March 3, 1882.] 



KNOWLEDGE • 



377 



3Rffaifh)S. 



ELECTRICITY AND MAGNETISM.* 



A DEBT of gratitude is due to writers like Professor 

 Tliompson, who, being thoroughly mastci-s of tlieir 

 subject, present, not their knowledge, but what the student 

 wants to know of tlie subject, in clear and simple terms. 

 The present Iwok is a capital specimen of the sound popu- 

 lar science-treatise. It is clear, compact, and correct It 

 does not wander ofl" into disquisitions aV)0ut a multitude 

 of matters too profound to be of interest to the learner ; 

 but every chapter, in every section, in every sentence, goes 

 straight to business. The theory of electricity adopted by 

 Professor Thompson is that electricity, whatever its true 

 nature, is one not two, and that this electricity, whatever 

 it may prove to be, is not matter and is not fnerriy, 

 but resembles both in one respect, that it can neither 

 be created nor destroyed. The question whether 

 positive electrification or negative electrification be 

 the state in which thei-c is more electricity than 

 in the surrounding space is not decided, but Professor 

 Thompson inclines to the belief that negative electrifica- 

 tion is really the state of excess. The fact that the rate of 

 dissipation of charge is greater for negative than for 

 positive electrification seems certainly to point this way, 

 for the law of the loss of charge is precisely the counterpart 

 of the law of loss of heat, and it is well known that for 

 e(|ual differences of temperature between a body and its 

 surroundings, the rate of loss of heat is greater at a higher 

 tfuiperature than at a lower, i.e., the body that is really 

 hotter loses its heat fastest 



The " Lesson on Terrestrial Magnetism " is one of the 

 most interesting in the book. The statement that the north 

 magnetic pole is in a particular latitude and longitude, ought, 

 perhaps, to be modified, so as to indicate the probability, 

 or rather the certainty, that the magnetic pole changes 

 with the magnetic meridians. But this comes out clearly 

 enough from other statements. The book is well illus- 

 trated and carefully printed. Wherever formulas occur, 

 they are correctly given ; this, in fact, is a characteristic of 

 all works published by Messrs. MacmiUan. 



SPELLING AND PUNCTUATION.t 



Every author and intending author, many students, and 

 all printers, may study this little treatise with advantage 

 and interest It is also worth reading by those before 

 whom the work of authors and compositors is presented 

 in the form of printed books. " Literary men," says the 

 late Mr. Beadnell, in the preface, "seldom pay much atten- 

 tion to such matters as punctuation and syllabication, often 

 little to spelling (I) ; trusting to the printer, or rather his 

 readers, to correct the errors and supply the deficiencies of 

 their manuscripts." They ought not to do so, at least as 

 regards punctuation ; for the man who has thought out a 

 subject should know better what he means to say about it 

 than the compositor, who has simply to set up the author's 

 words, and incorrect or defective punctuation often plays 

 the mischief with the ideas which an author intends to 

 present Unfortunately, writers who are careless in this 

 respect, injure those who punctuate for themselves. 

 Printers have naturally learned to believe that an author, 



* " Elementary Lessons in Electricity and Magnetism." By 

 Sylvanus P. Thompson, Professor of Experimental Physics in 

 Vniversity College, Bristol. (London : Macmillan & Co.) 



+ " Spelling and Punctuation : " A Manual for Authors, Students, 

 and Printers. By Henry Beadnell. (Wyman & Sons, London.) 



like Artemus Ward's " literary cuss," " can't punctooate 

 wutli a cent '' ; so they punctuate for him, even when he has 

 most carefully attended to the matter. He writes, let us 

 say, " Rocks which are covered witli seaweed are to some 

 degree protected from the sun's heat," and by putting a 

 comma after the words rocks and seaweed, they make him 

 lay down two general propositions — very far from his real 

 meaning — these, namely, that rocks are, as a general 

 rule (1), coveretl with seaweed, and (2), to some degree 

 protected from the sun's heat. So that, because many 

 writers are too lazy to punctuate pioperly, the careful 

 writer has to watch lest his meaning should be perverted 

 by incorrect or concealed by e.xcessivc punctuation. Mr. 

 Beadnell gives a very logical account of the comma, colon, 

 semicolon, parenthesis, dash, kc. ; it may l)e doubted, how- 

 ever, whether a little common sense is not better than the 

 laws of logic, as a guide in this matter. In one or two 

 places it has led our author astray. Thus, he says that 

 where the subject of an affirmation has certain words 

 attached to it which constitute the predicate and comple- 

 ment of the proposition, and are not (as they at first sight 

 look) a thought interposed between the subject and the 

 predicate, there must be no comma after the subject, giving 

 as an example this sentence : — 



The French demurring to the conditions which the English com- 

 mander ofifered, again commenced the action. 



Here, he says, the Frenchmen's demurring to the con- 

 ditions is not mentioned incidentally, as a parenthetical 

 explanation, but is the principal proposition of the sentence 

 upon w^hich the next proposition depends. And then he 

 gives, as a somewhat different example, to render the 

 matter clearer, this : — 



The French having occupied Portugal, a British squadron, under 

 Rear-Admiral Sir Samuel Hood, sailed for Madeira." 



But the two cases are not only different, they are diverse. 

 In the first sentence the punctuation is clearly wrong, in 

 the second it is clearly right. The first is really equivalent 

 to this : " As the French demurred to the conditions which 

 the English commander offered, again commenced the 

 action," which is absurd ; a comma after " French " put.*; 

 the sentence right On the other hand, a comma after 

 "French" in the second sentence makes it wrong and 

 absurd (logically, it could then only bear the interpretation 

 that Portugal is a British squadron under Rear-Admiral Sir 

 Samuel Hood, which the French occupied, and then sailed 

 for Madeira). The proper way of treating the first sentence, 

 in order to show the importance of the words " demurring 

 to," itc, is to do what Macaulay used to do u\ such cases 

 (and very often when it was not wanted), to make two 

 distinct sentences, thus : — 



" The French demurred to the conditions," Ac. " They aprain 

 commenced the action." 



GEOMETRICAL EXERCISES FOR BEGINNERS.* 



These exercises are intended to assist the young student 

 of geometry to understand those propositions with which 

 he has later to become familiar. They will be liked by 

 lovers of old Euclid, as they deal more with ancient than 

 modern geometry, and adopt the ancient methods of pre 

 senting geometrical truths. In some respects we are glad 

 to see this, in others tlic ancient methotls are not so well. 

 We believe few things in Euclid, for instance, serve more 

 to repel beginners than the general form m which the 

 enunciations are presented. Not only — which is some- 

 thing — is a good deal of space wasted, but — which is 



• " Geometrical Exercises for Beginners." By Samuel ConstaWf, 

 Trinity College, Dnblio. 



