ON EARTHQUAKES. 
371 
mine the intensity of the remaining force. The former has been the system 
adopted,— directly, in the mode of solid pendulums, and indirectly, by that 
of liquid pendulums,— to use the term of Mr. Mallet, their proposer. 
Immediately after the re-appointment of the Committee, I heard from 
Major Janies that he had adopted, more from necessity than choice, the 
form proposed and adopted by Prof. James Forbes ; and that he had found 
it unsatisfactory, as a purely vertical force tended to produce a lateral move¬ 
ment; and this seems a necessary consequence of a construction which in¬ 
troduces a flexible spring or wire between the pendulum and its support,— 
8i this spring bends, and then, in recovering its straightness, produces a 
lateral vibration in the pendulum ; but ns an instrument bad been made, it 
appeared prudent to submit the proposition to the Committee, as one of 
inquiry, as to the possibility of modifying or improving this specific con¬ 
struction; and I offered a suggestion as to a disc of metal, supported on a 
conical pillar, and armed with a pointer at top, as a construction which might 
avoid the disturbing influence of the vertical component. Prof. J, Forbes 
made some slight modifications in this construction; aud wrote that he 
thought it might be advantageously adopted for determining uoinc forms of 
tli'i possible movements consequent on earthquake disturbance. As such, I 
fitnt it to Major James, advising him to use his own discretion, as it would 
he better to have two of the first construction of Prof. Forbes, than one of it 
and another of the disc pattern. He, however, had two disc Seismometers 
constructed, altering, for convenience sake, the mode of suspension, so as to 
‘•mule the instrument to mark the angular movement below rather than 
wove, us in my suggestion. His proposition to do this 1 also submitted to 
several member* of the Committee; but receiving no suggestions for change, 
~-and indeed from Mr. Mullet a reiteration of his former opinion, that no 
°.' d pflulum could be of any use,— I saw no reason to interfere further 
n 1 the construction; and the instruments arc now before the Section, 
all Hi nwking ali y further observations on this part uf the subject. I will 
RWy t0 the liquid mode of registration—namely, that proposed by 
on!' I • in 1,111 “ Adrairalt y Ma »u»l.'' This is by bent tubes, £' diameter, 
I . ,)ein g vertical and closed, the other horizontal and open, each limb 
-“f , , ut of mercury at the bend. Now, a pointer of cork being 
to iT U | U , lt0 die °P en 0ll, l> a sudden lateral shock would cause the mercury 
ispiace the cork, which would thus mark the extent of the movement, 
ioili tube ? j° iQGl1 together, and facing N.S.E.W., would of course 
•ate the part.cufar ilireetion of the shocks. An inverted syphon tube, 
vertical *1 P[l nc M’l e >, Mr. Mallet also suggested for measuring the 
br , 10c “' Another instrument, on the same principle, is described, by 
Frederie * le mven *' on °f Caeciatore, of Palermo, and is stated by 
intonsb* A r° U ! ,avc keen used for determining the direction and 
inches L earth q uak e shocks in Sicily. It is a circular disc of wood, ten 
eight LnW . Iai,i< ' t ?‘j w [, t , H smooth bottom and surrounded by a rim with 
grooves Pr l° U r 0 the rim is a circular wooden projection, with eight 
the receiv r& T onclin & t(> tb e holes, and intended to convey the mercury to 
vertical ghr^v° r CU |!f ,f acc ^ l Je low them. In this arrangement a purely 
vertical and hor'LT t 1 * m , a , rked a si,n > lai ‘ quantity in each' cup ; but a 
to the more Wo . uld coin l ,lioate each other. 1 do not here allude 
vatiic batterv 1°! ■ “Si* P' T ,sed . Mr. Mallet, with the aid of a gal- 
de >erminaiirm ,e ‘f 19 8tl l' u ^ ? uing ins inquiries with a view to the future 
appears to bi. 1 lL • n ° r ° Pf r ^ ect Instrument; but I will observe, that it 
much increase , 1 °P 1Dl ° n °f several oi the Committee, that the difficulty is 
y en ueavounng to measure all, or even several, of the 
2 b 2 
