June 5. 1879] 



NATURE 



119 



There appear to be several discrepancies between the 

 earlier and the later parts of the book. On p. 178 men- 

 tion is made of " a battery known as the Pile Marie 

 Davy," in which sulphate of mercury is used ; and which 

 is stated to be weaker than Daniell's cell, but to have been 

 used to some extent in France. On p. 434 appears an 

 account of the " Afarii-Davy Battery " which " has been 

 much used in England, and is largely employed in France 

 and on the Continent." It is twice stated to contain bistcl- 

 phide of mercury J and lower down on the same page it is 

 declared on the authority of Latimer Clark to have an 

 electromotive force of 76, as compared with 56 for a 

 Daniell's cell. 



The divided ring electrometer of Sir W. Thomson is 

 described on p. 79. Another description and a figure of 

 the instrument are given on p. 529. The quadrant elec- 

 trometer, of which there is no mention in the early 

 chapter where Peltier's and other electrometers are given, 

 is described at some length and figured on p. 537. 



In a couple of pages devoted to the " Insufficiency of 

 the Contact Theory " of voltaic electricity, the authorities 

 cited are Faraday, Roget, and "lastly," Sir W. Snow 

 Harris ; the later fundamentally important researches of 

 Hankel, Thomson, Kohlrausch, and Clifton, being abso- 

 lutely ignored. 



Two pages (22 and 23) are devoted to Varley's multi- 

 plier, but there is not a word about the earlier invention 

 of Nicholson, nor the more recent "replenisher" of Sir 

 W. Thomson. Nor is there a single word about the Holtz 

 machine. 



In magnetism there is no attempt to explain the mean- 

 ing of the term "declination," and the word " variation " 

 is made to do duty both for declination and for the varia- 

 tion of declination, in a manner most perplexing to the 

 uninitiated in electrical terms. And yet the book is 

 avowedly "written under the idea" that the student 

 "approaches the subject from the datum line of ignor- 

 ance ! " 



We cannot accept without protest the following state- 

 ment : — 



" The fall of tension is always accompanied by its con- 

 version into heat "(p. 198). Nor this : "With sulphuric 

 acid the ions {sic) are H and SO4 (Sulphionide of 

 Hydrogen)." 



The term the "absolute quantity of electric force in 



matter^'' used on p. 223, is open to serious objection. On 



p. 209 we read that "the common non-absolute unit of 



, work involving the product of a weight into a length is 



styled kilogiamme, or foot-pound." 



. The following statement :—" we have, calling C the 

 charge, Q the quantity, and i" the siu-face, C= ^," ap- 



, pears on p. 6r. After pondering over this formula, we 



I give it up. 



We are compelled to take exception to the following 

 manner of stating the well-known law of Ohm:— "Thus 

 let F denote the actual force of the current, that is, its 



: power to produce heat, magnetism, chemical action, or 



\ any of its other effects; E the electromotive force, and R 



' the resistance of the wires and liquids, then F= — » , 



I99)- To say nothing of the assumption that all the 

 "effects" of the current are simply proportional to the 



current strength, we protest against the introduction of 

 that much-abused word, force, where every other treatise 

 on electricity in the language has put "strength" of 

 current or "quantity" of current or "intensity" of cur- 

 rent. On p. 209 the formula again appears, this time as 



C =-„) which is the form adopted by Maxwell, Jenkin, 



CuUey, Foster, Chrystal, the British Association Commit- 

 tee, and in the well-known treatises of Ganot and Des- 



r j-i 



chanel. Guthrie uses (2 = „, and the form / = - is 



used by Maxwell, Gumming, Clark and Sabine, Verdet 

 Daguin, Wiedemann, Jamin, and continental writers 

 generally. It is very desirable that needless departures 

 from one or other of the established forms should be dis- 

 couraged. The " Return Charge " of the Leyden jar, so- 

 called on p. 46, is now almost universally denominated 

 the "residual'' charge, a term which is far preferable, as 

 it cannot be confounded with the return shock or rettirn 

 stroke, or " back stroke," as it is termed on p. 91. 



In the chapter on the telephone occurs the following 

 passage :— " In 1874 Mr. Elisha Gray, of Chicago, Ame- 

 rica, succeeded in effecting the transmission, through a 

 wire, by means of electricity, of the variable intensitv as 

 well as the pitch of a sound. Subsequently he invented 

 a form of telephone by which all the three characteristics 

 of sound could be transmitted. As a result, the electri- 

 cal transmission of articulate speech became an accom- 

 plished fact. It remained, however, for Prof. Graham 

 Bell, of the Boston University, to accomplish this latter 

 feat in the most effective manner." Do we understand 

 Mr. Preece to endorse Elisha Gray's claims to precede 

 Bell as the inventor of an articulatitig telephone 1 As a 

 minor blemish, we notice the name of Philip Reis ap- 

 pears as Reiss. Many persons confound the inventor of 

 the original singing telephone with Peter Riess the author 

 of the Reibuiigselcctricitdt ; and the misspelling of his 

 name helps to perpetuate the error. One other quotation 

 from the editorial add tions is not devoid of interest : 



"The subdivision of the (electric) hght has recently 

 occupied the attention of inventors. Jablochkoff works 

 four lamps simultaneously. Wallace has worked ten. 

 Attempts have been made to do this on a much larger 

 scale by raising platinum and iridium to incandescence, 

 or to that temperature just below melting-point. A soft 

 and gentle light is thus obtained. But the result has not 

 been commercially successful, though probably this is the 

 direction in which ultimate success will be obtained" 

 (p. 576). 



We wish heartily that the editor of this new edition 

 had himself re-written the work ; a reviewer's task would 

 then have been much more agreeable. 



SiLVANUs P. Thompson 



LENZ'S SKETCHES FROM WEST AFRICA 

 Skizzen aus Westafrika. Selbsterlebnisse von Dr. Oscar 



Lenz. (Berlin: Hofmann and Co., 1878.) 

 Tr\R. LENZ'S "Sketches from Western Africa" are 

 ■L^ unusually interesting and instructive. They are 

 not descriptions of travel in the ordinary sense of the 

 word, but form a collection of essays, perfectly inde- 

 pendent of each other, describing in a masterly manner 

 the natural and social conditions of that scantily investi- 

 gated coast, as they presented themselves to the eminent 



