have alluded. Many buildings, which we could particularize, used for the reception of public stores and commercial imports, now have not a cubic foot of wood in them from the foundation to the roof; so that they are in fact fire-proof, and thus afford a security unattainable by any other means. In short, iron is of all materials that perhaps to which this country is now most indebted for her prosperity, convenience, and security: it is consequently one of her most important products; and one which, notwithstanding the great improvements that an increased demand has caused in its manufacture, is probably still susceptible of a greater approach to perfection.

In order, however, that we may derive from this material all the advantages which it is calculated to bestow, we should be able to estimate its power of resistance in all the variety of circumstances under which it is likely to be introduced; to the end that we may every where so proportion all the parts, that they may be fully equal to the resistance of the strain to which we intend to expose them, without loading our supports or the fundamental parts of our machines with an unnecessary weight of material. This is a consideration which never ought to be overlooked, even in the application of timber, but. in the use of iron it is of still greater consequence from the increased specific gravity of that substance. Mere theory is not a sufficient guide in cases of this kind; and experiment, unassisted by theory, would perhaps be of still less use: - it is only by duly blending the one with the other, that we at length arrive at conclusions on which we may safely rely, and which we may advantageously introduce into practical constructions.

We called the attention of our readers to Mr. Tredgold's treatise "On the Principles of Carpentry" in the Monthly Review, vol. xcv. N. S. p. 383., where we spoke of the happy combination of theoretical and practical knowlege which the author appeared to us to possess; and the present work exhibits him in the same advantageous light. He has himself made numerous experiments, under every form that was likely to lead to practical results, and has also collected all those that have been made by others; thus forming such a mass of data as we should in vain seek in any other work: while at the same time he has founded on them a theory exceedingly simple in itself, and of the greatest utility to every one who is connected with architectural and mechanical constructions. The volume is divided into seven sections; of which the first consists of Introductory Remarks on the Use and Quality of Cast Iron, with Cautions to be observed in employing it.

Here

Here are also given two extensive tables: the first exhibiting the depth of square cast iron beams, or bars of different lengths, proper to sustain different weights from one hundred weight to five hundred tons, the beams being supported at the ends and loaded in the middle. The dimensions are so proportioned that the beam shall in no case be deflected more than one-fortieth of an inch to each foot in length. The second table shews the great weight or pressure that can be sustained by beams of cast iron, one inch in breadth, and from one inch to fourteen in depth, to several lengths from one foot to thirty feet, the beam being supported at its two ends and loaded in the middle; as also the greatest deflection of the beam in each of those instances. The former table therefore exhibits the proper working dimensions, and the latter the breaking weights, for the several cases. The object of the author in giving these tables is to save the practical builder the trouble of computation, and to prevent those errors which might arise from faults in the calculation, or from a misconception of his rules. We have little doubt that the tables will be considered as a highly acceptable present by all practical builders; particularly with the aid afforded by the second section, which is illustrative of the use of the tables, and descriptive of the method of applying them to every possible case.

In the two preceding sections, the beams are supposed to be square, or of the parallelopepid form: but it is well known that a beam is not uniformly strained in every part, and therefore that it may be reduced in size towards those parts on which the strain is the least, without in any way injuring the strength of the fabric, while a great saving may thus be made. The proper forms and rules to be observed in this reduction constitute the subject of the third section. The fourth contains a popular explanation of the strongest forms for the sections of beams, the construction of open beams, and the best form for shafts. The fifth is wholly devoted to experiments divided under the following heads, viz. On the Resistance to Flexure; Resistance to Tension; Resistance to Compression; Resistance to Twisting; and Resistance to Impulsion. We have here also, besides the author's own experiments, an account of all the most useful results that have been obtained by Reynolds, Banks, Rondelet, Barlow, Ebbels, and Rennie. In the sixth section, Mr. Tregold shews the method of applying the results obtained in the preceding section, in order to establish general rules and principles for cases in which experiments can be made only in the construction at large, resting the principles of his investigations on the following assumptions:

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The first is, That the strength of a bar or rod to resist a given strain, when drawn in the direction of its length, is directly proportional to the area of its cross section; while its elastic power remains perfect, and the direction of the force coincides with the axis.

The second is, That the extension of a bar or rod, by a force acting in the direction of its length, is directly proportional to the straining force, when the area of the section is the same; while the strain does not exceed the elastic power.

The third is, That while the force is within the elastic power of the material, bodies resist extension and compression with equal forces.

It is farther supposed that every part of the same piece of the material is of the same quality, and that there are no defects in it. If there be any material defect in a piece of cast iron, it may often be discovered, either by inspection, or by the sound the piece emits when struck; except it be air-bubbles, which cannot be known by these means.

The manner of examining the quality of a piece of cast iron has been given in the introduction; and such as will bear the test of hammering, with the same apparent degree of malleability, will be found sufficiently near of the same strength and extensibility for any practical deductions to be correct.

The truth of these premises being admitted, every rule that is herein grounded on them may be considered as firmly established as the properties of geometrical figures.'

Mr. T. then proceeds to develope his theoretical views, in the course of which he displays the great advantage that a practical engineer may derive from a well grounded know lege of the fundamental principles of mathematics. The leading analytical formulæ being established by the investigations above mentioned, they are next reduced to practical rules under several distinct heads; viz.

When beams are supported in the middle and strained at the ends, as in the beams of steam-engines.

Beams fixed at one end, as cantilivers, cranks, &c.

Beams supported at both ends, and loaded in different parts of their lengths.

Beams of pumping engines; cranks; wheels; resistance to tension; twisting, &c.; cast iron columns, pillars, or other supports, compressed or extended in the direction of their length; with various other practical applications and illustrations..

In the seventh and last section, the writer considers the effect of impulsive forces on cast iron, and its power of resistance; as for example, 1st, To determine the dimensions of a beam to resist the force of a body in motion; 2dly, To determine the dimensions of an uniform beam to resist a moving REV. APRIL, 1823.

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force;

force; 3dly, To determine the area of the middle section of a parabolic beam to resist a moving force when the breadth is uniform,' &c. &c. This section is followed by an extensive table of the properties of materials, and other data, of frequent use in calculations connected with mechanical and architectural constructions, arranged alphabetically; by means of which the rules in the body of the work may be applied to various other kinds of materials. In this table, also, we have -references to the several works from which the respective data have been obtained.

The volume is illustrated by four very neatly executed plates, each accompanied by a descriptive page, with reference to the articles which the respective figures are intended to explain. Mr. T. thus concludes his preface:

In general, it will be found that the examples are selected with a view to explain the practical application of the rules; and to make the reader aware of the limits and precautions to be attended to. In fact, the want of such information has often brought theory into discredit with some men, whereas the fault ought to have fallen on the person that misapplied it.

I hope there will be few things of any importance found in this work, for which a sufficient reason is not given; sometimes I have been compelled to omit several steps in the investigations, in order to make it as little mathematical as possible; and such omissions the reader must excuse, till a larger share of mathematical learning becomes the common lot of every practical mechanic.

The communication of any experiment, or observation, that is calculated to confirm or correct any thing I have done, I shall esteem a favor; for, should it meet with the encouragement I expect, it will soon be followed by a Second Part, on the Strength of Pipes, Mains, Tanks, Boilers, &c. ; of Chains to resist Impulsion and Pressure; of Suspension Bridges; and of Framed Work.'

We hope and trust that the author will not be disappointed in his expectation, and that the present may soon be followed by the important work here proposed; which is much wanted, and cannot proceed from a better quarter.

ART. IX. Sketch of a System of the Philosophy of the Human Mind; Part First, comprehending the Physiology of the Human Mind. By Thomas Brown, M.D. Professor of Moral Philosophy in the University of Edinburgh. 8vo. 8s. Boards. Longman and Co.

ART. X. Lectures on the Philosophy of the Human Mind. By the late Thomas Brown, M. D., &c. 8vo. 4 Vols. 21. 12s. 6d. Boards. Longman and Co.

THE

HE acuteness and analytic spirit of the late amiable Professor Brown were early in life made known to the world by his strictures on Darwin, and by his profound Essay on

the

the Relation of Cause and Effect. The Sketch' now before us is a fragment printed by him when in a declining state of health, as a text-book for the students attending his class; and the 'Lectures' are a posthumous publication. All these productions exhibit the same characters of mind, viz. great freedom of inquiry, patience of research, and subtilty of investigation, joined to a humble consciousness of the limited sphere of the human faculties, and to a lively sense of the. omnipresence of a superintending Providence. Considering how much the mind of man is liable to be warped by established predilections, and how much habits of controversy tend to impart tenacity to favorite opinions, it is in no slight degree creditable to Dr. Brown that he generally places the arguments of his opponents in the clearest point of view, and waives all minor and technical objections in order to meet the very thing signified.

The Sketch is imperfect even as it relates to the physiology. of the human mind: but, as far as it goes, (and it comprehends only what Dr. Brown designates the external affections of the mind, and that branch of the internal affections which he terms intellectual states,) it is an excellent compendium. Indeed, to those who wish to see the author's doctrine in a compact and succinct form, it may be recommended for perusal in preference to the portion of the Lectures in which the same subjects are developed and discussed at large: for, in the Lectures themselves, the attention of a reader is often only distracted by episodes, and interludes of quotations from poets and from writers of humour; which, however, it may have been desirable or even necessary to introduce for the diversion of a youthful audience, and to attract any share of their regard to the intricate subjects discussed by the Professor. These quotations are also in general extremely apt, and illustrative of the subject treated: but the greater number of them are familiar to persons of any reading; and some would, naturally recur to their recollection even without any reference being made to them.

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In the early part of the Lectures, Dr. Brown explains the physiology of the human mind, and in the latter part proceeds to consider the duties of man as a moral being. cording to the Doctor's view, the object of natural philosophy is to ascertain the different successions of physical phænomena, while that of moral philosophy is to ascertain the different successions of the phænomena of mind. These latter he arranges in two classes; viz. first, its external, and secondly its internal affections. The external affections he subdivides according to the senses through the medium of which the sug

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gestion