ISiB."] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



323 



nities which it formerly received from the Italian school and its 

 followers. Opposite as they are in their tastes, all these parties 

 are alike in one respect, they heing all alike one-sided, prejudiced, 

 and intolerant in their antipathies, and cheating themselves out 

 of much varied enjoyment hy liniitinj; the sphere of it to the 

 compass of a single style of the art ; instead of sympathising with 

 the beautiful and intrinsically aesthetic in architecture, whatever 

 may be the particular form under which it presents itself, or the 

 name to which it answers. 



STUDY OF MECHANICS.* 



Mechanical science is certainly the most ancient branch of 

 natural philosophy. The very commencement of existence is the 

 exercise of force ; and of all his physical powers, the first which 

 man puts into operation is his strength : the whole business of his 

 animal life consists in the exercise of it, and from the beginning of 

 the world until now, every human being, from his cradle to his 

 grave, has been making repeated experiments in that knowledge 

 which only modern philosophers profess to teach with perfect 

 accuracy. 



Why has a study, of which the study has been universal and 

 uninterrupted, advanced with such slow and uncertain steps? 

 This tardy development is not the history of all other sciences. 

 Geometry — the exact knowledge of forms and dimensions — though 

 its applications to the purposes of life are much fewer, and much 

 later required, became a methodic science, while mechanics still 

 remained a crude collection of facts. So late as the end of the 

 sixteenth century, the very simplest phenomena of falling bodies 

 were in doubt. A heavy body falls to the ground more rapidly than 

 8 light body, said the opponents of Galileo. — The weight of the 

 bodies makes no difference in their motion, was his counter-asser- 

 tion. Now, here was a question which the world might be presumed 

 to have settled for itself before it was five thousand six hundred 

 years old. If there be any operation of nature more frequently 

 observed than another, it is this very one of the descent to the 

 ground of unsupported bodies. Yet, notwithstanding the incal- 

 culable number of previous observations, it was necessary that 

 Galileo should appeal to direct experiment to support his views. 

 He ascended to the top of the leaning tower of Pisa, with two 

 balls differing very much in weight, yet both of such a density as 

 not to be much affected by the action of the air. The balls were 

 simultaneously dismissed from his hands, and reached the ground 

 at the same moment, or at least %vithout perceptible interval. 



This was conclusive .'—On the contrary, the discussion gained 

 in vehemence what it lost in argumentative reasoning. Galileo's 

 opponents were not convinced, but merely irritated. From time 

 immemorial, it had been believed that the greater the mass of a 

 body, the greater was the acceleration of gravity. Was it to be 

 supposed— they asked— that they and all preceding philosophers, 

 from the time of Aristotle, had been mistaken on this fundamental 

 point ? Rather than concede that, they chose to disbelieve the 

 evidence of their own senses. 



The momentum of mind operates as manifestly as that of 

 matter. The difficulty which Galileo had to combat, arose not 

 from the nature of his subject, but from the necessity of overcoming 

 the previous tendency of men's minds, and moving them in a 

 contrary direction. This difficulty has existed throughout the 

 history of mechanical science : now, also, it is the greatest obstacle 

 to the student's progress. 



If there were no previous errors and prejudices to be overcome, 

 no previous misconceptions to be unlearned, mechanics would be 

 one of the most easily-acquired branches of human knowledge. If 

 the brain were as an unwritten, unsullied scroll, ready to receive 

 those fair characters which have been traced and perfected by the 

 co-operation of the most stupendous efforts of human intellect— 

 the liability to error and confusion would almost cease to exist, 

 liut this can never be the case. The student has been learning 

 mechanics long before he commenced the study of its systematic 

 laws. He has, as was before said, been experimenting on the 

 subject from his infancy ; and his experiments have been so crude 

 and irregular, that almost every conclusion derived from them 

 involves a certain amount of error. 



Not until a very considerable progress be made in the study of 



tecf?cru™.^f"M°''r"°" '° ^"r ';:,J'"' P,"'"""'", of the "Civil Engineer andAr^i- 

 Cox B.A M'cbaniLS, applicable to Slruclures and Machines." By Homersham 



mechanics, is the full extent of this disadvantage perceived. The 

 science may be approached with a perfect willingness to acquiesce 

 in its doctrines, but the perversion of undigested experience creates 

 diflSculties and prejudices which not tlie will merely, but great 

 mental strength and long-continued mental habit also, are required 

 to overcome. It becomes, then, a matter of great importance to the 

 student to ascertain before-hand the precise nature of these preju- 

 dices and difficulties. They are manifold : and before they can b« 

 fully understood, some idea must be acquired of the character of 

 the evidence on which the conclusions of the theory of mechanics 

 are founded. 



This evidence is of several kinds : that which will most influence 

 the tyro — that which will always he most valid in popular estima- 

 tion — is the weight of authorities. The testimony, however, of great 

 names, high as it is in itself, is by far the lowtst kind of evidence 

 of the truths of mechanics. A sciolist will stop the mouths of 

 those who know as little or less tlian himself, by quoting the 

 autiiority of Newton, Leibnitz, Euler, the Bernouillis, Lagrange 

 Laplace, or Poisson. The man of science cannot be so answered. 

 To him — to no one else so much— tlie ideas of these master-minds 

 are of the highest importance ; but tliey do not work conviction. 

 Between the effect of Newton's dictum, and of the greater part of 

 Newton's reasoning, there exists that immeasurable difference which 

 intervenes between a very higli probability and absolute certainty 

 In the absence of more exact information, the mere knowledge 

 that a certain conclusion is supported by the opinion of one or 

 more of the great founders of the science, will and ought of itself 

 be a strong argument, but not an insuperable one. To assert that 

 the authorities were fallible, is merely to assert that they were 

 human, and that science is progressive^ 



Another, and a higher, though not the highest, evidence, is that 

 derived from comparing the remote predictions of theory with 

 actual observations. Let us cite an instance. Mathematicians 

 infer from the law of gravitation, that the earth moves round the 

 sun in an elliptic orbit, if the very small perturbations arising 

 from the influence of other celestial bodies be neglected. This 

 prediction as to the eartli's course is so remote a consequence of 

 theory, that it could nut have been immediately foreseen — the 

 theory could not have been shaped merely to meet this particular 

 case. Now, the knowledge of the earth's actual course depends on 

 the evidence of mere eye-sight, and may be ascertained, inde- 

 pendently of all theory, by purely practical observations. How 

 far, then, do these observed results verify the theoretical anticipa- 

 tions .? "If we trace on paper," says Sir J. Herschel, "an ellipse, 

 ten feet in diameter, to represent the orbit in which the earth is 

 moving about the sun, and if we trace by its side the path actually 

 described in its revolution around the sun, the difference between 

 he original ellipse and the curve actually described is so excessively 

 tminute, that the nicest e.mmination with inicrosccpes continued 

 along the outlines of the two curves, would hardly detect any 

 perceptible interval between them." 



Again, it is known that tlie solar orbit slowly changes from age 

 to age. The effect of this variation, Laplace showed to be that the 

 moon moves more rapidly around the earth now than it did in 

 remote times. This result of theory is exactly verified by obser- 

 vation. It has been ascertained, from the records of ancient lunar 

 eclipses observed by the Chaldean astronomers, and subsequently 

 by the Arabian astronomers in tlie eighth and ninth centuries, that 

 the moon's mean motion is increasing by about eleven seconds in 

 a century. 



The action of pendulums, the most delicate and refined instru- 

 ments used for scientific purposes, exemplifies, in a wonderful 

 manner, the predictive power of mechanical philosophy. The 

 earth's rotation causes bodies at the equator to be acted upon 

 by a centrifugal force, in the contrary direction to their weight ; 

 it is clear, therefore, that their tendency towards the earth is 

 diminished. The value of this diminution, as also of its effects 

 on the vibration of pendulums, is determined by theoretical cal- 

 culations, which take into account a large number of indepmdent 

 considerations — the earth's radius, spheroidal attraction, the in- 

 ertia of the pendulum, the effects of thermometric expansion, 

 the barometrical pressure, the resistance of the air; &c. By 

 most elaborate processes, then, it is determined that the Same 

 pendulum which beats seconds in London (that is, vibrates 

 86,400 times in the twenty-four hours), ought to make fewer 

 vibrations by about I-IO at the equator. Also, the number of 

 vibrations which this pendulum ought to make in various other 

 latitudes, north and south of England, have been computed ; 

 and the results have been confirmed by observation, in a re- 

 markable manner. • Pendulums, constructed with the greatest 

 care, have been carried from London to many places on the 



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