38 Mr. T. G. Bunt on Pendulum Experiments. 



it, was tapered so as to be larger towards the disc. The wire 

 being passed up the middle of this screw, is tightly held between 

 the four quadrants, which are compressed by a nut. The disc 

 was then screwed down to the floor and leveled by a spirit-level. 



Nearly the whole of the following series of experiments were 

 made with these new arrangements, and they appear to be in 

 every respect much superior to those of the former series. The 

 tendency to elliptic motion in the pendulum-bob was very consi- 

 derably lessened ; and sometimes it would vibrate for nearly three- 

 quarters of an hour without any cUipticity at all. After making 

 and tabulating a mass of experiments, I found the correction for 

 y^^th of an inch ellipticity, in a mean arc of about three feet, to 

 be only 0°*43 per hour ; and from several experiments in which 

 the pendulum was left to vibrate several hours, without receiving 

 a new impulse, I found the apsidal motion of short elliptic arcs 

 to be much below this proportion, though their precise law I do 

 not pretend to determine. 



In the following experiments, occupying rather more than 

 thirty-seven hours, an impulse was usually given to the pendulum 

 about once in an hour. The degree of the azimuth circle cut by 

 the plane of vibration, and the amount of the ellipticity, were 

 usually observed and written down at the end of every quarter 

 of an hour. Those experiments in which the pendulum was left 

 unobserved for a whole hour or more are excluded from this 

 series, and their results given separately. The ellipticities were 

 seldom permitted to exceed 0*2 inch, and a correction for each 

 is introduced into the observed motion in azimuth. Care was, 

 however, taken to make the opposite ellipticities as nearly equal 

 as possible ; and it will be seen below, that, in taking their sum 

 (regard being had to the sign of each), they amounted to only 

 — 0°*32, although they were about 150 in number. 



I find that I was in error in saying that the zero of my circle 

 was in the meridian ; it is not zero, but the division 16° nearly. 



In Table I. I have given my experiments in the order in which 

 they were made, adding just so many together (usually about 

 four) as would make about the interval of one hour for each 

 group. With the number of minutes are given the degrees of 

 motion in azimuth, the con'cction for ellipticity, the part of the 

 circle observed, and the rate of motion per hour, for each of the 

 thirty-seven hours through which the experiments extended. 

 Table II. is deduced from Table L, and shows the mean rate of 

 the motion in azimuth for every 20°, from 0°to 180°. Table III. 

 gives the result of experiments with intervals longer than any 

 contained in Table I., varying from one to four hours, at the 

 beginning and end of which intervals only the pendulum was 

 observed. 



