CHAP. IV., 2.] 



MECHANICS. ROBISON- COULOMB. 



75- 



my to their simplest and most geometrical elements. 

 But the result (as might have been foreseen) was in 

 many cases a wearisome prolixity; and originality 

 could not be expected in these departments without 

 applying the continental improvements in analysis : 

 not that Dr Robison overlooked these ; but he took 

 little pleasure in them ; and as regards Physical As- 

 tronomy he adhered to the older methods. Having 

 been so long at St Petersburg, the writings of Euler 

 must have been familiar to him, as indeed they evi- 

 dently were as far as regards all subjects connected 

 with mechanics : he justly, however, considered Euler 

 as a superficial natural philosopher, though an in- 

 comparable mathematician. 



(337.) As a lecturer in his own department, Kobison was 

 obison as ^\ ie m0 st eminent of his time, at least in Britain. That 

 r ' his courses were not considered popular will easily be 

 understood from a slight inspection of his writings. 

 The demonstrations were long and copious, but too 

 rapidly delivered. "The singular felicity of his 

 own apprehension," says Mr Playfair, " made him. 

 judge too favourably of the same power in others." 

 The lectures must have abounded in practical details, 

 which ordinary students rarely appreciate ; and they 

 were deficient in experiments, which unquestionably 

 arose from no want of the ingenuity necessary either 

 to invent or execute them. On the other hand, the 

 effect of his discourses was greatly enhanced by 

 his striking and energetic delivery, and by the stores 

 of his memory, which often recalled the incidents of 

 the stirring life in which he had once been engaged ; 

 and to the more thoughtful and philosophic they 

 were rendered at once attractive and elevating in no 

 ordinary degree by the strain of fervent thought by 

 which they were accompanied, and the impress which 

 they frequently bore of the pure morality and ex- 

 alted piety of their author. 1 



(338.) Apart from his local usefulness as a professor, we 

 is philo- re g ar( J D r Robison's place in science as eminent 

 aracter. c hi en " v on account of the sagacity with which he ap- 

 plied knowledge to practice, and analysed complicated 

 effects of force as manifested in engineering con- 

 structions. This he did so ably as to guide future 

 practice, and to reflect much light on the theory of 

 solids more or less elastic and tenacious, and subject 

 to the intricate strains which gravity produces. The 

 difficulty and merit of these investigations will best 

 be gathered from the slow progress of his successors 

 in the same field. The criticism with which his 

 writings abound on the theories of even his more 

 celebrated contemporaries and predecessors show re- 

 markable acuteness, patience, and independence of 

 thought. We may perhaps sometimes think him pre- 

 judiced, but his decisions are never uttered without an 



elaborate statement of reasons, nor ever sullied by the 

 suggestions of jealousy or self-conceit. Had he been 

 an accomplished analyst he must have been less dis- 

 tinguished in the equally important walk in which 

 he stood pre-eminent. The limits of human life and 

 faculties prevents universal attainment, but he was 

 surely no mean philosopher of whom the sexage- 

 narian James Watt could say, " He was a man of 

 the clearest head and the most science of anybody I 

 have known." 2 



Amongst the contemporaries of Robison was one (339.) 



whose acquirements were in many respects very si- Coulomb 



i , , -. -i , ., , , . 3 * on friction 



milar to his own, and who contributed, in a degree and p as8 i ve 



second to no other philosopher of his day, to pro- strength, 

 mote sound views in the very same branches of 

 science. CHARLES-AUGUSTIN COULOMB (born 1736, 

 died 1806) was, like Robison, addicted through life 

 to practical enquiries, and was intimately acquainted 

 with all the details of the civil engineering of his 

 day. To him we owe a correct knowledge of the 

 laws of friction in most ordinary cases, and the right 

 application of them to the theory of machines, and 

 to that of the stability of structures. In a very re- 

 markable paper, published in 1776, he analysed, from 

 the basis both of theory and experiment, the manner 

 in which columns of masonry give way under longi- 

 tudinal pressure ; not, as had previously been sup- 

 posed, by flexure under the imposed weight, like a 

 steel spring or a rod of deal, but by the sliding of 

 one portion of the column over another, at an angle 

 determined by the cohesion of the stone, and capable 

 of being reduced to a problem of maxima and mi- 

 nima. This important principle is now known to 

 apply to wrought and cast iron, and many other sub- 

 stances. 



One of Coulomb's happiest investigations was on (340.) 

 the force of torsion, or the resistance of wires to Q torsion, 

 twisting ; which he showed to vary directly with the 

 angle of torsion, inversely as the length of the wire, 

 and directly as the square of its section. These me- 

 chanical principles he applied with address to deter- 

 mine the viscosity of fluids, and with still more con- 

 summate skill and success to the measurement of 

 electrical and magnetical forces by the construction 

 of a Torsion Balance, similar in principle but ante- 

 rior to that employed by Michel 1 and Cavendish for 

 estimating the force of gravity. 



Coulomb's researches on electricity (which have (341.) 

 been only partially published) will be made the sub- His r *- 

 ject of discussion in another chapter of this Disser- resem bi e( j 

 tation ; they were the most sustained and elaborate Robison's. 

 of his investigations, and display very considerable 

 mathematical resources. In this respect he had a 

 superiority over Robison, who, as we have seen, cul- 



1 See Dr Chalmers* Life, vol. i. That great man had a peculiar veneration for Dr Robison, and is understood to have received 

 impresaions from attending his lectures which materially influenced his future life. 



2 Mechanical Inventions of James Watt, ii., p. 290. 



