March io, 1892] 



NATURE 



441 



their condition of equilibrium. The greater part of the recovery 

 takes place in the first week, and a considerable part in the 

 course of the first day." 



Now I have little doubt that both the want of accordance in 

 the readings of the instrument with decreasing and then with 

 increasing pressure, and the " after- working" mentioned above, 

 are mainly, if not entirely, due to the imperfect elasticity of the 

 corrugated disk that forms the cover of the exhausted chamber. 

 No metal is perfectly elastic except with very minute stresses, 

 and, as a consequence, when a metal is made to go through a 

 complete stress cycle, there is always more or less lagging of 

 strain behind stress. Again, there is with all metals more or less 

 of time-lag, so that any alteration of stress does not produce its 

 full effect all at once. Provided the temperature be kept con- 

 stant, and the metal be not in any way disturbed, the time-lag is 

 of such a nature that for equal successive intervals of time the 

 corresponding changes of strain form a descending geometrical 

 progression. With some metals, such as tempered steel, and 

 with moderate stresses, the effects of imperfect elasticity are not 

 of any material consequence. With others, however, such as 

 aluminium and zinc, and the alloys of the latter metal — namely, 

 brass, German-silver, &c. — we meet with very appreciable 

 deviations from the laws of perfect elasticity, even when the 

 stresses used do not produce any permanent deformation. I 

 understand that the corrugated cover is frequently made of an 

 alloy something like German-silver, only softer. If this be so, 

 I can well believe, from my experience of this alloy, that grave 

 errors might arise, and probably have arisen, in the determina- 

 tions of heights by the aneroid. If such a thing be feasible, 

 I would suggest that the cover should be made of tempered 

 steel. Herbert Tomlinson. 



King's College, Strand, February 19. 



Sparrows and Crocuses. 



The time of year has arrived when we shall once more be 

 hearing of the ravages of sparrows on crocus blooms, and the 

 theories advanced in order to account for this propensity for 

 destruction on the part of the sparrow in suburban gardens and 

 elsewhere. One pet theory is that the sparrow has a fondness 

 ior yellozc, and shows it by destroying crocuses of that colour. 

 Most unfortunately for the holders of such an opinion, the 

 sparrow does not confine its attentions to yellow crocuses only, 

 but attacks also the purple, white, &c., as any grower of 

 crocuses can prove. Undoubtedly the yellow suffer most, 

 probably because they are the first to appear, and meet the 

 birds' most pressing requirements. Moreover, the sparrows 

 sometimes attack the flowers while still in the sheath, and before 

 it is certain what colour they will be. 



The object of the sparrow in destroying the flowers is simply 

 to obtain succulent food at a time of year when such in the form 

 of larvae, &c., is scarce. I have repeatedly watched the opera- 

 tion from my study window at a distance of very few feet. 

 The stalk of the flower is bitten off by the bird some little 

 distance below the flower itself. The succulent stalk is then 

 nibbled away until the flower falls to pieces. The reproductive 

 parts, and especially the anthers are not attacked, as some 

 writers have asserted ; but in consequence of the structure of 

 the flower, they, like the petals and sepals, often fall away owing 

 to the close nibbling of the bird. 



Primroses also suffer. Early primroses are usually the common 

 yellow form, ergo, according to theory-makers, the same cause 

 is at work. So it is, but not in the direction they would have 

 us believe. Here, again, I have distinctly seen the birds eating 

 the flower-stalk. 



I had written you a letter to the same effect as this about the 

 same time last year, but from some cause or other it was not 

 forwarded. I take this opportunity of possibly anticipating 

 other letters on the same subject, and of inducing theorists to 

 carefully watch the modus operandi as I have done before rushing 

 into print. K. McLachlan. 



Lewisham, February 26. 



A Possible Misunderstanding, 

 I HAVE seen a report that, in a recent number of the Alti 

 dclla Kegia Academia delle Scienze di Torino, Prof, Galileo 

 Ferraris is credited with a statement which might mean that one 

 of the formulas which appear in a paper read by me before the 

 Physical Society of London, in May 1888, was derive 1 from a 



paper by him. If that be Signor Ferraris's meaning, he is 

 entirely mistaken. My formulae were obtained quite independ- 

 ently of Signor Ferraris or of anyone else, 



Thomas H. Blakesley, 

 Royal Naval College, February 29. 



NO. II 67, VOL. 45] 



HERMANN KOPP. 

 TJERMANN FRANZ MORITZ KOPP, a distin- 

 ^-*- guished German chemist, and one of that band 

 of literary and scientific workers which, five-and-twenty 

 years ago, made Heidelberg celebrated as a -centre of 

 intellectual activity, passed away from the scene of his 

 labours on February 20, in the seventy-fifth year of his 

 age. He had been in failing health for some time past, 

 and although his recuperative power at times seemed 

 wonderful, his friends were not wholly unprepared for 

 his decease. 



Born October 30, 1817, at Hanau, where his father, 

 Johann Heinrich Kopp, practised as a physician, Hermann 

 Kopp received his school training at the Gymnasium of 

 his native town, and thence passed to the Universities of 

 Heidelberg and Marburg with the object of studying the 

 natural sciences, and more particularly chemistry. The 

 special bent of his mind towards chemistry would seem 

 to have been given by his father. The elder Kopp occa- 

 sionally busied himself with experimental chemistry, and 

 Leonhard's Taschenbuch and Gehlen's Journal contain 

 papers by him on mineral analyses and on investigations 

 relating to physiological chemical products. 



In 1839, Hermann Kopp joined Liebig at Giessen, 

 drawn thither by the extraordinary influence which has 

 made the little laboratory on the banks of the Lahn for 

 ever famous in the history of chemical science. For 

 nearly a quarter of a century Kopp found in Giessen 

 full scope for his scientific and literary activity. In 1841 

 he became a privat-docent in the University, two years 

 later he was made an extraordinary professor, and in 

 1853 he became ordinary professor. In 1864 he was 

 called to Heidelberg, where he remained until his death, 

 occupying himself latterly with lectures on the history of 

 chemistry, and on chemical crystallography. 



At the very outset of his career as an investigator, 

 Kopp seems to have devoted himself to that field of 

 inquiry in which his chief distinction as an original 

 worker was won, viz. physical chemistry. One of his 

 earliest papers — " Ueber die Vorausbestimmung des 

 specifischen Gewichts einiger Kiassen chemischer 

 Verbindungen," published in Poggendorff's Annaleti in 

 the year he went to Giessen — deals with the conception 

 of specific volume, which he here introduces for the first 

 time. During the ensuing five-and-twenty years, so far 

 as laboratory work was concerned, he was almost en- 

 tirely occupied in attempting to trace experimentally 

 the connection between the physical properties of sub- 

 stances and their chemical nature. We owe to Kopp, 

 in fact, all our broad fundamental generalizations con- 

 cerning the connection between the molecular weights, 

 relative densities, boiling-points, and specific heats of 

 substances, and on the relations of crystalline form and 

 chemical constitution to specific volume. For work of 

 this kind Kopp was eminently well fitted. To remark- 

 able manipulative dexterity and great ingenuity — much 

 of which, as in the case of Wollaston, was spent in satis- 

 fying a certain fastidiousness for simplicity of apparatus 

 and experimental method — was Joined the most scrupu- 

 lous sense of accuracy and illimitable patience. As proof 

 of his accuracy, it may be stated that, although many 

 observers have had occasion, from time to time, to review 

 his work on the thermal expansion of liquids — and on a 

 far more ambitious scale, ancl with more refined apparatus, 

 than was possible half a century ago — his determinations 

 have been practically unchallenged, and retain their place 

 among the best ascertained constants of their kind. 



