StPTEMllER 8, 1 910] 



NATURE 



-97 



specimens LOntaining 40 per cent, of autunite, obtained 

 direct from the minmg syndicate, having been ground up 

 together. From a fresh batch, obtained through a dealer, 

 two single pieces were picked out, the first being an 

 almost pure crystal weighing 2-3 grams, and of so fresh 

 and new appearance that it looked as if it had been with- 

 drawn from its mother-liquor but yesterday, and the 

 second an obviously older looking, greener, and much 

 larger mass containing 46 per cent, of matri.x. The first 

 gave a radium ratio of 70 per cent., and in it helium 

 could not be detected. The quantity was not greater than 

 O'O02 cu. mm. per gram U. This quantity would form 

 in about thirty years ! For the second, the radium ratio 

 was 44 per cent, and the helium 0-035 c"- "''"''• P^"" gram 

 L , which would be produced in about boo years. Lastly, 

 Mr. Russell very kindly gave me the remains of the 

 specimen for which he found 27 per cent, for the radium 

 ratio. It 'Weighed less than 0-5 gram, but the helium was 

 easily detectable. It amounted to more than 0.15 cu. mm. 

 per gram U, some being lost. 



If these results are representative, the radium ratio 

 decreases to a minimum and then rises more slowly as 

 the helium content increases. If the latter is taken as a 

 measure of the age of the mineral, the minimum appears 

 to be reached after a few thousand years. This, of course, 

 is exactly what would occur if, when the autunite was 

 formed, the radium {but not its parent) associated with the 

 uranium in its former condition separated with the latter. 

 This in itself is not only possible, but probable, owing to 

 the isomorphism of radium and calcium. But it is a 

 somewhat startling result if initial radium can have any 

 influence on the amount present in a mineral to-day, for 

 this necessitates that the ages indicated by the helium 

 content are not altogether below the truth, and that these 

 beautiful crystals are actually even now in full process of 

 formation. Frederick Soddv. 



Physical Chemistry Laboratory, University of 

 (ilasgow. 



Stagnant Glaciers 



In the notice of the Professional Papers of the U.S. 

 Geological Survey on the " Glaciers, Goldfields, and Land- 

 slides of North -America," published in Nature of July 21, 

 attention is directed to the peculiar stagnant condition of 

 some glaciers, and to the fact that certain glaciers, after 

 being stagnant for long intervals, suddenly commence to 

 move. 



.Mthough the movement of glaciers is such as would 

 tak'> place if they were viscous bodies, there is reason to 

 believe that they have not all the same viscosity. I 

 painted out in a paper communicated to the Royal Society 

 (Proc. Roy. Soc, 1908, p. 250) that the calculated viscosi- 

 ties of several Swiss glaciers varied from 292-2X10"' to 

 3-I7XIO'- C.G.S. units. Although some of the data upon 

 which these figures were based were only estimated ones, 

 I do not think that the different viscosities found are due 

 wholly to errors in the data. In other words, that the 

 viscosity of glacier ice is not a constant, as in the case 

 of water, &c., but varies with variations in the granular 

 structure of the ice, or that there is a limiting stress below 

 which distortion does not take place as with plastic bodies. 



.So far as I am aware, no glaciers have been proved 

 actually to be stagnant by careful measurement. Gener- 

 ally speaking, the conclusion that a glacier is dead is 

 formed owing to the absence of certain features which 

 are generallv associated with glacier movement. 



It is very desirable that such statements should be based 

 upon actual measurements only, and also that the actual 

 granular structure of the ice should be given, for there 

 is every reason to believe that the viscosity of glacier ice 

 varies with the size of the glacier grains. Were it not 

 for the fact that the glacier grains are actually broken 

 up by shear planes in the ice, they would gradually become 

 larger and larger until they became so large, and the 

 viscosity became so great, that the ice would scarcely 

 move at all on small slopes. In such a case an earth- 

 quake might give rise to fractures in the ice, and by 

 temporarily decreasing the viscosity increase the rate of 

 flow. R. M. Deelev. 



Melbourne House, Osmaston Road, Derby, July 23. 



NO. 2132, VOL. 84] 



It chanced, strangely enough, that Mr. Deeley's interest- 

 ing letter reached me at a Norwegian port during the 

 return journey of the Geological Congress party from 

 Spitsbergen, on which Prof. R. S. Tarr, whose work has 

 given rise to the letter, is a fellow-traveller with me. I 

 have therefore taken advantage of the opportunity to 

 discuss the subject with Prof. Tarr and other glaciaHsts 

 of our party. 



Mr. Deeley is right in his supposition that the stagnant 

 condition of the " dead ice " in Alaska has been inferred 

 from surface indications, and has not yet been tested by 

 actual measurement. It is, indeed, not likely that the ice 

 of the areas described as " stagnant " is absolutely 

 motionless, nor do I think that this has been implied in 

 the descriptions. Such motion as it may have must how- 

 ever be very small, since it seems that the trees covering 

 parts of the surface-moraines in the " dead " areas show 

 no sign of disturbance. 



.As hinted in my review, it is evident that rapid advances 

 of glaciers, comparable to those observed in Alaska, have 

 taken place in regions where some other cause than an 

 earthquake must be sought. During our recent journey 

 in Spitsbergen, of which I hope shortly to give some 

 account in these pages, we have been shown by our 

 leader. Prof. G. de Geer, several cases of this kind which 

 he has studied. It may be that Mr. Deeley's explanation 

 of ice-structure will explain these rapid spasmodic move- 

 ments, but I shall not venture upon a discussion of this 

 diflicult physical question. Mr. Deeley has at any rate 

 suggested a line of research which ought to be followed 

 up and experimentallv tested in the field. 



Stockholm, August' ici. G. W. Lamplugh. 



The Leaning Tower of Pisa. 



The photograph of the " Leaning " Tower of Pisa in 

 Nature of .August 4 shows clearly that the top tier is not 

 square with the rest. From a rough alignment with the 

 edge of a postcard, the photograph appears as if the tower 

 was of the order of 25 mm. /metre out of plumb when the 

 top tier was put on presumably plumb. 



Exact measures of this and _of other parts of the tower 

 might afford interesting data" as to the epochs of the 

 construction of the tower and of the progress of its 

 " leanino." Edward G. Brown. 



This famous tower will doubtless always be a question, 

 like the man in the iron mask and other historical 

 mvsteries. Most architects, however, will be very slow to 

 believe that it would have been built intentionally leaning 

 on the general grounds that, however adventurous the 

 architect, the clients would not have stood it. The analogy 

 of the leaning towers of Bologna is hardly a sound one. 

 as these plain shafts of brickw^ork, much like tall chimneys, 

 can hardly be other than cases of settlement due to in-- 

 different foundations. It should be remembered that con- 

 struction was not a strong point with the Italians in the 

 Middle and Renaissance .Ages. In the case of the Tower 

 of Pisa, Tavlor particularly remarks on the wedge-shaped 

 courses, which show an attempt to straighten the shaft. 

 The best explanation appears to be that the tower was 

 commenced, settled on its marshy bed, and that when 

 the building was continued after a long interval it was 

 considered safe to continue the w-ork up to the limit of 

 stabilitv which could be calculated by the mathematicians 

 of the epoch. The overhang is given by Taylor as 13 feet. 



It is rather a pity that so much attention is concentrated 

 by visitors on the' tower, whereas the cathedral, Campo 

 S'anto, and particularly the Baptistery, are monuments of 

 greater architectural importance. The design of the 

 Baptistery is extremely interesting, and is perhaps the 

 nearest expression of a Gothic dome. 



The construction in this case is highly interesting, 

 because the outer dome is supported by a cone, as at St. 

 Paul's, London, but without an inner dome. ^ As,_ how- 

 ever, the cone is not illuminated from the inside, it has 

 a domical effect. The top of the cone shows externally, 

 to the detriment of the general outline, not being cut off 

 to carrv a lantern as at St. Paul's. 



