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XLIII. Pendulum Experiments. By ThomasG. Bunt. 

 To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



I HAVE lately been repeating M. Foucault's experiment in 

 my own house, and endeavouring to ascertain with what 

 degree of accuracy it may be performed on a comparatively small 

 scale, and at a much less expense of time and labour than I had 

 bestowed on it on a former occasion. I have accordingly sus- 

 pended, in diflFerent parts of my house, three different pendu- 

 lums, and now send you the results of the experiments I have 

 made with each of them. 



My longest and heaviest pendulum was erected in my stair- 

 case, where, by making an aperture in a landing-place, I obtained 

 a length of 19 feet. Here I suspended from a strong piece of 

 timber fixed across the angle of two walls, the leaden ball of 53i 

 lbs. weight, with which I experimented last summer in the spire 

 of St. Nicholas, and enclosed it in a glazed case, (having a small 

 aperture at the top for the wire,) in order to protect it from cur- 

 rents of air. The azimuth circle, 7 inches in diameter, was fui*- 

 nished with vertical and horizontal adjusting screws, and usually 

 brought within about ^'^th of an inch below the point of the wire 

 projecting from the ball. Parallel lines, g'^th of an inch asunder, 

 were drawn across the circle, by means of which the ellipticity, 

 or semiaxis minor {b), was read off and recorded, in each experi- 

 ment, to the g^udtli of an inch. The advantages of short arcs 

 (which I first perceived and pointed out last summer) have now 

 become more than ever apparent ; so that in the greater part of 

 my recent experiments I have seldom drawn my pendulum more 

 than 1 inch from the perpendicular. Commencing with a semi- 

 arc of this magnitude, my 19-feet pendulum will keep up its 

 vibrations, so that they may be seen, and their azimuthal direc- 

 tion ascertained within 3 or 4 degrees, after a period of 35 or 

 40 hours. I have not, however, introduced into my present 

 series any experiments of long period, but confined myself to 

 those of which the mean ellipticity has been observed and re- 

 corded. 



The centre of suspension of this pendulum is similar to that 

 which I employed at St. Nicholas, and described in my letter 

 contained in your Number for June 1851 ; with this difference 

 only, that a hole is drilled through the axis of the divided screw, 

 into which is inserted a steel cylinder composed of four segments 

 like the screw itself, up which the wire j)asses, and is thus com- 

 pressed between four pieces of hardened and tempered steel 

 instead of brass, which had been found too soft to resist the 



