earth 

 attracts, and this varies with our position on its surface. 

 To get an absolute test of mass, which would be in- 

 dependent of position, we may measure the force required 

 to move or stop a body at a certain speed." .And nowhere 

 in the book have I supported any argument by the re- 

 pudiation of the principle here clearly stated. This is a 

 question of fact ; the other objection taken is equally ill- 

 founded, but, being on a controversial point, it cannot be 

 dealt with so briefly. W. H.^MPSOX. 



West Ealing, May i. 



Properties of Rotating Bodies. 



Prof. W. H. Pickering, in Nature of April 27 (p. 608), 

 refers to the property which a rotating body possesses of 

 assimilating, in certain circumstances, its axis of rotation 

 to a secondary axis of rotation or revolution impressed 

 upon it, and he mentions the fact that this property is 

 rarely described. 



It was fully discussed in an elementary lecture given by 

 Prof. Perry at the Royal Institution about fifteen years 

 ago, and afterwards published in the Romance of Science 

 Series under the title " Spinning Tops." 



E. W. ROWNTREE. 



20 Queen Square, W.C., Mav i. 



