4-0 iNIr. Sijuire on Compensating Penditldnis. 



breadth and thickness ; and after cutting it to the required 

 length, let the surface be well coated with copal varnish, and 

 the ends dipped in melted sealing-wax, to prevent the least 

 moisture penetrating the wood, which is of the utmost conse- 

 quence to the accuracy of the pendulum in its simple state. 

 But still, if, after all, the pendulum should be found to be in 

 some degree affected by the changes of the atmosphere, we 

 happily have in the nature of wood a remedy at hand for this 

 inconvenience. 



As the expansion and contraction of deal is much greater 

 across than in the direction of the grain, cut a small block 

 from the waste piece, equal in length to the width of the pen- 

 dulum rod, and of the same thickness, whicli may be about 

 •78 of an inch by '37 respectively; let this block be placed with 

 its grain at right angles with that of the rod, having its lower 

 side resting on the nut at the bottom of the pendulum, and its 

 upper side supporting the bob, and which, if judiciously placed 

 behind the front plate, will not only be nearly out of sight, 

 but may be so contrived as equally to compensate for the up- 

 per part of the screw, and the small piece of spring on which 

 the pendulum is hung. Experiment proves that with deal the 

 block need not be more than half an inch in width for the 

 compensation of a seconds pendulum rod of the same material. 



It is almost unnecessary to remark, that the compensating 

 block should be from a part of the same rod as the pendulum 

 to which it is applied, and also be in every other respect simi- 

 lar as to previous preparation, &c. 



I remain, gentlemen, yours, &c, 

 Epping, Dec. 15, 1824. Thomas Souire. 



P.S. I take this opportunity of returning my best thanks 

 to Dr. Burney and Mr. Veall, for their ready compliance 

 with my request relative to the situation of their meteorolo- 

 gical instruments. 



I should like very much to see an account of some well 

 conducted experiments on the expansion and contraction of 

 wood, made under different degrees of temperature and dry- 

 ness, with the ratio of the same across and in the direction 

 of the grain ; at the same time pointing out the best and most 

 expeditious methods of entirely destroying this variable pro- 

 perty of wood. T. S. 



[We think it may be acceptable to our readers if we subjoin to tiie above 

 communication witii which Mr. Squire has favoured us, some extracts re- 

 lating to tlic lis;- of deal foi' peiuhiliim rvxls from Mr. Haily's valniililt- Paper 



