Mr. Mauer on Earthquake Registration Instruments 109 
EXPLANATION OF THE PLATE. 
Fig. 1 is a side elevation of the whole instrument. 
Fig. 2 is an end elevation of the same, omitting the horizontal element 
tubes, to avoid confusion. 
Fig. 3 is an elevation of one face of the transit dials. 
Fig. 4 is an enlarged view of the electro-magnetic apparatus, for the move- 
ment of the registering pencils. 
Figs. 5 and 6 are enlarged views of the upper and lower bulbs of the oscil- 
lation tubes. 
Fig. 7 shews the mode in which the paper is ruled for the registration cylinder. 
The same letters refer to all the figures, as far as is possible. 
The instrument is firmly secured to the surface of a large, heavy slab of 
marble, tenoned into three vertical blocks, a, a, a, which are built into masonry, 
forming the floor of the observatory, 6,5. c¢, a cylinder, formed of staves of red 
cedar, screwed to the circumference of two or more sets of brass arms, and pre- 
pared to receive the sheet of ruled paper, ABC, Fig. 7. The circumference of 
this cylinder is 180 inches, and it is caused to revolve once in a minute, being 
connected with the astronomical clock by the shaft e ; any point in the circum- 
ference, therefore, passes over three inches in a second of time. The horizontal 
axis of the cylinder is supported upon the columns d, d. 
At either side of the cylinder, and parallel to its axis, is a straight bar of 
brass, ff’; each of these carries three separate sets of marking apparatus, at 
equidistant intervals along the bar, the interval being equal to the spaces 
AB, BB’, B’/B’, upon the ruled sheet, viz. twelve inches; and, by means 
of the endless screw, », working into a screw rack on the lower edge of each 
of the bars, and rotation given to the screw and shaft, A, by the clock, a slow 
motion, in the direction of its own length, is given to each bar, so that it moves 
over twelve inches in twelve hours; and then, by a simple coupling, attached to 
the moving gear of the clock, the motion is reversed, and the bars move in the 
opposite direction over twelve inches, at the same rate as before, and so on. 
