240 



NATURE 



[February 23, 1922 



If only the largest constituents had been used the task 

 of analysing for the remainder would have been made 

 more onerous by the presence of this error, and much 

 more so if there were unknown constituents to deal 

 with. 



I quite agree with Mr. Marnier that the only satis- 

 factory method of testing the machines is to compare 

 their results with the results of numerical or "hand " 

 calculations, but such tests should be exhaustive and 

 convincing. A. T. Doodson. 



Tidal Institute, University of Liverpool, 

 Februar/ 9. 



The Brittleness of Ice at Low Temperatures. 



Sir George Beilby (" Aggregation and Flow of Solids," 

 192 1) has recently directed attention to the impossibility 

 of explaining the flow of glaciers at temperatures 

 much below 0° C. on the regelation hypothesis, and 

 the necessity for assuming a deformation of the ice- 

 crystals by displacement along internal-glide planes 

 or at the crystal boundaries. From his experiments 

 on the behaviour of metals and minerals under pres- 

 sure he suggests that in ice a vitreous modification 

 will be produced at the plane of displacement, and 

 that above a certain temperature — the "crystallisation 

 temperature " — this will immediately revert to the 

 crystalline state, the process being repeated indefinitely 

 during movement. Should the temperature of the ice 

 fall below this point it is predicted that the flow will 

 be retarded, as the vitreous modifications of metals 

 are harder than the crystalline, and their presence 

 promotes rigidity. 



It seems that here we have an explanation of the 

 brittleness of ice at low temperatures. Navigators in 

 the pack have noticed that the development of the 

 pressure ridges is noiseless in summer, but accom- 

 panied by loud detonations in winter. Another con- 

 sequence of the existence of this state at low tem- 

 peratures is well known to every ski-runner in a dis- 

 tinct loss of gliding power. Sir George Beilby has 

 shown that the "crystallisation temperature" for ice 

 must lie sornewhere below - 12° C. There is general 

 agreeinent in Norway that the "f0re," though 

 deteriorating slowly as the temperature falls below 

 -5° C, receives a marked check at about -17° C, 

 and Nansen's observations in the pack are fairlv 

 consistent with this figure. To test the validity of 

 the explanation offered we must await the experi- 

 mental determination of the "crystallisation tempera- 

 ture " of ice. L. Hawkes. 



Bedford College, Regent's Park, N.W., 

 February 4. 



Age incidence of Influenza. 



Was not the unusual age incidence of deaths in the 

 influenza epidemic of 1918-19, referred to in Nature 

 of February 2, p. 130, due to the special circumstances 

 of that time? With few exceptions, all civilians in 

 this country at that date between the ages of twenty 

 and thirty-five could have been placed in one of three 

 classes : — 



(i) Persons engaged in war-work on the land, in 

 factories, offices, etc. All these were doing a full 

 man's working day (judged by the standard of normal 

 times), and many were seriously overworking. 



(2) Ex-Service men discharged on account of ill- 

 health. 



(3) Mothers of young children, who in many cases 

 went short of food themselves in order to ensure an 

 increased ration for their families. 



None of these would have been so resistant to 

 infection, or so well able to throw off disease when 

 contracted, as they would have been in normal times. 



Annie D. Betts. 

 NO. 2730, VOL. 109] 



Miss Betts suggests that the exceptional incidence 

 of influenza mortality during the pandemic of 1918-19 

 may have been caused by the exceptional war- 

 conditions, leading to the greatly increased occupation 

 of women, to overwork of these and of men, and to 

 the state of health of ex-Service men. To these sug- 

 gested causes may be added the effect of the rationing 

 of food, which might affect to an exceptional extent 

 the mothers of young children. 



These explanations of the strangely inverted age 

 incidence of influenza mortality have been often 

 debated. They cannot explain the course of events 

 more than to a minor extent. For (1) with such an 

 infectious disease as influenza domestic infection of 

 older persons, even when they had escaped extra- 

 domestic infection, must have been the general rule. 

 War-conditions must surely have told heavily on aged 

 persons. 



(2) Curves given on p. 41 of the Registrar-General's 

 Report on Influenza (Cmd. 700) show that this change 

 in age incidence was unparalleled in the history of 

 the disease, and that the changed age incidence 

 characterised the beginning of each of the three con- 

 secutive waves of the disease. With the progress of 

 each there was a diminishing youthfulness of 

 decedents. 



(3) This change in age incidence was not confined 

 to this country or to other belligerent countries 

 especially affected by war-conditions. It occurred, for 

 instance, in Scandinavian countries and in America. 



(4) The explanation that those attacked in the 

 1889-91 epidemic — the older section of the population 

 — were relatively irnmune is not supported by any 

 adequate body of evidence. 



In short, the altered age incidence of influenza in 

 the recent epidemic remains an unsolved problem. 

 An easy way out of the difficulty, though a way 

 probably not according with facts, would be to assert 

 that the recent pandemic was a diff'erent disease from 

 that of 1889-92. The Writer of the Article. 



Dr. Frank Bottomley. 



May I be permitted to make a correction of an 

 error in Sir Richard Paget's obituary notice of my 

 cousin, Dr. Frank Bottomley, in Nature of February 

 16, p. 212? Sir Richard states that Frank Bottom- 

 ley's stepmother was "the widowed sister of Lord 

 Kelvin." Frank Bottomley 's father, being a son of 

 Lord Kelvin's sister Anna, could not possibly have 

 married another of the sisters. Lord Kelvin had 

 three sisters, namely, Elizabeth, widow of the Rev. 

 David King (she never remarried) ; Anna, Mrs. Wil- 

 liam Bottomley, who was Frank Bottomley 's grand- 

 mother ; and Margaret, who died in early childhood. 

 As a matter of fact, Frank Bottomley 's stepmother 

 was a sister of Lord Kelvin's second wife. 



James Thomson. 



22 Wentworth Place, Newcastle-upon-Tyne, 

 February 19. 



Thermo-electric Instrument for Measuring Radiation 

 from the Sky. 



In the note on Mr. W. H. Dines's memoir on 

 " Observations of Radiation from the Sky " (Nature, 

 January 12, p. 54) you attribute to me the final 

 design of the Instrument. Permit me to say that 

 Mr. Dines greatly elaborated and improved the 

 thermo-electric instrument after I left It. 



Lewis F. Richardson. 

 Westminster Training College, 



Horseferry Road, S.W.i. 



