ANNUAL OF SCIENTIFIC DiSCOYKKY. 



clocks into electro-chronographs. The index or a pointer to the pen- 

 dulum passed through a globule of mercury at the lowest part of the 

 arc of each vibration, and while this pointer was in transit through 

 this globule, the circuit was complete, and the recording pen made a 

 dot oa the registering surface. The other globule was placed in the 

 upper part of the clock, and so situated that a little metallic pin at- 

 tached to the axis of the seconds wheel would pass through it at every 

 sixtieth second. As the circuit through this globule was the shorter, 

 the fluid, abandoning the long one through the pendulum, would take 

 ihe shorter route back, and the pen would thus omit to make a dot at 

 the completion of every minute. If we suppose the mean-time and 

 f-i iereal clocks each to run with a rate equal to Os. 0, and their pens 

 each in connection with the register, we shall find that the pen of the 

 latter will make 366 dots while that of the former is making 365 near- 



o 



I//, so that if the paper move under the pen at the rate of an inch per 

 second, the distance between the dots of the two pens at a given sec- 

 ond will differ from the distance between them the next second the 

 365th part of an inch nearly. Lieutenant Maury illustrates what he 

 means, and remarks that by a powerful microscope it would be possible 

 to measure with considerable accuracy the 36,500th part of a second. 

 With such refinement in the recording and subdivision of time, if 

 two experimental pendulums, nearly duplicates of each other, were 

 freely suspended and vibrated, the one in New Orleans, and the other 

 near the same meridian on the borders of the great American Lakes, 

 for instance, and if these pendulums were further so arranged as to 

 make and break circuit, so as to record their vibrations in Washing- 

 ton with the standard clock of the Observatory, and if. after these vi- 

 brations had been continued till one pendulum had gained a vibration 

 upon the other, the two were made to change places, and vibrated for 

 a like period, we should, theoretically at least, have afforded to us 

 rare facilities for determining an arc of the meridian. If now the two 

 pendulums were placed on the same parallel of latitude, one on the 

 Atlantic and the other in the Mississippi valley, for instance, and 

 vibrated, reversed, and vibrated as before, the data would be complete, 

 theoretically speaking, for determining both figure and density. 



By vibrating one pendulum on a mountain and another on the sea- 

 shore, or at some known elevation above tide-water, we should in the 

 same manner procure the date for determining the difference between 

 the distance of the two stations from the centre of the earth, that is, 

 the height of the mountain. In a similar manner might be determined 

 the differences in the density of the strata interposed between the 

 centre and surface of the earth at different places, and also, from the 

 influence of the moon on the pendulum, we might derive the elements 

 for determining the mass of that planet. This is all true theoretically, 

 but whether it could be done in practice is perhaps doubtful. 



Lieutenant Maury also stated that experiments already made en- 

 couraged him to hope that the electro-chronographic clock might be 

 used, not only to drive the machinery of the registering apparatus, but 

 to drive the clock-work of the equatorial also. " 



