30 NEW YORK STATE MUSEUM 



undisturbed strata of clay. The distance to solid rock is not known. 

 The pier is isolated from the ground by a narrow trench extending 

 on all sides of the base of the foundation. There are two of the 

 horizontal pendulums, one placed so that its axis lies east-west and 

 the other north-south when at rest. They are supported by stand- 

 ards at one end while the outer extremities carry massive lead 

 weights to which are engaged recording arms delicately pivoted 

 and capable of adjustment so as to magnify or diminish at will 

 the motion imparted to them. A multiplying ratio of lo has been 

 found to give good results at Albany. The recording arms register 

 the movements by means of a needle, the point of which is in con- 

 tact with a band of smoked paper wound around the outer surface 

 of a drum. The drums are driven by clockwork at the uniform 

 speed of one revolution an hour; their axes are cut with screw 

 threads which cause them to move laterally as they revolve. An 

 independent clock of better construction serves to record the shorter 

 time intervals by opening an electric circuit which, passing through 

 small magnets, causes an arm to press down upon the paper at the 

 lapse of each minute. While in operation the instrument thus 

 traces a continuous line in the form of a spiral on the smoked sur- 

 face of the paper which also shows a series of dots regularly spaced 

 representing the minute intervals. When the record is removed 

 from the cylinder and stretched out in a plane, the spiral line be- 

 comes, of course, a series of parallel lines. In case any disturbance 

 lias occurred during the time of making the record, the line shows a 

 series of wave motions of greater or less amplitude according to 

 the violence of the disturbance. 



The following constants are given in connection with the 

 description of the records to facilitate comparison with those ob- 

 tained at other stations. The latitude of Albany is n. 42° 39' 6" 

 and the longitude w. 73° 45' 18". The foundation of the instru- 

 ment is approximately 85 feet above sea level. Each pendulum 

 including arm weighs 24 pounds 14 ounces or 11.283 kilograms, 

 and the distance of center of gravity from rotating axis is 84.6 

 centimeters. The period of the pendulums (time required for a 

 complete swing) during the time in which the instrument has been 

 operated, has been found to vary, and it has been necessary to re- 

 adjust them occasionally in order to obtain satisfactory results. 

 Each readjustment involves a slight change in the period. It has 

 been the aim to maintain a period of about 30 seconds and the varia- 

 tions have usually not exceeded five seconds. 



