126 F. OMORi : 



the real earth movements will at least be distinguishable from 

 the proper vibrations of the pendulum. 



6. The writing pointer, sliown in plan and elevation in fig. 

 3, consists of a small steel axis, /, 3 mm. in diameter and 5 cm. in 

 height, rigidly attached to a light lever, mn, whose shorter 

 forked arm, m, is of brass, and whose longer grooved arm, n, 

 is of alminium. The axis is pivoted in a vertical position between 

 two small conical sockets fixed in an inverted stirrup, o, which is 

 adjustable along the horizontal metal bridge, p, supported on two 

 stout wooden posts, q, in rigid connection with the ground. 

 (See fig. 4). 



Between the two limbs (fig. 4) of the shorter arm, m, of the 

 pointer there is fitted exactly a highly polished small axis, r, 3 

 mm. in diameter and 3 cm. in height, which forms the prolonga- 

 tion of the central line of the heavy cylinder, a, and which is 

 pivoted in a stirrup, S, fixed to the latter. 



To a small U-shaped frame of brass, t, at the end of the 

 alminium arm of the pointer is hinged an exceedingly light writing 

 index, u, made of a thin triangular piece, about 5 mgm. in weight, 

 cut from a watch spring. The point of the index rests on the 

 record-receiving smoked paper wrapped round a light wooden 

 drum. (See § 7). 



The effective lengths of the two arms, m and n, of the writing 

 lever are respectively 28 and 280 mm., the pointer thus multiply- 

 ing 10 times the horizontal motion of the ground. 



It will be observed that the pressure, which the writing index 

 exercises on the record -receiving smoked paper, is a small weight 

 of only ^ mgm., equivalent to one-third of the weight of the index, 

 and this circumstance reduces the friction between the index point 

 and the paper to a minimum. Again, the capability of free 



