Although Mr. Rennie did not devote himself to the acquisition of theoretical knowledge, excepting to that general extent uhich is required by every well-informed engineer, yet he was fond of those investigations of a mixed character, where the results of experiment were combined by mathematical rules, and a train of inquiry directed and modified by the lights of theory. The wri ter of this article cannot forget the pleasure which he one day afforded to Mr. Rennie, by giving him a mi nute account of the beautiful results obtained by Con_ Lomb, respecting the resistance of fluids by his fine ap plication of the principles of Torsion Rennie has been compared with Smeaton as an en gineer; but the parallel is, in our opinion, not a cor rect one. Smcaton possessed much more theoretical knowledge than Rennie, and Rennie surpassed Smea ton in his practical resources The latter was more of a man of science ; and, if he was less of a practical en gineer, we may ascribe it, in some degree, to his having flourished at an earlier period of the arts, and at a time when the military and naval resources of our country were not called forth for its defence, and when British capital, and British enterprise, had not dared to embark themselves in works of national magnitude and inte rest.
If we could -venture, at such an early period after Mr. Rennie's death, when the adage of De mortuis ail nisi tonum is in full force, to give an opinion upon his works, we should be disposed to say, that they are sometimes characterized by a massiveness, and, conse quently, by an expense which may not have been abso lutely necessary under all the circumstances of their erection. The perfection of civil engineering must al ways be held to consist in the production of a work with the least expense of labour and materials. In looking forward to the ravages of time and of accident, there is of course no point at which we can set limits to our caution. The engineer may, with more propriety, strengthen his bridge or his aqueduct against some fu ture assault of hostile cannon, than defend them against floods that never flowed, against pressures that never pressed, or against winds that never blew. In contem plating the firmness of fresh granite, or the toughness of newly forged iron, we are apt to forget that time corrodes and disintegrates both ; and that diseases to which even their obdurate nature is subject, some times unite their strength to that of the great de strcyer. If these olvservations have any force in regard to works whose expense is defrayed out of the public treasury, their application must be still mo.e pointed
to those of a commercial character. which have been undertaken by individuals as an investment of their capital. Het° the economy of construction ought to be the principal object of the engineer, and a regard for has own reputation, and even m-ny public conside rations, ought to be kept in due subordination to that leading object.
Had it been our fortune fo he a well-employed engineer, we would have cheerfully witnessed the fai lure of some favourite erections, provided we could, at some distant period, be indulged with the sight of the remainder• balanced in skilful equilibrium, and ex hibiting their airy stability to the wonder and admiration of succeeding ages.
The caution of those engineers (atnong whom Mr. Rennie cannot be placed) who habitually shelter their scientific character under a mass of stone and iron, may be compared to the prudery of some men of science, who are exceedingly timorous of error, and who spend their lives in polishing and working up some slender, or perhaps considerable discovery. The bold and skil ful engineer, on the contrary, resembles those adven turous spirits who pant only after triumphs, and forget the slips they may have committed in securing them. The failures of the one, and the errors of the other genius, are no doubt emblazoned for a while by contem porary or local malignity ; but time refuses to collect the chaff which the breath of envy has raised, and pos terity takes cognizance only of those labours of genius which never die.
We have been led into these remarks solely with the view of explaining the grounds of the criticism which, with much hesitation, we have made on the character of some of Mr. Rennie's undertakings; but this criticism, even if it is a correct one, cannot be supposed to affect our opinion of his pre-eminent merits as a civil engi neer.
We are not aware that Mr. Rennie is the author of any memoir in the transactions of our learned socie ties.
An excellent bust of Mr. Rennie was executed in his life-time, by our great' artist Chantry, and a good medal lion by Bain has been copied from it. The late Sir Henry Raeburn also painted two excellent portraits of him. Mr. Rennie had a fine commanding figure, and was of a robust make, and greatly above the middle size. His features were strong and large, and his expression mild and agreeable.
Various biographical sketches of Mr. Rennie have appeared in our periodical works, and an eulogy upon him was written soon after his death by M. Charles Dupin.