Prof. Cayalleri on a New Seismometer. 115 
_ 6th, The resultant of both these elements, or the mixed shock 
itself. 
6th. The inclination to the horizon of the mixed shock. 
7th, The velocity and time of the wave. 
8th. The total intensity of the wave, introducing into it the 
element of time as furnished by the pendulums. 
If, then, as frequently happens, we also know the total dura- 
tion of the earthquake, we may approximately infer its total in- 
tensity. I say approximately, because it appears that the last 
undulations are always weaker than the first or following ones. 
Were it not for this, we might obtain the intensity due to any 
given earthquake by multiplying the intensity of one wave, as 
above, by the number of the oscillations which were made by the 
pendulum in the total time the earthquake lasted. We shall 
conclude the description of this apparatus with a remark equally 
applicable to the other seismometers, which we purpose briefly 
to notice. 
In earthquake convulsions, very irregular or rotatory pertur- 
bations occasionally occur. Our seismometer, although it is 
incapable of noting all, can record the most important of these 
convulsions, and intimate the occurrence of others by the irre- 
gular marks which will be impressed on the ashes. Lastly, 
wherever the centre of effort may be, the ground must be so 
affected as to destroy the apparatus, if happening to be there 
set up. This, however, will not occur once in a thousand times ; 
so that out of a thousand instances the instrument will be of 
service in 999, as may be seen in the repeated shocks which 
occurred in July 1855, at Vispe in the Alps, as observed and 
described by Favre. 
To complete my remarks on seismometers, it is necessary to 
institute a comparison of our seismometer with those that have 
come under my notice. Passing over some which do not deserve 
the name, such as the vessel of water with floating particles (una 
polvere galleggiante) which is spilled by the earthquake, we shall 
mention one attributed to Cacciatore, but really invented by a 
Milanese, as I was assured by the astronomer Carlini. 
* * * * Xk * * * 
The remainder of Professor Cavalleri’s memoir is occupied with 
a detailed description and discussion of the defects, &c. of the 
seismometer of Cacciatore (which he states has received import- 
ant improvements by Coulier, but the nature of which Signor 
Cayalleri had not learnt) ; of Kreil ; of those suggested by myself 
(as extemporaneous instruments only), in the first edition of the 
‘Admiralty Manual ;’ and of that of Prof. James Forbes, 
As these have, however, all been more carefully described, and 
