174 



NATURE 



[December 20 1900 



" About twenty years ago " (the quotation is from the 

 catalogue of the German Instrument Exhibition at Paris) 

 "the manufacture of thermometers had come to a dead 

 stop in Germany, thermometers being then invested with 

 a defect, the hability to periodic changes, which seriously 

 endangered German manufacture. Comprehensive in- 

 vestigations were then carried on by the Normal Aich- 

 ungs-Kommission, the Imperial Physical and Technical 

 Institute, and the Jena Glass Works, and much labour 

 brought the desired reward." 



Dr. Hovestadt's account of the labour is most interest- 

 ing and instructive. 



The ice point of a newly made mercury thermometer 

 is known to rise as the thermometer gets older ; this rate 

 of rise decreases with the time, finally becoming very 

 slow. If, however, the thermometer be heated to, say, 

 100° C, and its ice point be taken very shortly after- 

 wards, the reading will be below that observed prior to 

 the observation of the steam point. This depression of 

 the zero varies in amount in diflferent thermometers. It 

 was found (Weber in 1883 and Wiebe 1885- 1886) to be 

 specially large in the case of thermometers made of 

 Thuringian glass, amounting in the case of one ther- 

 mometer examined to o°-65. As a consequence, the 

 readings of the thermometers were quite uncertain, 

 depending greatly on the past history of the instrument 

 employed. It was this defect which Schott and Abbe 

 set out to cure. Weber had observed that glasses which 

 contained a mixture of potash and soda gave a very large 

 depression. He succeeded in 1883 in making a glass 

 entirely free from soda, in which the depression was only 

 about o°'i. The work was then taken up by the Aichungs 

 Commission and the Jena factory. A number of ther- 

 mometers of varying age and manufacture were examined 

 as to the depression, and the glass of these thermo- 

 meters was then analysed. Weber's conclusions were 

 abundantly verified. An old thermometier of Humboldt's, 

 containing o'86 per cent, of NajO and 20-09 per cent, of 

 K2O, had a depression of o°'o6 ; a new instrument, in 

 which the percentages of the two substances respectively 

 were 1272 and io'57, had a depression of o''-65. It is 

 possible that this last thermometer was too new to give 

 quite trustworthy results, but the difference is very marked. 

 An English standard thermometer, with i"54 percent, of 

 NagO and 1226 per cent, of KjO, had a depression of 

 o°*i5, while a French " verre dur" thermometer, with 

 i2'o2 of NagO and 0-56 of KgO, showed a depression of 

 only o°'oo8. 



The next step was to manufacture a German glass 

 with a low depression. The now well-known normal 

 thermometer glass distinguished by the mark 16"' was 

 the outcome of the experiments. This is a pure soda 

 glass having the following composition : — 



SiOj, 67-57,; NajO, I47„; CaO, 77„ ; AI2O3, 2-57„; 

 ZnO, 77c ; B2O3, 27„, 



and the depression observed is o°"05. 



The hydrogen thermometer is, however, the ulti- 

 mate standard of appeal in thermometry, and it was 

 necessary, therefore, to compare the new instruments 

 with such a thermometer. 



Details of the work are given in the book. It appeared, 

 from the results of Wiebe and others, that at a tempera- 

 NO. 1625, VOL. 63] 



ture of 40° there was a difference of o'^'i2 between the 

 two nstruments. Experiments showed, however, that it 

 was possible to produce a glass agreeing more closely 

 with the gas thermometer than this, and this fact led 

 to further work and to the manufacture of the boro-sili- 

 cate glass 59'" with the following analysis : — 



SiOa 727o ; Na^O, 117, ; AI2O3, 57, ; B2O3, i2°/„. 



This was found to show a smaller ice point depression, 

 amounting, according to Hovestadt, to o°*02, and to 

 agree more closely over the range 0° to 100° with the 

 hydrogen thermometer, the difference being greatest at 

 30°, where it amounts to o°*038. For temperatures above 

 100" the differences are considerably greater than those 

 given above, and the agreement between the scales is 

 better for 16'" than for 59'". 



For details, however, of these comparisons, and of 

 much more work of great interest as to the properties of 

 these special glasses, reference must be had to the book. 

 It constitutes a great record of what is to be achieved by 

 the application of science, that is, " organised common 

 sense " to an important industry. In England we have 

 done nothing to compare with it. As a consequence, 

 Germany can claim that "the manufacture of thermo- 

 meters has reached in Germany an unprecedented level, 

 and now governs the markets of the world." Such are 

 the results obtained in twenty years by Abbe and his 

 colleagues. R- T. G. 



ESSAYS BY DR. WALLACE, 



Studies^ Scientific and Social. By Alfred Russel Wal- 

 lace. 2 vols. Illustrated. (London : Macmillan and 

 Co., Ltd., 1900.) Price i8j. 



IN addition to bemg one of the originators of the 

 modern doctrine of animal evolution and one of the 

 leading pioneers in the study of the geographical distri- 

 bution of the earth's fauna, Dr. Russel Wallace is a writer 

 noted for such a fascinating style and such a happy mode 

 of presenting his views, that any work from his pen is 

 sure of a hearty reception on the part of the more thought- 

 ful section of the reading public. And even those who 

 by no means agree with all his views — whether on scien- 

 tific or social questions — cannot fail to admire the fairness 

 with which he treats debatable points, and the temperate 

 manner in which he replies to and discusses the objec- 

 tions raised by his critics. 



The essays and articles collected in the two volumes 

 before us embrace an extraordinarily wide range of sub- 

 jects, and cover a period of no less than thirty-five years, 

 the earliest of them being published as long ago as 1865, 

 while the latest saw the light as recently as 1899. The 

 variety of subjects discussed is alone a testimony to the 

 wonderful mental capacity of their talented author, while 

 the number of the periodical publications from which 

 they have been culled bears evidence to the popularity of 

 his writings. Those embraced in the first volume relate 

 exclusively to various branches of geological and biolo- 

 gical science, while those in the second are devoted to 

 educational, political, sociological and kindred subjects. 

 With the exception of a brief reference to two articles in 

 the second volume dealing with museums as educational 



