Bull. — On a Xew Form o) Seismograph. 7 J 



to the plane of the base or stand, the markers resting upon the 

 smoked glass, which presents an unbroken dark surface. Now 

 it follows that any alteration in the position of the base, such as 

 an upheaval, or the reverse, of the extremities, as would be 

 caused by an earthquake, must result in a corresponding mark 

 on one or both of the smoked glasses from their contact with 

 the points of the markers, and thus we have the register of the 

 shake. The marks on the glass are rendered the more notice- 

 able on account of the white backing showing through, where 

 the smoke film has been removed. 



When I first constructed the machine, instead of rigid metal 

 markers on hinges I used fine wires, bent so as to form a weak 

 spring ; and at the points were soft lead pencils, which were to 

 mark the seismic disturbances on a surface of hard drawing- 

 paper instead of glass. But, although fairly successful, I found 

 that after the machine had been undisturbed for any length of 

 time the points had a tendency to settle themselves in the 

 surface of the paper, and a slight shake was not enough to 

 displace them, but the movement became expended in the 

 suppleness of the springs. Accordingly, I substituted the glass 

 surface for that of paper, and the direct-acting hiuged markers 

 instead of the springs, and I think we have now an instrument 

 which has the recommendation of being simple in construction, 

 inexpensive, and reliable. 



Of course the instrument before you is capable of improve- 

 ment, in the way of more skilful workmanship, as it is not 

 possible with only a few tools and a kitchen table to turn out 

 very highly finished work ; and a real improvement could be 

 effected by substituting an agate centre for the metal one I have 

 used. However, I have,- 1 think, succeeded in producing an 

 instrument, which if properly set up, free from disturbing in- 

 fluences apart from those which its object is to register, will 

 give satisfactory results, and which, from its inexpensiveness 

 and utility, I venture to suggest, might be supplied by the 

 Meteorological Department to numerous stations throughout 

 this colony, and thus allow of a comprehensive and reliable 

 record being kept of the seismic movements so often occurring. 

 I may state that a large number of instruments for this purpose 

 are in use in other countries, and it is only about two years ago 

 that a considerable sum was granted by the Indian Government 

 for supplying all the Meteorological Stations in Bengal and 

 Northern India with instruments. The form of these instru- 

 ments I have not the least idea of, but I have no doubt that 

 they are much more elaborate, and certainly more costly, than 

 the one I have shown you this evening. 



