July 25, 1884.] 



SCIENCE. 



87 



The classification adopted is at some points 

 radically different from that employed in the 

 first edition, particular!}' as regards the prima- 

 ry divisions of the class. The number of ' or- 

 ders ' now adopted for North-American birds, 

 which belong all to the ' sub-class ' Carinatae, 

 is thirteen, subdivided into twenty sub-orders, 

 sixty-three families, and seventy-seven sub- 

 families. 



The twelve years which have passed since 

 the appearance of the original edition of the 

 ' Key,' have been marked by a striking increase 

 in our knowledge of North-American birds. 

 This advance would alone render any general 

 work on the subject, published at that date, to 

 some extent antiquated and unsatisfactory, 

 however excellent it may have been in its time. 

 The old ' Key ' has unquestionably had a career 

 of usefulness, and has helped on the advance 

 that has so strongly characterized the last dec- 

 ade of North- American ornithology ; the ob- 

 ject of the treatise being to enable any one, by 

 its aid, to identify his specimens without re- 

 course to other information than that the book 

 itself afforded. The undertaking was to some 

 extent, at least in its methods, an innovation 

 in zoology, and, however well it may have 

 served its purpose, was obviously open to im- 

 provement, as such attempts must always be. 

 Its defects were doubtless as quickly seen by 

 its author as by others ; and to remedy these, 

 and bring the work down to date, the author 

 was led to prepare this much enlarged, and in 

 many ways greatly improved, second edition. 

 The first edition emphasized, and in a large 

 degree initiated, a new departure in respect to 

 the status of many forms of North- American 

 birds, which were degraded from species in reg- 

 ular standing to the grade sub-species or geo- 

 graphical races, and referred, as l varieties,' to 

 the species from which they were found to be 

 not completely differentiated. Since that time 

 the custom has arisen and become established, 

 among American ornithologists, of discarding 

 the interpolated ' var. ' between the varietal and 

 specific names of such forms ; and, in accord- 

 ance with this custom, the new ' Key ' adopts 

 the new - trinomial ' nomenclature for such in- 

 tergrading forms as it seems wise to recognize 

 in nomenclature. The names are, in fact, 

 strictly those of the author's revised ' Check- 

 list,' published in 1882, plus about a dozen 

 since added. 



As regards paper and typographical execu- 

 tion, the work is all that need be desired ; the 

 composition and press-work being that of the 

 Cambridge University press. The author tells 

 us that his publishers generously allowed him 



' to make the book to suit himself,' sparing no 

 expense to which they might in consequence 

 be put. While some of the cuts are not above 

 criticism, many of them are fine, so that their 

 average grade is high ; and in nearly every 

 case their origin is duly accredited. The work 

 as a whole is certainly very tastefully executed. 



WIEDEMANN'S ELECTRICITY. 



Die lehre von der elektricitclt. Von Gustav Wiede- 

 mann. 2 vols. Braunschweig, Vieweg, 1882-83. 

 11 + 795, 7+1002 p. 8°. 



The work which forms the subject of this 

 notice is the successor to ' Die lehre vom 

 galvanismus und elektromagnetismus," by the 

 same author, first published in 1861, -and fol- 

 lowed by a second edition in 1874. Ever since 

 its publication, the original work has been 

 recognized as a practical!}* exhaustive treatise 

 on the topics included within the limits set by 

 the author. Every discover}* and observation 

 is referred to the original publication, and its 

 date is given. These references, so charac- 

 teristic of the previous work, are continued 

 and extended in the present treatise ; and 

 they form a classified index to the literature 

 of electricity with the historical advantage of 

 dates. One is surprised at the extent and 

 range of the literature to which reference is 

 made. 



It is a suggestive fact, that a third edition 

 simply of the original work could not repre- 

 sent the present knowledge of galvanic elec- 

 tricity and electromagnetism with that unity 

 and completeness which the author's plan con- 

 templated. The separation between static and 

 galvanic electricity, which obtained up to the 

 middle of the present century, can no longer 

 be maintained : hence Professor Wiedemann 

 wisely decided to extend the scope of his work, 

 and to prepare with immense labor a practically 

 new book under the more comprehensive title 

 of -Electricity.' This decision must be uni- 

 versally approved ; for, aside from the very 

 evident advantage of having a complete trea- 

 tise in place of a partial one, the present con- 

 ception of electricity forbids the treatment of 

 the subject under its historical divisions. This 

 division, which seemed imperative twenty-five 

 or thirty years ago, has now become impossi- 

 ble. No fundamental differences between the 

 two classes of electricity, due to different 

 methods of generation, are now recognized. 

 With galvanometers sufficiently sensitive to be 

 affected by static discharges, on the one hand, 

 and with electrometers capable of measuring 



