April 25, 1901 J 



NA TURE 



615 



thermal expansion of water between o° and 40°. To this 

 problem Regnault's method of measuring the thermal ex- 

 pansion of mercury is applied, with suitable modifications. 

 Elaborate precautions are taken to secure that the tem- 

 perature of each of the two balancing columns should be 

 the same throughout, but the difficulty of the measure- 

 ment lies in determining the difference in level of the 

 ends of these two columns, and Dr. Thiessen's apparatus 

 designed for this purpose proved in his hands most suc- 

 cessful. It may perhaps be useful to give the table of 

 the density of water at various temperatures under atmo- 

 spheric pressure, assuming the density at 4° C. to be 



unity- 

 Density Difference from 

 t- according to Thiessen. Chappuis' values. 



0° -9998676 - 2 



10 '9997270 + 2 



15 "9991263 .. +22 



20 -9982299 -1-29 



25 '9970715 +11 



30 '9956736 +19 



35 '9940576 +47 



40 -9922418 +43 



In the third column are given the differences between 

 Chappuis' values found in 1897 and those obtained by 

 Thiessen. 



It will be observed that throughout they are very smalls 

 indeed a closer examination shows that from 0° to 12" 

 the differences only amount to one or two units in the 

 seventh figure. Chappuis' measurements, it may be men- 

 tioned, were made by aid of a dilatometer of platinum- 

 iridium, and involve a knowledge of the thermal expansion 

 of that substance. 



In a second paper Dr. Thiessen applies to the same 

 apparatus for measuring the ' difference of height of two 

 columns to the determmation of the pressure of saturated 

 water vapour. The value found for this quantity at 0° C. 

 is 4'579 mm. of mercury, with a probable error of 

 'ooi mm. 



Another paper which should have many readers is that 

 by Profs. Jaeger and Kahle, on the mercury standards 

 of resistance. This is a continuation of Dr. Jieger's 

 paper in the second volume of the Transactiotis of the 

 Reichsanstalt. A very full description is given of the 

 work of constructing the standards and determining 

 by calibration their resistance in terms of the ohm as 

 defined legally, viz., the resistance of a column of mer- 

 cury at 0° C, 106-3 centimetres in length and I4'452i 

 grammes in mass. The tubes were then compared 

 electrically among themselves, and also with the man- 

 ganin standards of the Reichsanstalt. For this purpose 

 four manganin coils are used. The mean value of the 

 resistance of these four coils at 18° C, as determined 

 from the original tubes calibrated in 1892, was found 

 to be 1-004582, and from the new tubes calibrated in 

 1897, 1-004578. Changes amounting to about "00002 

 were observed in some of the manganin coils during 

 the period of observation. 



Dr. Kohlrausch himself contributes a very important 

 paper on the resistance of aqueous solutions of the 

 chlorides and nitrates of the alkalis. 



This is followed by a comparison of thermometers 

 made of various kinds of glass, with a further inter- 

 comparison of the standard thermometers of the 

 institution. 



As regards the depression of the freezing point, the 

 former observations of Wiebe and others are confirmed ; 

 it increases for the older kinds of glass, according to a 

 more or less parabolic law, with the temperature to which 

 the thermometer has been raised ; while, as before, it is 

 clearly shown that the depression is much greater in 

 glasses containing both soda and potash than it is in 

 glasses which contain either soda or potash only. 



Perhaps, however, the most striking results in the 



NO. 1643. VOL. 63] 



volume are those contained in a paper by Drs. Jaeger and 

 Diesselhorst on the thermal and electric conductivities, 

 the specific heats and thermo-electromotive forces of 

 certain metals. 



When a current passes through a conductor it is 

 heated ; when, however, a stationary state is reached, 

 the distribution both of current and of temperature does 

 not change with the time. The conditions for this in- 

 volve the ratio between the electric and thermal conduc- 

 tivities of the material, and Kohlrausch showed how this 

 ratio might be readily determined by observations on the 

 temperature and potential of three points of a conductor 

 carrying a constant current, provided the ends of the con- 

 ductor be maintained at a constant temperature. 



The theory and the experimental details are both fully 

 given in the paper ; the temperatures were determined 

 by the aid of very small thermal elements. The bars of 

 metal experimented on were in most cases about 27 cm. 

 in length, and from i to 2 cm. in diameter. The metals 

 examined included gold, silver and platinum, while bars 

 of rhodium and iridium, weighing respectively about -75 

 and 1-33 kilogrammes, were prepared by Herr Herseus, 

 but could not be used because of their extreme hardness. 



In addition to determining the electric and thermal 

 conductivities at 18^ and at 100^ C, the specific heats at 

 these two temperatures and their thermo-electromotive 

 forces as against copper were also determined. 



Attention had been called by Wiedemann and Franz, 

 in 1853, to the fact that the electrical and thermal con- 

 ductivities of many substances are approximately propor- 

 tional, and L. Lorenz, in 188 1, had shown that the ratio 

 of the thermal to the electric conductivities at various 

 temperatures is approximately proportional to the abso- 

 lute temperature. The experiments here described enable 

 us to test these laws. The ratio is shown not to be 

 accurately a constant, it varies in the case of the materials 

 tested, excluding constantan, from 636 for aluminium to 

 964 for bismuth, but in far the greater number of cases 

 its value lies between 670 and 800, a striking result when 

 it is recollected that the electric conductivities vary be- 

 tween 5 and 60. The temperature coefficient of the ratio 

 ranges, omitlmg bismuth and one or two high resistance 

 alloys such as constantan and manganin, from -034 to 

 ■046 ; if the Lorenz law were true it would be "0366 in all 

 cases. 



Sufficient, perhaps, has been said to indicate the im- 

 portance of the volume and the high value of the re- 

 searches which continue to be carried on at the Reichs- 

 anstalt. 



MEDIEVAL NATURAL HISTORY IN 

 POLAND.^ 



THERE are few more interesting occupations than to 

 trace the growth of scientific knowledge in the 

 field of natural history. We are heirs of the labours of 

 our forefathers, who were fain to struggle through 

 obscure and devious paths to build up the mass of 

 information on these subjects with which we are 

 furnished. We find them living in a wonderland of 

 the strangest credulity and superstition, and their errors 

 have only gradually disappeared in the process of 

 scientific investigation. With herbs, animals and 

 precious stones were connected the wildest theories. 

 Folk-lore played a busy part ; the mandrake uttered 

 groans when it was pulled up ; the toad had a jewel in 

 its head ; the barnacle was half herb and half animal, and 

 the barometz was a lamb which partook of a vegetable 



1 " Symbola ad historiam naturalem medii aevi. Sredniowieczna Historya 

 Naturalna. Systematyczne zestawienie roslin, zwierzat, mineralow oraz 

 wszystkich innego rodzaju, lekow prostych, uzywanych w Polsce od xii do 

 xvi w. przez Jozefa Rostafinskiego." ("Mediaeval Natural History. A 

 systematic account of the plants, animals, minerals and all kinds of simple 

 herbs known in Poland from the twelfth to the sixteenth century." By 

 Joseph Rostafinski. (Cracow : University Press.) 



