CATALOGUE. — MAGNETICAL EXPERIMENTS. 



439 



From the Journals of the Royal Inslilulion. I. 134. 

 Extract from the Decade Philosophique, No. 21. 



National Institute. Experiments showing that all bo- 

 dies are subject to the magnetic influence, even in a degree 

 which is capable of being measured. 



These experiments were made by Mr. Coulomb, and re- 

 peated by him before the Institute. He employed all the 

 substances that he examined in the form of a cylinder, or a 

 small bar J he suspended them by a thread of silk in its na- 

 tural state, and placed them between the opposite poles of 

 two magnets of steel. Such a thread can scarcely support 

 more than two or three drachms without breaking ; it was 

 therefore ruicessary to reduce these needles to very small di- 

 mensions. IVIr. Coulomb made them about a third of an 

 inch in length, and about a'thirtieth of an inch in thick- 

 ness ; and those of metal only one third as thick. 



In making the experiments, he placed the magnets in the 

 same right line. Their opposite poles were separated about 

 a quarter of an inch more than the length of the needle 

 which was to oscillate between them. The result was, 

 that of whatever substance the needles were formed, they 

 always ranged themselves accurately in the direction of the 

 magnets ; and if they were deflected from this direction, 

 they returned to it with oscillations, which were often as 

 frequent as thirty or more in a minute. Hence, the weight 

 and figure of the needles being given, it was easy to deter- 

 mine the force that produced these oscillations. 



The experiments were made in succession with small 

 plates of gold, silver, copper, lead, and titi; with little 

 cylinders of glass, with a bit of chalk, a fragment of bone, 

 and different kinds of wood. 



In the course of his lecture on magnetism on the 3oth of 

 April, Dr. Young repeated some of these experiments with 

 wires of different kinds : one of them was of tin, and sus- 

 pended within a cylindrical glass jar by a single silk worm's 

 thread : its oscillations were so slow as to occupy several 

 minutes, and it was scarcely affected by turning the cross 

 barto which the thread was attached ; so that the suspension 

 «iust have been sufficiently delicate : under these circum- 

 stances the opposite poles of two strong magnets were ap- 

 plied close to the jar, and at the distance of about twice the 

 length of the suspended wire : but the effect was absolutely 

 imperceptible : in the morning indeed, there had been an 

 appearance of oscillations occupying about a minute, and 

 tending to the direction of the magnets, perhaps derived 

 from some superficial particles of iron which had lost their 

 magnetic property by oxidation in the course of the day. 

 There must at any rate be a doubt whether the presence of 



a quantity of iron, too small to be ascertained by chemical 

 tests, might not have been the cause of the effects described 

 by Mr. Coulomb, although they indicate a force something 

 greater, upon a rough calculati6n, than one 2000th of the 

 weight of the substance, Y. 



P. 217. Note on Mr. Coulo.mb's Experiments on Mag- 

 netism. 

 We find in No. 3, Tome 3, of the Bulletin de la Societe 

 Philoraathique, an account of Mr. Coulomb's further experi- 

 ments on magnetism. They appear to have been made 

 with great precaution, and they tend to confirm the opinion 

 already advanced in these Journals, p. 135, that the greater 

 part, if not the whole, of the effect observed was owing to 

 the presence of iron. For it appears that, according to the 

 method employed in the purification of the metals exa- 

 mined, their apparent magnetic power was very materially 

 different. Mr. Coulomb observes that, upon this founda- 

 tion, we may make.the action of the magnet, upon a needle 

 thus suspended, a very useful instrument in chemical exa- 

 minations ; for he finds that the attractive force is directly 

 as the quantity of iron in any mixture ; and, according to 

 its magnitude, we may estimate that quantity, when it is so 

 small as wholly to elude all chemical tests. 



Supposed Magnetism of Animals. 



Schilling on the magnetism of the gymnotus 



electricus. A. Berl. 1770. 68, 

 Against Schilling. Ingenhousz Verm. schr. 



271. 

 Spallamani a Lucchesini. Pav. 1783. 

 Three essays in VanSvvintien's Recueil. 

 Andry and Thouret. Mem. de la Soc. de 



Med. 

 Saurine on animal magnetism. Roz. 



XXXVI. SOS. 



Particular Experiments and Pheno- 

 mena. 



Desaguliers's experiments. 



Knight's experiments. Ph. tr. 1747- XLIV. 



6.56. 

 Waddel and Knight on the destruction of 



polarity by lightning. Ph. tr. 1740. 



XLVl. 111. 



