582 



NATURE [October ii, 1906 



figures in the former and two in the latter would be 

 iniple. Indeed, those familiar with insulation resist- 

 ance measurement will agree that to get results 

 concordant even in the exponent of lo, let alone the 

 significant figures, is not always easy with such 

 material as paraffin wax, and a much greater 

 accuracy in stating the measurement has, therefore, 

 no meaning. 



The illustrations, of which there are nearly 300, 

 are on the whole good, especially those of apparatus. 

 Among the illustrations, however, there are some 

 diagrams, such as Fig. 88, which are singularly poor, 

 ihieffy through faulty perspective drawing. 



The section on glow-lamps is good and up to date, 

 and includes a very full account of the construction 

 and use of vacuum pumps. The subject of arc-lamps 

 and of illumination is also well treated. The con- 

 cluding section, on the " production of electromotive 

 force " (induced voltage being, presumably, excluded), 

 contains an account of thermoelectric effects and of 

 primary and secondary cells, the latter being given 

 due prominence, as becomes their' importance to the 

 engineer. 



The descriptive portion of the work is throughout 

 very carefully written and illustrated. It is full of 

 representative information as to recent types of 

 apparatus. It will thus be seen that Mr. Parr has 

 placed before us a book on the elements of electrical 

 engineering which, if not satisfying from every point 

 of view, is nevertheless a good example of the type 

 of text-book which will introduce the student at once 

 to the theory and to the elementary practice of his 

 subject. D. K. M. 



COLLECTED WORKS OF ERNST ABBE. 

 Gcsammelte Ahhandlungen. Zweiter Band. By 

 E. Abbe. Pp. ii + 346. (Jena: G. Fischer, 1906.) 

 Price 7.50 marks. 



THE first volume of Prof. Abbe's works has already 

 been noticed in the pages of N.UURE (vol. Ixix., 

 •|j. 497). The contents of the second volume, while 

 extremely interesting, are more miscellaneous in their 

 character. The editors did well in collecting together 

 in one volume their author's epoch-making papers on 

 the theory of the microscope and his original papers 

 on optical problems. 



.'Kbbe's friends, however, will value the possession 

 of his complete writings, and the volume now under 

 review shows the width of his interests and the extent 

 of his knowledge. It opens with his inaugural 

 dissertation at Gottingen in 1861 on the experimental 

 foundation of the law of the equivalence of heat and 

 mechanical energy, a paper which deals chiefly with 

 the thermodynamics of a perfect gas so far as they 

 ran be deduced from the first law. This is followed 

 by two astronomical papers of somewhat local interest 

 communicated to the Frankfort Physical Association. 



The fourth paper is Abbe's dissertation on receiving 

 authority to teach in the philosophical faculty at 

 Jena in 1863, and is on the law of the distribution 

 of errors in a series of observations. 



Abbe's interest in optics was, as is well known, 

 NO. 1928, VOL. 74] 



first aroused by the request to help Carl Zeiss in his 

 construction of the microscope, and it is clear that as 

 a young man other branches of science attracted him. 



A paper reprinted from the Jena Zeitschrift fiir 

 Naturwissenschaft for 1874 follows, occupying some 

 eighty pages of the volume, and gives his own accoun; 

 of two of his best-known instruments. It is entitled 

 '" New .Apparatus for the Determination of Refractive- 

 Indices and Dispersion Constants," and in it are 

 described the .'\bbe refractometer and the method of 

 determining refractive indices by total reflection. 



The .\bbe refractometer is well known, and in the 

 skilful hands of the Jena firm has developed into ri 

 most useful and valuable instrument. Abbe's own 

 account of its development and of the reasons which 

 led him to its adoption are full of interest; it was 

 one of his earliest instruments in which the principle 

 of autocollimation was employed ; the light from the 

 collimator is made to fall normally on the second 

 face of the prism the index of which is required and 

 to retrace its path ; when this is the case the angle 

 of refraction is equal to the angle of the prism, and 

 can be easily measured ; the angle of incidence can 

 also be measured, and from a knowledge of the two 

 the refractive index is obtained. The principle which 

 forms the basis of the method described in the second 

 part of the paper has been further developed by 

 Pulfrich in his well-known total refractometer. 



Another interesting article is the first list of the 

 productions of the glass technical laboratory o'. 

 .Schott and Company at Jena, dated July, 1886. The 

 story of this work has often been told ; the growth 

 of the Jena firm in the twenty years which hav( 

 elapsed since the first list was published affords con- 

 clusive proof of the fertility of the union of the 

 mathematician who had the skill lo apply his know- 

 ledge in aid of the needs of industry and the manu- 

 facturer who realised that Abbe's science had a 

 commercial value, and could be made a factor of real 

 importance in the struggle for progress. 



The introduction to this first catalogue of optical 

 glasses opens thus : — 



" The industrial undertaking which is here first 

 brought before the notice of the public arose out of a 

 scientific investigation into the dependence of the 

 optical properties of solid amorphous fluxes on their 

 chemical composition which was undertaken by the 

 undersigned with a view to bring to light the chemieo- 

 physlcal foundations of the production of optical 

 glass " — 



and though at present there are many problems which 

 confront the glass maker, thanks to the researches 

 of .\bbe and Schott the knowledge of 1906 is far in 

 advance of that of 1886, 



Enough has perhaps been written to show the 

 interesting character of the book. Among the other 

 papers are accounts of some of the various apparatus 

 designed by Abbe, including the now well-known 

 prism binocular, and some reviews and notices, both 

 of books and men. Of these, perhaps the most 

 noticeable is an address delivered in the hall of the 

 Physical Institute at Jena on March 5, 1887, to com- 

 memorate the centenary of the birth of Fraunhofer, 



