AMERICAN INSTITUTE, 559 



Major Serrel found no person in France, England, or this country, who 

 was fully satisfied of the accuracy of Foucault's experiment, and he, there- 

 fore, considers any esperiment which gives absolutely reliable results as a 

 brilliant discovery. He had tried the pendulum experiment himself, but 

 without success : sometimes it would show rotation in one direction, at other 

 times, in the opposite direction. 



. Mr. Garvey explained that when a steel wire and an iron or steel ball 

 was used, terrestrial magnetism would be likely to affect the pendulum and 

 cause its oscillations to take place with reference to the 'magnetic meridian. 

 Also that atmospheric currents would affect it, and that if the center of 

 measurement did not coincide with the center of gravity, or of inertia, the 

 pendulum would be affected by the unequal resistances experienced, from 

 the air, on the parts of the ball at each side of the center of inertia. The 

 error from this cause would be analogous to that which takes place in the 

 path of a ball projected from a smooth-bored cannon. If the ball of the 

 pendulum be caused to rotate, at the same time that it, oscillates, this error 

 will be eliminated as the aim of a rifled gun is made certain by causing the 

 ball to rotate as it moves along. 



Mr. Seeley had tried Foucault's experiment without success. It is a 

 delicate experiment. It seldom succeeds with any one. Mr. Garvey's 

 experiment is also one requiring great delicacy. I do not think it will suc- 

 ceed. We hear of many such experiments but they don't succeed. They 

 require a delicacy of workmanship in the apparatus that cannot be attained. 



Mr. Fisher wished to get a reason for the rate of rotation indicated, for 

 different latitudes, differing one from another. Why does not the indication 

 always continue at fifteen degrees an hour for all latitudes ? Mr. Garvey 

 gave a popular explanation, by the aid of diagrams on the black-board, 

 referring the difference to the fact that the indicating tube revolves on the 

 surface of a cone, not on the fiat surface of a disc. 



Mr. Babcock considered that water in flowing down a vertical tube would 

 take up a rotation of its own which would affect the instrument described. 



Mr. Garvey said that this objection was well taken ; that in the experi- 

 ments which he had tried, he invariably found that result to be produced — 

 hence the reason for detaching the horizontal tube from the vertical one. 



Mr. Seeley introduced the regular subject of the evening. 



"LEAD." 



He could not find the primitive meaning of the word lead or plumbum. 

 Lead was known in the earliest times by almost all nations as a metal, but 

 not as a paint. The American savages used the ore as an ornament, but 

 had never reduced it ; though, if they had employed lumps of the ore about 

 their fires, they would have obtained the metal. This is strange, seeing 

 that they were workers of copper. In the time of Paracelsus, there was a 

 furore for metals over all Europe. The principal deposit of America is 

 in Davidson county, N. C It is found in all rocks; but in the azooio 

 rocks the galena contains a portion of silver, even seven per cent. 



