532 



NATURE 



[April 6, 1899 



not improbable that the expedition penetrated to the 

 region south of Khartum. The blocks are roughly 

 carved, and of course, whether from an artistic or his- 

 torical point of view, cannot be compared with the famous 

 reliefs of the expedition to Punt ; but ihey, at least, bear 

 witness to a foreign expedition of Pianchi that is not 

 elsewhere recorded. 



It will be seen, therefore, that Miss Benson and Miss 

 <;ourlayhave had some reward for their three seasons' 

 work ; and, although surface-excavation at Karnak is 

 not a very arduous or difficult undertaking, it is not un- 

 reasonable that they should be proud of having obtained 

 the first permission to e.xcavate given to women in 

 Egypt. Whether their example will be followed by 

 other ladies remains to be seen, though we think on the 

 whole such work is perhaps better left to the male 

 professional digger, who can camp on the spot, and 

 having a knowledge of Arabic is naturally better able to 

 control his men, and can check to some extent the thefts 

 of the smaller antiquities. Of the general plan of the 

 book in which Miss Benson and Miss (iourlay, with Mr. 

 Newberry's help, have published the results of their 

 work, one word must be said. The excavation of a 

 temple site, which results in correcting a previously 

 published ground-plan, and in recovering a number of 

 statues of secondary importance, is of the highest interest 

 to the expert, but does not appeal to the general public. 

 Yet Miss Benson has more than doubled the size of her 

 book by adding sketches of the religion and the history 

 of Egypt. In the preface it is stated that this has been 

 done for the benefit of those who, " without technical 

 knowledge, feel the fascination and interest of Egypt." 

 But for this class of reader it cannot be said that at the 

 present day there is any lack of sound popular histories. 

 In fact, in describing her diggings. Miss Benson should 

 have addressed herself only to the expert ; he would 

 have been contented with Parts ii. and v. of the book, 

 and the result would have been a very much handier 

 volume. 



OUR BOOK SHELF. 

 Die Medial-Fernrohre. By L. Schupmann. Pp. 145. 



(Leipsig : B. G. Teubner, 1899.) 

 EvKRY one is familiar in a general way with the optical 

 parts of a reflector and refractor, the former containing 

 in its optical series a parabolic reflector with a smaller 

 reflector and eyepiece, and the latter consisting of an 

 objective of two different kinds of glass for the elimin- 

 ation of colour, and the necessary eyepiece near the 

 focus. 



The "medialfernrohr" and " brachymedial-fernrohr," 

 both of which are discussed here, may each be described 

 generally as being a combination of a refractor and 

 reflector, for the functions of both an objective and a 

 curved reflecting surface are required. 



In the principle involved in this new method of con- 

 struction it is possible to produce an achromatic tele- 

 scope with the employment of only one kiiui of glass, 

 and the author, who had a telescope made as a pre- 

 liminary trial of the system he was investigating, says 

 " derartige Systenie hiitten also zur Not schon konstruiert 

 werden konnen, bevor man die verschiedene Dispersion 

 der Glasarten kannte." 



The achromatism in the telescopes here under discus- 

 sion is obtained by making the objective of one kind of 



NO. 1536, VOL. 59] 



glass, and, before the focus is reached, of intercepting 

 the light rays by a curved mirror near the surface of 

 which another lens of a different kind of glass is placed. 

 The light rays thus pass twice through the second lens. 



In these pages the author takes the case of tin 

 medialfernrohr first, and discusses the optics of it- 

 system very thoroughly, using terms in the discussion 

 which are generally considered inappreciable in othei 

 systems. The result of the investigation speaks very 

 highly for this class of instrument, and the greater the 

 aperture the more efficient does it seem to become. 

 It would naturally be thought that the employment of 

 two lenses and a reflector would tend to diminish very 

 considerably the brightness of the image, especially as 

 the rays pass twice through one of the lenses. We are 

 told, however, that comparing an ordinary refractor and 

 a "medial" of 12 cm. aperture, the brightness of the 

 image in the case of the former exceeds that of the latter 

 by 15 per cent. ; but comparing apertures of 34 cm., the 

 medial has the advantage of 7 per cent. For equal 

 apertures of i metre the " medial " exceeds the refractor 

 by as much as 30 per cent. 



Towards the latter part of this volume the author 

 describes the method of mounting and adjusting an 

 instrument of large dimensions. He then discusses the 

 "brachyniedial " telescope, adapting the formulae ob 

 tained in the previous portion of the book to this form ol 

 instrument. Here he also describes a telescope of large 

 aperture on this principle, but although optically it 

 does not attain the efficiency of the " medial,'' yet the 

 fact, that the length of the tube is very considerably 

 shortened by a more compact arrangement of the optical 

 parts, may counterbalance this deficiency. 



In conclusion, we recommend to our astronomical 

 and physical readers the work before us ; for it is only by 

 such investigations that further advance in our present 

 instrumental equipment can be made. 



Mathcmuticil and Physical Tables. By James P. 

 Wrapson and W. W. Haldane Gee. Pp. viii -f 215. 

 (London : Macmillan and Co., Ltd., i8qS.) 

 In these pages the compilers have brought together a 

 most useful set of tables and formula? which should be 

 found of great service, both in the class-room and labor- 

 atory. The first part of the book is devoted simply to 

 tables : these include, among others, four-place logarithms 

 and antilogarithms, natural and logarithmic sines, cosines, 

 and tangents, tables of squares, square roots, cube roots, 

 &c. In the next section the reader has brought before 

 him the chief formuhc in pure and applied mechanics ; 

 here, for example, he can find at a glance the lengths of 

 curves, areas and volumes of solids, plane and spherical 

 trigonometrical formuho, formula; used in analytical 

 geometry, and others connected with dynamics, pendu- 

 lums, elasticity, and hydraulics. 



The other sections, the contents of which are too 

 numerous to mention, consist of tables of pure and 

 applied physics, which should be found very useful, 

 and formul.i in pure and applied physics, which include 

 optics, heat, magnetism, electrostatics, electro-chemistry, 

 electro-magnetic induction, and alternating currents, &c. 

 The volume concludes with an appendix containing 

 other useful miscellaneous information, and an index. 



If the book be used judiciously, and employed simply 

 as a means of reminding the student of formula- and data 

 which may have grown rusty by disuse, its value is to be 

 recommended ; but it should not be given to young 

 students, who would probably work out problems without 

 knowing the why and wherefore of the expressions they 

 are using. 



For neatness and conciseness, and the numerous 

 clearly printed diagrams, the volume will be found a 

 desirable source of information, and considerable pains 

 seems to have been taken to bring the data up to date. 



