70 Transactions. — Miscellaneous. 



the tube like a piston. The point of this pencil rested on the 

 table or base of the apparatus, at the centring point of lines 

 drawn from the four cardinal points. This weight I suspended 

 by a fine brass wire from the centre of a beam, supported 

 on two tall uprights from either side of the wooden table or 

 stand, on the upper surface of which I fixed a paper showing 

 the points of the compass before mentioned. Of course, any 

 motion taking place at the base, such as the movement of an 

 earthquake, would cause a corresponding pencil-mark on the 

 diagram in the direction of the disturbance, it being understood 

 that the suspended weight remained quite motionless ; bat I had 

 to discard the scbeme as being only partially successful, owing 

 to the fact of the earth's motion being communicated (to a 

 certain degree) to the pendulum as well as to the base : whereas, 

 for accurate results, the pendulum should have been disconnected 

 from, and independent of, the diagram, or part which received 

 the eartbquake motion. 



My next effort resulted in the Seismograph which I have to 

 bring under your notice this evening, and I am pleased to be 

 able to state that I have had proofs that satisfactory results are 

 obtainable from it. You will observe it consists mainly of an 

 inverted basin, heavily weighted round the edge, and balanced on 

 a 6teel point, the centre of gravity being maintained by means of 

 a disc of steel fixed in the centre of the basin. 



The pointed steel rod is firmly fixed in the centre of the 

 stand, which is a substantial wooden one, and from its four sides 

 rise a like number of slight wooden uprights, representing the 

 four cardinal points, and also intended to receive the delineation 

 of the earthquakes as received from the pointers attached to the 

 basin. 



On the inner faces of these uprights is fastened a piece of 

 white paper, and over the paper is a piece of sheet glass, the 

 surface of which is smoked over, and the points of the markers 

 rest against this smoked surface. The markers are made of 

 metal, and are hinged to the rim of the basin, allowing the 

 pointed extremities to rest easily upon the glass. A small piece 

 of lead is attached to the under-side of each marker, so as to 

 render the pressure sufficient to keep the point and the glass 

 surface in constant contact. I should mention here that I only 

 use two of the uprights, and have only two pointers, for the 

 reason that one answers equally for the north and south, and 

 the other for east and west, and the use of four would, no doubt, 

 tend to lessen the susceptibility of the instrument. 



Having now described the form of the instrument, I will 

 explain its action, though I think but little need be said on this 

 point, as the apparatus is so simple that no doubt you will 

 already have understood its action. In the normal condition of 

 the machine, the rim of the basin preserves a position parallel 



