On Pendulums, 



83 



Steel rod expands downwards the quicksilver expands up- 

 wards, and vice versa* The rate of the clock will show 

 whether the pendulum be over or under corrected ; conse- 

 quently by taking a little quicksilver out of the bob, or 

 adding a little, the compensation may be adjusted to the 

 utmost degree of exactness, and with very little trouble. 



It may be supposed that a pendulum cannot be adjusted 

 for heat and cold by the going of the clock, but the rate of 

 my clock shows that this supposition is not well founded ; 

 for when a wooden pendulum was attached to it, its rate 

 of going was affected merely by dryness and moisture; 

 but with a mercurial pendulum its rate was affected only by 

 heat and cold, the pendulum being a small matter under 

 corrected; but this variation in its rate during twelve 

 months was. very little more than one second per day, al- 

 though the temperature of the outward air did not vary 

 less, by Fahrenheit's scale, than 70 degrees. 



The following register of the going of this clock was 

 computed from the sun's transits over the meridian, ob- 

 served with a 3{ feet transit telescope. 



Lynn, July 16, 1810. E. WALKER. 



P. S. For an account of the greatest annual variation in 

 the daily rate of the transit clock at the Royal Observatory 

 for six years, see Phil. Mag. vol. xxxiv. p. 4. 



An Account of the Going of a Clock ivith a mercurial 

 Pendulum made by Mr, Barraud. 



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