444 



SCIENCE. 



[Vol. IV., No. 92. 



the cuneiform inscriptions of western Asia. This 

 contains a great deal of linguistic and historical ma- 

 terial ; e.g., a list of four hundred and eighty Assyrian 

 verbs so arranged as to show an aquaintance with an 

 alphabet on the part of the writer. We find, first, a 

 series of groups of verbs whose first and second con- 

 sonants are the same; and, secondly, within these 

 groups, they are arranged according to their final 

 consonant. This is the first inscription showing 

 alphabetic order, and the alphabet is substantially 

 the same as the Hebrew. Unfortunately the tablet 

 is not dated. There is also an historical tablet of 

 Nabunaid or Nabonetus, who was king when Cyrus 

 took Babylon. Nabunaid tells how he restored the 

 temple of the sun-god, and states that in renewing 

 the foundations he discovered an old inscribed tablet 

 that had been placed there by Naram-Sin, thirty-two 

 hundred years before his own day, i.e., about 3750 

 B.C. The interest in archeology, therefore, is itself 

 something very ancient. 



TAIT'S LIGHT. 



Light. By P. G. Tait. Edinburgh, Adam and 

 Charles Black, 1884. 8 + 276 p. 8°. 



This book, uniform with ' Heat ' by the same 

 author, possesses in an eminent degree the 

 qualities which render all books from Pro- 

 fessor Tait eagerly welcomed by students 

 of physical science. Although written prima- 

 rily for the use of university students, it con- 

 tains much which would interest and instruct 

 one who has never pursued a definite course 

 of study in physics, while there is not a little 

 which will demand close attention from even 

 a well-equipped student. 



The first chapter gives a brief but perspic- 

 uous historical sketch of the discoveries in 

 the science of light, down to the work of 

 Alhazen. This is followed b} T chapters on the 

 sources of light, and an admirable treatment 

 of the consequences of the rectilinear propa- 

 gation of light-waves. Chapter vi. treats of 

 the speed of light. Chapters vii. to x. inclu- 

 sive are devoted to the phenomena of reflec- 

 tion and refraction. Of notable excellence in 

 the last of these, is the discussion of the rain- 

 bow and halos. 



The eleventh chapter, doubtless, contains 

 most that is novel to the general reader ; for 

 in it is an explanation of refractions in a non- 

 homogeneous medium, including as special 

 cases the phenomena of mirage. For the solu- 

 tion of the most interesting problems presented 

 b}* these frequently recurring phenomena, we 

 are indebted to Professor Tait more than to 

 any other investigator ; and probably no other 

 writer could give in such a simple form so clear 



a presentation of the subject. The last section 

 of this chapter the author devotes to a eulogy 

 on his master, Sir W. R. Hamilton, and an 

 emphatic assertion of the necessity of extended 

 mathematical study for the student of physics. 

 This concluding paragraph is as important as 

 it is characteristic in style, and may well be 

 quoted. It reads as follows : — 



" We have thought it absolutely necessary to point 

 out, even in an elementary work like this, that such 

 a perfectly general method [Hamilton's principle of 

 varying action] has been developed; but the few 

 fragmentary illustrations of it, which alone can be 

 given without the use of higher mathematics, are so 

 inadequate to the proper exhibition of its power, that 

 we do not give them here. We have said enough to 

 show that any one who wishes really to know the 

 science as it now stands must previously prepare 

 himself by properly extended mathematical study. 

 When he is possessed of this indispensable instru- 

 ment, he may boldly attack the precious stores of 

 knowledge already accumulated. There is, as yet, no 

 admission to any but those possessed of this master- 

 key." 



Fluorescence and absorption, with the at- 

 tendant phenomenon of anomalous dispersion, 

 form the subject-matter of chapter xii., which 

 contains a highly interesting extract from a 

 recent letter by Professor Stokes on the subject 

 of fluorescence. The next chapter introduces 

 the undulator}' theory of light ; the remainder 

 of the book being a development of its con- 

 sequences, including, in the final chapter (xvi.) , 

 radiation and spectrum analysis. An appendix 

 contains, 1°, Hamilton on theories of light; 

 2°, Huygens on rays ; and, 3°, the well- 

 known and astonishing letter of Laplace to 

 Young, on the undulatory theory. An index 

 closes the volume. 



Though the book is, perhaps, the most im- 

 portant acquisition to the literature of its class 

 for a number of } T ears, there is one particular 

 in which we could have looked for something 

 better. The theory of lenses given is the old 

 one, which has hardly been improved since the 

 time of Kepler, and which is repeated in all 

 English elementary works on physics. By it 

 the approximations are so very imperfect that 

 they are next to useless in practice ; while, b}^ 

 employing Gauss's improvements in the theory, 

 formulas no more complicated in form, and 

 hardly more difficult in derivation, could be 

 given, which are of the greatest utility. It has 

 long been the practice in German works, writ- 

 ten for students no more advanced than those 

 who will be the readers of this work, to give 

 the Gaussian theory ; and it is not easy to see 

 why English writers should have been so slow 

 in adopting it. 



