64 LOCAL VARIATIONS AND VIBRATIONS OF EARTH’S SURFACE. 
travelling fast, such as carriages and cabs, produced far more de- 
cided effects than carts. The only good method of avoiding these 
was to wait till the city had gone to bed. 
ese and many other facts show us that there can no longer 
be any question about the condition of the earth taken as a whole. 
It acts under all the forces affecting it as an elastic ball, yielding 
Patina to increased atmospheric pressure and rising up when that 
is removed, and vibrating readily under volcanic or other impulses. 
The effect of a fall of 1 inch in the barometer, or rather in the pressure 
of the atmosphere, is, however, no small change; it is equal to 
Europe rise during the summer ; and, by reference to the " 
you will see that in our winter (that is European summ 
eastern pier of the Sydney transit also rises , then, several 
observatories in the northern hemisphere taken at random an 
one in the southern hemisphere all find the eastern pier of their . 
transit instruments rising up at the same time of year, the pre- 
sumption that it affects all transit instruments is very strong 
then comes the question, why isit so? It seems hardly worth ‘while 
to discuss the probability of its being due to temperature, for if an 
increase of temperature be the cause of it in the north a decrease 
of temperature can hardly be the cause in the southern hemisphere 
It is evidently something affecting both hemispheres of the earth 
at the same time of year in the same way. Such at least is the 
state of the case as far as the evidence goes. When observatories 
generally have published the sarhiaelien “of their transit instrument 
corrections we shall be in a better position to form an opinion. 
eanwhile, it should be borne in mind that the maxima and 
minima of the curves coincide with the summer and winter 
solstices, and that at these times the sun’s attraction has the great- 
est effect upon the equatorial protuberance of the earth, producing 
a deflection in the direction of the earth’s axis, or in ot ther words, 
a great strain upon the surface generally, and hence possibly a change 
sufficient to be noted in the corrections of a transit instrument, 
The published information is, however, too meagre to justify 
any further speculation in this direction at present ; but if it be 
true that the moon can produce a diurnal strain sufficient to affect 
our instruments, then it is pt reasonable to suppose that the 
sun may annually produce a strai 
In the following diagrams will be found phatolienes eer copies 
ft e; Sydney - 
level ates 1877 to Iason inclusive ; ; level curves < Consaith 
1880 and 1881, for comparison ; temperature curves at Sydne 188 
ried "83, and 84; sis the azimuth curves at a = to 1 ° 
inclusive ; also August t barometer eearen, SOHE 884 inclusi 
