COULOMB. 



('■uulmnb. to the temple, which consisted of extensive apartments, 

 _ " v ' — ' or caves, with vaulted roof's, and separated from one ano- 

 ther by walls hewn from the solid rock. They are all 

 supported by pillars cut out of the rock, the largest apart- 

 ments being below, and the smallest above. A very great 

 number of colossal statues, hewn out of stone masses, are 

 placed around the walls. Among these are the gods 

 Brahma, Vishnu, Sheva, Rama, Krishna, Devendra, 

 Kartiguna, and Gannesha, and the goddesses Parvadi, 

 Sarasvadi, and Lakshmi, and the nine different forms 

 into which Vishnu had transformed himself while on 

 earth. Some idea of these temples maybe formed from 

 inspecting Plate CLI. of Civil Architecture. A mi- 

 nute account of the sculptures and ruins, of which the 

 above is a very general description, will be found in the 

 first volume of the Asiatic Researches, by William Cham- 

 bers, Esq. See also Bartolomeo's Voyage to Ike East 

 Indies, (j) 



COULOMB, Charles Augustus, a celebrated me- 

 chanical philosopher, was born at Angouleme on the 

 14th of June, 1736, and was descended from a family 

 which had been distinguished in the magistracy of Mont- 

 pellier. Having been taken to Paris at an early age, he 

 acquired a decided taste for the mathematical sciences ; 

 and with the view of making his knowledge subservient 

 to his promotion, he entered into the corps of military 

 engineers. About this time he went to Martinique, where 

 he was employed by government in several important 

 works; but the insalubrity of the climate, which had al- 

 ready proved fatal to all his companions, compelled him 

 to seek for health in his native country, to which he re- 

 turned, after an absence of nine years. The first me- 

 moir which he laid before the academy was on a subject 

 connected with his profession, and obtained for him the 

 title of a corresponding member. It was published in 

 a separate work, entitled, " Re sur les moyens d'executer 

 sous I'eautoules sortes de travaux hydrauliques sans employ- 

 er aucun epuisement," and was written for the prize propo- 

 sed by the academy of Rouen in 1778. A second edition 

 of it was published at Paris, in 1797. In the year 1779> 

 lie divided with M. Van Swinden, the learned author of 

 the Positiones Physical, the prize for the best construction 

 of ;the magnetic needle, and in the year 1781, he car- 

 ried off the prize proposed by the academy on the theory 

 of simple machines. 



This valuable memoir, which was published in the 

 Memoires des Savans Et rangers, torn. x. p. 163. contains 

 a series of admirable experiments on friction, and on the 

 stiffness of ropes. The subject of friction, which had been 

 treated very imperfectly by Amontons, Bullfinger, and 

 Euler, was here investigated with a degree of ability and 

 success which widely extended the reputation of Coulomb. 

 By using ponderous weights, and by conducting all his ex- 

 periments on a very large scale, he has obtained results 

 equally new and interesting. One of the principal re- 

 sults which he obtained relates to the effect of time in 

 modifying the friction of one body upon another. The 

 friction sometimes reached its maximum after the rub- 

 bing surfaces had been only one minute in contact, and 

 in other cases the maximum effect was not produced till 

 they had been in contact for five or six days. When a 

 body weighing 1660 pounds was laid upon its correspond- 

 ing .surface, it was put in motion by a weight of 64 pounds; 

 but when the contact was continued for three seconds, the 



force required to move it was 160 pounds; and when Coulcnik 

 the contact was continued for six days, it could with dif- ■* "~~<~~ m " 

 ficulty be moved by a force of 622 pounds. These ex- 

 periments were made at Rochefort, where M. Coulomb 

 then resided ; and from the naval arsenals which were 

 under the charge of M. La Touche-Treville, lie obtained 

 every assistance that could facilitate his researches. 



In consequence of the competition for the prize on the 

 subject of the magnetic needle, the attention of our au- 

 thor was turned to the subject which has been the prin- 

 cipal foundation of his fame. One of his antagonists 

 having pointed out a method of removing the effect of 

 torsion, or the resistance which is opposed to the magne- 

 tic force by the stiffness of the suspending wire, Cou- 

 lomb applied himself to investigate the effects of tor- 

 sion, and invented a machine for measuring it with pre- 

 cision. These researches are contained in two memoirs 

 which were published in the Memoirs of the Academy, 

 under the title of Recherches Theoriques et cxperimentales 

 sur la force de Torsion, et sur I elasticity des jih de Me- 

 tal.'* In these experiments Coulomb employed a very 

 simple apparatus. A metallic wire suspended vertically, 

 was firmly fixed at its upper end, and its lower end w as 

 fixed into a cylinder, also vertical, and having a horizon- 

 tal index. By turning the cylinder about its axis the 

 wire is twisted, and when let go, it endeavours, in virtue of 

 its elasticity, to recover its form. The index will therefore 

 oscillate round the axis of the cylinder. The force which 

 produces these oscillations is called the force of torsion, 

 and the angle measured by the arch which the index de- 

 scribes, the angle of torsion. After having deduced the 

 formulae for the oscillatory motion of the cylinder, on the 

 supposition that the reaction of the force of torsion is 

 proportional, or nearly so, to the angle of torsion, Cou-. 

 lomb proceeds to determine by means of these formulae, 

 the laws of the force of torsion relative to the length, the 

 thickness, and the nature of the wires which were used; 

 and from a great number of experiments, he obtained the 

 following results: 



1. For all metallic wires, {when the angles of torsion 

 are not very great, the force of torsion is sensibly pro- 

 portional to the angle of torsion. 



2. The duration of the oscillations is as the square 

 roots of the weights of the oscillating cylinders. 



3. The times of the same number of oscillations are 

 as the square roots of the lengths of the wires. 



4. The momentum of the force of torsion varies as the 

 fourth power of the diameters of the wires ; and, 



5. In metallic wires, the momentum of torsion is di- 

 rectly in the compound ratio of the angle of torsion, and 

 the fourth power of their diameter, and inversely as the 

 length of the wire. 



In the year 1781, Coulomb arrived in Paris, and was 

 immediately elected a member of the Academy. His 

 attention was now directed to the subject of electricity 

 and magnetism ; and the rest of his life was employed 

 in this important investigation. By a series of delicate 

 experiments, he demonstrated that the attraction of mag- 

 netism is inversely as the square of the distance. He 

 improved the dipping needle and the common magnetic 

 needle, and with the aid of theory, he gave a new de- 

 gree of perfection to the method of making artificial mag- 

 nets. The most important, however, of all his results, 

 relates to the effects produced upon the magnetic action 



* See Mem. Acad. Par. 1784. p. 229. 



