a<8 



THE CIVIL P:NGINEER ANi> AKCHITECT'S JOURNAL. 



I AudOBT 



inadvertently mistook the purport of one of Dr. (Gregory's sen- 

 tences, and though what we said was true, omitting the word 

 which Mr. Law forces upon us. Or. (iref^oiy's sc^iitence emVA that 

 word is perfectly correct also. Mr. Law unnecessarily injures his 

 case hy a <|uotation from Dr. Whewell, which has not the remotest 

 connection with the suhject. Dr. Whewell speaks of accelerated 

 velocities in tlie several bodies: Kmerson and (Jrefjory, <pf uniform 

 velocities only. The law stated hy the two latter depends for its 

 proof on wholly different principles to that enunciated hy the 

 former. The connection between them wliich Mi-. Law attempts 

 to establish, is of that kind whicli exists between the 1st of 

 March and the foot of Londoii-hridffe. We have not the slightest 

 objection to let the whole dispute between us and our correspon- 

 dent rest on tlie reply ufdiiij real mathematician to this (pjestion : — 

 Does not this attemi)t to confound two principles essentially 

 different display either the most profound ignorance or the most 

 hopeless confusion of thought respecting the science of exact 

 mechanics? If Mr. Law can get ojic competent umpire to answer 

 that question in his favour, we will give up the wh(de controversy. 



The idea respecting the natural .s/opn has the merit of originality. 

 Mr. Law •■ prefers" giving it a meaning which it has not hitlierto 

 received. He says, the natural sh)pe is the slope along which rup- 

 ture would take place if the revetement wall were removed. Now, 

 the definition of natural slope, as ordinarily used, is that it is the 

 very slope along which rupture cannot take place — its friction being 

 just capable of sustaining the superincumbent mass without the 

 assistance of the wall. 



We are next said to have misunderstood Dr. Gregory respecting 

 the conditions on which he discusses one of the cases of the equi- 

 librium of arches. This is mere assertion. We repeat the coun- 

 ter-assertion, that in the case referred to, conditions are assumed 

 which, (|uite independently of all statical considerations, render it 

 impossible that the arch from its mere form could he overturned. 

 Mr. Law says that " no such conditions are assumed, or indeed 

 necessary." Not necessary, indeed ! Why, they make Gregory's 

 lucubrations nonsense. Does Mr. Law mean to infer, that sometimes 

 it is necessary that Gregory should talk nonsense ? 



Then follows an accusation against us, of having maliciously 

 misquoted and j)erverted the words of the book under review. 

 The best answer to personality is silence. 



With regard to the '• careful and often-repeated experiments" 

 whicli Mr. Law asserts to have been repeatedly made, we have 

 already explained, as clearly as vve could, the confusion here made 

 between mechanical experiment and pure geometrical measure- 

 ment of distances. Tlie words, " uniformly retarding force," 

 involve the very conclusion which is declared to be the result of 

 numerous trials ; just in the same way that the first proposition in 

 Euclid is a pure deduction from his definitions. Experiment wouMi 

 be as preposterous in the one case as the other. 



The following quotations, the former from Moseley's Principles 

 of Engineering, the latter translated literally from Poisson's 

 Traite de Me'caniipie, are offered in a faint hope of clearing Mr. 

 Law's ideas respecting the resistance of inertia : — 



" So many ililIiuMJUes, hoHcver, opposi; Ihcinselvis lu the iutroiiuclion 

 of the leim vis uurtite, associated wuli llic deliiiilive idea of au opposiiip; 

 force, inlo llif iliscussion of (incsllons of niecliaiiics, that il lias iipjieand 

 to the amiiorof this work desirable to avoid it."— I'liiiciples of lingiueeriui;, 

 page vill. 



"It is iniporlaiit to reclify an inoxnct I'xprcssion, « iiich is ofien em- 

 ployed and li-iids Id a coiifiisiuii of ideas. Iiiia};uie tliat a body i; placed 

 on a liorizoiilai plane, and that it is not retained liy any friction. If 1 wish 

 to make il slide on this plane, it is nevertheless necessury, on aeconnt of 

 the inertia of the matier, that I exert some eflorl ; if to this body he added 

 a second, then a Ihird, &c., it is necessary ihat 1 employ, to produce the 

 same degree (if motion, a force more and more eiinsirlerable. 1 thall in 

 eacii case experience a sensalion of the (Hon which I shall he obliged lo 

 exert; hut I must not llience conclude that the m.ilter opposes any resist- 

 ance to ihis elfirt, iiiic! Hint there exists ill the bodies what is veryimpro 

 perly termed risistiincc nf ineilia. When any one expresses himself in this 

 manner, he cimlounds the sensation wl.ieli he has experienced, and which 

 results Iroiii the ellcirl which he has made, willi ilie sensation of a resist- 

 ance which does nut exist."— Traite lie Mecniiiipie, No. 120. 



Respecting the problem of the weight oscillating at the ex- 

 tremity <if a flexible string, Mr. Law himself shall be umpire, if he 

 will ])romise to make the following experiment ;— Let the oscillating 

 weight descend a vertical distance of one foot, and let the peg 

 interfere with the string at a distance of one inch from the weight. 

 If, then, he find the string so accommodating ;is to stretch itself 

 out the odd eleven inches, necessary to permit the weight to rise 

 to the former height, we will acknowledge ourselves beaten. 



The propositions printed side hy side after the next paragraph, 

 amount to this : If a body he in one place, quoth Emerson, it ought 

 to be somewhere else. To which Dr. Gregory responds, Amen. 



From the manner in which Mr. Law meets our criticism upon 

 his author's erroneous definition of centrifugal forces we infer 

 that he finds there is no tenable defence. He also candidly acknow- 

 ledges two other mistakes, and therefore we have nothing further 

 to say of them. Our remark on the equality of the total forces of 

 compression and tension in a beam, were manifestly restricted to 

 the particular case under examination — that where there are not 

 appreciable horizontal forces .-icting externally (ui the beam. 



It is important lo observe, that throughout Mr. Law's letter he 

 never discusses any question on il.s own merits. He contents him- 

 self with apjiealing to authorities. This course is at least dexterous 

 fur with the unlearned an array of imposing names is but too apt 

 to carry conviction. The authorities quoted are, however easily 

 disposed of: several of them are of little weight when opposed 

 as we have shown them in several instances to be, to the most pro- 

 found continental writers. The re.st of the citations are either 

 irrelevant, or make directly against Mr. Law's tenets. Had he 

 suffered the contrtnersy to rest on its own abstract merits our 

 task would have been more easy to ourselves, and more satisfac- 

 tory to the cause of truth. It would be an insult to his under- 

 standing, to suppose that he did not perceive that many of the 

 errors which he defends hy quotations w ere, in reality, indefensible 

 in any other way. Casuistry and perverse ingenuity, however well 

 suited for mere disputation, are never the weapons of a man of 

 science. 



Mr. Law seems very fond of appealing to Woolwich Pro- 

 fessors. Why did he not <piote Mr. Davies or Mr. Rutherford- 

 gentlemen who have acquired for themselves reputations not con- 

 fined to the regions of Woolwich.? It is veiy unfortunate, that 

 the only two works written by Woolwich mathematicians which 

 we have lately had to review, have been anything but very credit- 

 able to the scientific character of that institution ; and this is the 

 niore to be regretted, since, as we have already hinted, inaccuracy 

 in conceiving physical ideas, and clumsiness in developing them 

 analytically, are not common to all the Professors — at least to all 

 the Teachers — of the Royal Academy. 



SANITARY LAWS AT HOME AND ABROAD. 



The most destructive scourges of the human race are the epi- 

 demics and contagious diseases produced by a polluted atmosphere, 

 and the congregation of men in crowded cities. Famine and the 

 sword slay their thousands — the pestilence that walketh at noon- 

 day and in darkness its tens of thousands. The ravages of war 

 and want are, partially at least, within human control; but when 

 the de.stroying angel comes, borne on the breath of " quick pes- 

 tilence," human skill and energy are all but powerless against 

 him This sudden destruction, moreover, is not all that is caused 

 by the infected air and artificial habits of populous places. The 

 maladies indirectly induced, the remote consequences of a morbid 

 habit of body which renders it a kindly soil for the future seeds 

 of death, the degeneracy of sickly offspring who reap in a later 

 generation the bitter fruit sown by their parents — these are among 

 the penalties which the denizens of large towns too often pay for 

 inhaling the hot vapours of the foundry or furnace, or breathing 

 the stagnant air of crowded courts and lanes, where overhanging 

 house tops shut out the pure breath of heaven. 



Prevention is almost the sole defence against these evils; for 

 when once dcveloiied, they :ire either too sudden or too deeply 

 rooted to :idmit of effectual remedy. A curious chapter in the 

 history of the internal economy of states is that which the various 

 sanitary provisions adopted uniler different forms of government. 

 Nations working for the same end, the public health, seek it by en- 

 tirely different means. On the ('oiitiuent, where the rights and 

 liberties of individuals seldom constitute a serious obstacle to State 

 purposes, the most stringent sanitary regulations have long existed 

 and the surveilhince of jiolice, which is almost unknown in Eng- 

 land, constitutes the principal means of effecting them. Here, 

 the public jealousy of state iiiterference, and a sensative regard 

 for the rights of property, have long prevented the institution of 

 a general organised .sanitary system. The Public Health Act, 

 which will soim he the law of the land, makes the first provision 

 for such a system in Englaml ; and it becomes, therefore, interesting 

 to compare it with the machinery adopted for the same purpose by 

 our continental neighbours. 



The Public Health Act comprises two part.s, the construction of 

 n. new Central Board of Health to put it in motion, and of Aoca/ 

 Boards, for the purpose of carrying its details into effect. As the 



