^^ Compensation pendulum. 



expansion and coiitvaction of it must be taken into consi- 

 deration. 

 Sannosed ob- ^^ ^^^ ^^*^" ^^^ opinion of some mecbanists, tbat zinc is 

 jeciion to zinc an unfit substance for a compensation-pendulumj because 

 unfounded. ^^^ |^.,^,g thou-ht it too soft for tbe purpose, and that af- 

 ter bei.ig bealed or cooled to a considerable degree, it does 

 not return to its orij^ynal dimensioos. If that was really 

 the^ease, no doubt but it would be a general one common 

 to all metals in a greater or less decree; but from the ex« 

 perimeats and observations I have made on zinc pendulums, 

 I am fully satisfied there is no foundatioiv whatever for 

 Pcndulnm at such an opinion. Some time in tbe latter part of last sum- 

 fc'ist continually mer, I however noticed a circumstance, that made me doubt 

 retar e , ^^le matter — for when I first uaed my zinc pendulum, I never 



could bring the clock to keep the same rate two days toge- 

 ther, but it was continually retarded, whether I used the 

 lamp or not; and had I not before observed a similar effect 

 on a lever pendulum, that was made of brass and steel, I 

 Tin? common should have ascribed the cause whotly to the softness of the 

 toothers. zinc rod ; but by constantly comparing its daily rate with 



one that had been going a longer time, I found this retard- 

 ing property gradually wore off, and in less than a month 

 would become quite settled to the rate that it would after- 

 wards keep. By subsequent experiments with the lamp too, 

 I have constantly found, that all the pendulums I have 

 liitherto tried kept precisely the same rate, both during the 

 time they were heated (provided they were properly ad- 

 Owin'' to the j"sted) and afterwards, as they had done before. The cause 

 effect of the of this retardation appears to me to be, that the points of 

 point of con- contact of the different pieces, which compose the pendu- 

 tact. lum, are more closely connected after a little time, than they 



are at first; that is, those points of contact do, by the weight 

 of the ball, yield to each other in a small degree, until 

 they get a broader bearing. 

 Adv t " f '^'"'^ advantages of this pendulum are, 1st, that from its 

 thisijeiiduluni. simplicity it will never fail to have the desired effect. 2d1j', 

 That no extraordinary care is requisite in executing it. 

 3dly, That the compensation may be increased or diminished 

 with the'greatest ease, without stopping the clock more than 

 a minute, by itiakvng fast one of the screvrs -^hat keep th« 



rods 



