Rev. C. S. Lyman on the Pendulum Experiment. 399 



pendulum by the Florentine Academicians^ but without any in- 

 timatioQ of its cause. That such a motion was to be expected, 

 was also suggested by the Marquis de Poli, (Phil, Trans., 1742,} 

 and by Poisson in 1S37, but without giving the subject any fur- 

 ther attention, or attempting to test it by experiment. 



The observed independence of the plane of oscillation of a 

 ; vibrating sfeel rod inserted in the revolving arbor of a lathe, ap- 



pears first to have suggested to M, Foucault the idea that the 

 plane of vibration of a free pendulum would, in like manner, be 

 independent of the rotation of the earth. 



The experiment was first tried by him with a pendulum six 

 and a half feet ui length suspended from the vaulted roof of a 

 cellar, and with entire success. It was subsequently repeated, in 

 connection with M. Arago, at the Paris Ohservatory, with a pen- 

 dulum thirty-six feet long. This was in February, 1851. Since 

 that time the experiment has excited general interest, and numer- 

 ous repetitions of it have been made both in Europe and America. 

 We propose in tfie present article to give a general summary 

 of information on this subject, derived partly from published ac- 

 counts, and partly from our own experiments, 



1. The method of' saspendon. — Foucault used a fine steel 

 wire inserted at the top into a hole just large enough to receive 

 it, made in a steel plate which was fastened to the ceiling. The 

 same method of suspension was employed by Mr. Bunt at Bris- 

 tol, England, by Profs. Carswell and Norton at Providence, R. L, 

 in the experiments at the Capitol in Washington, atid in those at 

 ■New Haven. Indeed this appears to have been the mode gene- 

 rally adopted by those who have repeated the experiments. At 

 the U. S, x4rmory in Springfield the suspension at top was by 

 means of a pointed steel piv"ot resting on a hard surface, and the 

 same method has been elsewhere tried, both in this country and 

 in Europe, with a view, probably, in most cases, to avoid friction, 

 l^tn in others, perhaps, to obviate the supposed prejudicial effect 

 ^f the rotation of the poiiit of support— a matter which, as we 

 shall see, is of no consequence whatever. Others have devised 

 niore complicated modes of suspension, such as gimbals with 

 knife edge pivots, the principle being that on which chronome- 

 ters, marine compasses and barometers are suspended. 



But besides the danger of errors arising from imperfect work- 

 nianship in these complicated devices, it is not certain that they 

 present any advantages over the first named method, viz., the in- 

 sertion of the upper end of the wire by soldering, or otherwise, 

 in a firm metallic support. If the wire is equally flexible in all 

 directions, this method is as good as can be desired, and whether 

 the wire is thus flexible or not, may be ascertained qf periment- 

 ally in the manner suggested by Prof Bache at Washington; 

 namely, by placing the portion of the wire at which the flexure 



