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SCIENCE 



[N. S. Vol. XXV. No. 638 



cumference, and moving in opposite direc- 

 tions, one forward and the other backward, 

 gives a vibratory motion to the vertical 

 arbor K, and as the regulator or balance 

 was fixed on this arbor, it was thus made 

 to vibrate backwards and forwards at every 

 push of the escapement wheel upon the pal- 

 lets, the period of the vibration being regu- 

 lated by the position of the small weights 

 TO, m on its arms. Thus the whole dura- 

 tion of a vibration was the measure of 

 time, and the wheels and pinions were em- 

 ployed first to transmit the maintaining 

 power to the balance, and secondly to num- 

 ber the vibrations and indicate them in 

 visible form by a hand on a dial plate. 



FiQ. 4. View of de Vick's Escapement Wheel 

 from above. 



Fig. 4 gives a view of the escapement wheel 

 looking from above. The pallets were 

 placed at about 90° from each other on the 

 arbor or verge of the balance, so that when 

 one of them was parting with its tooth of 

 the escapement wheel, the other was in a 

 situation to receive the opposite one imme- 

 diately, but the motion of the verge will 

 not be at once reversed. The escape wheel 

 will recoil until the impetus of the balance 

 is exhausted. 



The substitution of the main spring for 

 a large heavy body as a first mover con- 

 stituted a second era in modern horology, 

 from which we may date the origin of the 

 fusee, or mechanism for equalizing the 

 variable power of a coiled spring. 



While the date at which the first port- 

 able clock was made may not be definitely 

 stated, it was certainly as early as 1525, 

 as the Society of Antiquaries in England 

 has in its possession one made in that year 



by Jacob Zech at Prague, the inventor of 

 the fusee. Its construction differs ma- 

 terially from that of De Vick's clock only 

 in that it has a spiral spring with a fusee 

 instead of the driving weight. 



Such was the state of clockwork when 

 Galileo, the celebrated philosopher and 

 mathematician, while watching the vibra- 

 tions of the great bronze lamp swinging 

 from the roof of the cathedral of Pisa in 

 1583 observed that, whatever the range of 

 its oscillations, they were invariably exe- 

 cuted in equal times. Because of this iso- 

 chronal property of a vibrating suspended 

 body the pendulum was introduced as the 

 regulator of clockwork, thus inaugurating 

 the third era in the development of the 

 modern clock. 



The honor of being the first to apply a 

 pendulum as a regulator of clockwork is. 

 claimed for several clock-makers. 



The earliest of these is, I believe, Richard 

 Harris, who is said to have made a pendu- 

 lum clock for St. Paul's Church, Covent 

 Garden, in 1641. Vincent Galileo claims 

 to have applied his father's discovery to 

 the construction of a pendulum clock in 

 1649, but does not seem to have made the 

 fact public until after Huyghens in 1657 

 presented to the States of Holland a clock 

 controlled by a pendulum, claiming for 

 himself the invention of this form of con- 

 trol. Certain it is that Huyghens gave 

 much study to the mathematical theory of 

 the pendulum, and proved that in order 

 that pendulum vibrations of different 

 lengths should be strictly isochronal, the 

 pendulum should vibrate between cycloidal 

 cheeks. Such an arrangement he intro- 

 duced into his clock of 1657, which also 

 contained the famous Huyghens loop in 

 connection with the winding apparatus. 



With the verge escapement. Fig. 4, the 

 one in use when the pendulum was applied 

 to clockwork, and which required a long 

 arc of vibration for the escapement of the 



