( 11 ) 
I Cik = 
sin (p cos <psina = p cos x 
we then find for the theoretical value: 
K % = 0".00085 , x = 305°.5. 
From the data of Table I we find, however, for the values (8) 
quantities, which are equal in sign but which differ for the rest 
pretty much, namely: 
„ \ 3.97 = R 
K, cos Cn = J 1Q 7 y _ q 
4.10 = R! 
16.34 = Q 
So here too we must assume that S 2 is not constant and that 
there is a semi-annual variation in the semi-diurnal inequality which 
indeed is immediately evident from the amplitudes of Table I on 
account of the inequality of the two maxima and minima. 
If, as above, we represent the S 2 tide by 
{S a + L cos (60 a — m)\ cos (30 t — C) 
we then find out of the four equations 
L cos C cos m -f- K 3 cos C 2 k — R 
LcosCsinm + K,sinCu = Q 
L sin C cos m - j- K t sin C 2]e = R' 
. L sin C sin rn - K % cos C 2 k = Q 
as the result of the investigation: 
K j Calculated 0".00085 cos (2 t — 305°.5) 
a j Observed 0".00070 cos (2 t — 260°.6) 
and for the semi-diurnal inequality : 
0".00244 {1 + 0.574 cos (60 * — 158°.6)j cos(2t— 277°.7) 
This result justifies the expectation that if monthly means of the 
diurnal variation are available calculated over a greater number of 
years and by preference over years in which the declination of the 
moon is great, also the calculation of the small tide K 3 can be made 
with all the looked for accuracy. For, at the greatest declination of 
the moon the amplitude of K 2 is almost twice greater than at the 
smallest. 
Out of the monthly means of the diurnal variation for the second 
horizontal pendulum set up at Potsdam these sidereal tides do not 
admit of a deduction. The continual displacements of the zero point, 
considerable for both instruments, surpass for this instrument all 
the small regular movements entirely. 
A determination of the siderial tides might thus serve as a 
criterion for the quality of seismic instruments. 
