1069 
In this case the second term will be seen to exert a very high 
influence, which makes itself felt from « — 0,006 onwards. 
Finally another experiment was made to ascertain the influence 
of a lengthening of the time of oscillation by an increase of the 
moment of inertia. For this purpose the copper cylinder was used 
instead of the aluminium cylinder, by which the oscillating system, 
including the sphere, obtained a moment of inertia of 945 C.G.S. 
(7, = 26.70). With this system we found for 
he Water, at-9°S (== 1,000} = 0,01810) 
a=0,0l& + 8,50. 10 #°—3,24, 10-8 2°, 
with 7’= 26.96 and q=0.0924. The deviation is thus somewhat 
larger than in the former experiment with water, notwithstanding 
the increase of 7’; but d has become smaller, which for an equal 
value of Z’ corresponds to a diminution of 4. 
4. On account of practical difficulties involved no attempt was 
made to extend the observations to angles of deviation much smaller 
than .01 of a radian'). On tbe other hand a few more observations 
were made in which the deviations were very large (up to 62). For 
this purpose on the small copper tube which is soldered to the 
lower end of the small glass tube B, of the oscillating system 
(comp. Comm. N°. 1495, IV, 2) a small aluminium dise was placed 
(radius 3 cms; mass 23,7 grms; moment of inertia 144) with a 
cylindrical copper edge, the external cylindrical surface of which 
was provided with a scale-division in degrees. A small telescope 
was focussed on this scale, by which one tenth of a degree could 
be read by estimation. 
To the wooden board which covers the stone pillar at the level 
of the steel pin S¢ which carries the sphere a small clip was fastened, 
by means of which the pin could be gripped and in this manner 
the oscillating system after a rotation through a definite angle (about 
three complete rotations) could be arrested. By removing the spring 
which held the clip closed, the oscillating system was released and 
the amplitudes of the oscillations performed by the system were 
observed, first on the divided disc down to about 5°, and then as 
1) In order to descend to angles ten times smaller the reading arrangement 
would have had to be placed at a ten times larger distance (i.e. 15 meters). In 
itself this would rot have been an insurmountable difficulty, but much higher 
demands would then have been made on the rigidity of the mounting; even now, 
although apparatus and reading-arrangement were placed on pillars built in the 
ground (comp. Comm. N”. 1490, IV, 2), the vibrations occasioned by the passing 
traffic were often troublesome. 
68 
Proceedings Royal Acad. Amsterdam. Vol. XIX. 
