16 



SCIENCE. 



[Vol. II., No. 22. 



and from Dunkirk to Ostend. Tbe Bnixelliau 

 and Laekenian s_ystems form superficial hills in 

 the neighborhood of Brussels, Gand, etc. The 

 olio'ocene sj-stem shows two principal divisions 

 (tongrian, rupelian), which stretch across the 

 lower part of the ri\'er Escaut, where it leaves 

 the eocene districts, through which it tlows 

 in the western part of the countrj*. The plio- 

 cene formations overlap irregularlj- the under- 

 lying tertiarj- beds, and extend from Antwerp 

 to Lou vain. Manj- fine fossils have been found 

 in these beds, where Mourlon admits several 

 divisions, — Dicstien (in part) , Anversien, and 

 Scaldisien. The last chapters of the work 

 treat of the quaternary (diluvien, hesbayen, 

 and campinieu) and recent periods. 



Though special attention has here been 

 given to the stratigraphical extent and dis- 

 position of the beds, the author has treated 

 with equal care of their lithological and paleon- 

 tolog'ical characters, their minerals and fossils, 

 and the useful products thej' furnish to Bel- 

 gian industrjf. It will be enough, to indicate 

 what amount of documents are included in the 

 book, to state that the lists of fossils occupy 

 240, and the bibliographical lists 144 pages. 



DU MONCEL'S ELECTRO-MAGNETS. 



Electro-magnets. The determination of the elements of 

 their construction. By Th. Du Moncel. From 

 the second French edition. New York, Van 

 Nustrand, 1883. 



The same. Translated from the French by C. J. 

 Wharton. London, Spon, 1883. 



The great interest in the practical applica- 

 tions of electricitj' demands simple treatises on 

 the most economical methods of making elec- 

 tro-magnets. ' Count Th. Du Moncel has en- 

 deavored to supply this want, and has added 

 another treatise to the long list he has already 

 pubhshed upon electricity. He disclaims any 

 endeavor to make a treatise on electro-mag- 

 nets which shall embodj' scientific theories 

 upon that most difficult of subjects, theoretical 

 magnetism. His desire is to give the mech- 

 aniciau a vade mecum bj' means of which he 

 can construct electro-magnets for operations 

 outside the laboratory. Indeed, this treatise is 

 intended to stand in the same relation to the 

 maker of dj'namo-electric machines as a trea- 

 tise on the practical construction of boilers, 

 minus theories of elasticity, would stand to 

 the constructor of steam-engines. There is 

 need for such a treatise, undoubtedly ; for 

 much expense can be saved bj- a little knowl- 

 edge whei'e to put the material to the best 

 advantage. Most of the dynamo machines 



which are before the world at the present time 

 are defective in the arrangement of the wire 

 of the field electro-magnets. Does the trea- 

 tise of Du Moncel suppl}' this want? The 

 author follows the antiquated French fashion 

 of expressing the resistance of a wire in 

 terms of the length and diameter, without 

 specifying, in many cases, the specific resist- 

 ance. Thus, instead of ohms, we read so 

 many metres of telegraiih-wire ; and one must 

 enter into a troublesome arithmetical drudgery 

 to ascertain what is meant. The English edi- 

 tion, published bj- Spon, states in the preface 

 the relation between Du Moucel's units and the 

 commonlj- received units of resistance and 

 electro-motive force ; but the American edi- 

 tion, published b3f Van Nostrand, leaves the 

 reader to find out this relation after he has 

 plodded some distance through the treatise. 



The two imprints, one b}- Spon and the 

 other bj' Van Nostrand, are carelessly edited. 

 Thus, on p. 43 in Van Nostrand, we find aa 

 inconsistencj' between the values of t- and A, 



On p. 47, Van Nostrand gives 



16 ^ypy^ 



ab = -S 0.000506 

 e- 



= 5 ( 0.0225 ^V^^); 



while Spon gives, on p. 34, 



ab 



.0225 



= h .000506 o 



We give this as an example of similar mis- 

 takes which meet the eye. The question 

 arises whether a more carefully prepared 

 treatise, which would start with the funda- 

 mental sj'stera of electrical measurements, is 

 not still needed. It is useless for an}- one to- 

 endeavor to become a practical electrician 

 to-daj-, without a sound training in mathe- 

 matics as far as the principles of tlie differ- 

 ential and integral calculus. A genius may 

 arise, but he will know enough to emploj- a 

 steadj' plodder who has been steeped in the 

 IDrinciples of the calculus. Most constructors 

 who desire to build electro-magnets will find 

 that the exigences of space and material will 

 demand a certain form. Unless they under- 

 stand the theorj- of magnetic measurements, 

 they will find the treatise of Du Moncel of" 

 little value ; for so ma.ny and so large approx- 

 imations must be made, that the final result, 

 would not differ much from those obtained by 

 a thumb-rule. We commend to the practical. 



