88 REPORT—1858, 2 
finite, but that the maximum varies, being on an average five years after the 
minimum, and that nine minimum periods exactly make up each century ; 
adding, that all the notable apparitions of solar spots on record agree with 
this rule. Other papers on this subject will be found, with details in the 
‘Ast. Nach.’ and ‘ Pogg. Ann.,’ from 1850; and in ‘ Silliman’s Journal,’ 
vol. xxv., some remarks of Reichenbach are worthy of attention. He ob- 
serves that the period of Jupiter is 11°86 years, and that there are certain 
coincidences between the planet’s periodic returns and those of the solar 
spots,—adding that their conjoint magnetic effects upon our planet, in rela- 
tion to the magnetic periods above referred to, cannot but be great. See also 
‘Gilbert’s Annalen,’ vols. xv. and xxi., for Ritter’s memoirs on the subject ; 
and “ Hansteen on the Relations between Earthquakes and the Aurora,” in 
‘ Bull. de l’Acad. de Bruxelles,’ 1854, t. xxi. 
I am myself indebted to my friend Dr. Robinson, Astronomer Royal, 
Armagh, for much of my information upon the subject, which connects. 
itself with our own in relation to the preceding reflections, and through the 
singular point of coincidence as to periodic recurrences in both-—the one 
presenting traces of being in time a submultiple of the other. But at present 
this must all be taken for what it is worth, and no more: 
It may be suitable to remark here, that the movements of the inclination 
magnetometer as well as of the barometric column, of which several have 
been of late years recorded as occurring at the time of earthquakes, are 
most probably merely mechanical and due to the shock movements direct. 
This has been ascertained by Kreil at Vienna, and Padre Secchi at Rome 
(see also Perrey’s ‘Mem. Europe and Africa,’ p. 11); and such appears to 
have been Humboldt’s view (though expressed with some qualification) 
at the date of publication of ‘ Cosmos.’ 
The following is a translation of Zantedeschi’s expressions of his own views 
as to the occurrence of a terrestrial, or rather ¢errene tide, probably better 
named, if it exist, the elastie tide :— 
“On the Influence of the Moon upon Earthquakes, and on the Conse- 
quences probably derivable as to the Ellipsoidal Figure of the Earth and 
the Oscillation of the Pendulum. By M. F. Zantedeschi.” Comptes Rendus, 
Séance du 2 Aout, 1854. 
“TJ have thought for a long time that the form of the earth cannot always 
be the same, but that it presents an incessantly ckanging elliptical form, 
that is to say, having a continued tendency to become protuberant in the 
directions of the radii vectores of the two luminaries which attract it, the 
sun and the moon. I have always believed that a direct proof of it might be 
obtained by determining a point in the heavens at the epochs of the spring 
tides, and at that of the Quadratures. This point must appear lower at the 
epochs of the high tides and of the Syzygies. The Imperial Observatory of 
Paris, with the means that it has at its disposal, could prove if this difference 
be observable, and especially now, that, thanks to the labours of M. Froment, 
dividing has been made so exact as to admit of measuring with the greatest 
precision a difference of ;1,5th of a millimetre between two consecutive 
visible horizontal lines. 
“T have always assumed that a compensation pendulum of such a length 
that it exactly beats seconds at the epoch of the quadratures and of the neap 
tides, must beat more slowly at the epoch of the spring tides, from the 
transit of the moon over the meridian of the given place, and at the epoch 
of the syzygies; and, taking from this fact that the variations of the force 
of attraction upon the mass of the earth are continuous, I have concluded 
from it the necessity for astronomy to take account of these times; and 
