ON PENDULUMS, &C. g^ 



It is v»ell known that a bar of iron may be heated red a bar of iron 

 hot at one extremity without eiFecting any sensible change "^»y be red hot 

 ♦n the temperature of the, other extremity : would Mr. cold"\t" ihm 

 Boswell thence infer that no expansion whatever has other; 

 token place in the bar ? will he not rather admit a cer- 

 tain cxjiansion to have been produced in the heated end, — and would 

 and a gradual decrease of this expansion to have extended ^e^tcd ^^ ^^*^*^ 

 toward the cold extremity ? 



If the preceding effect be admitted to take place in a And so would 

 bar of metal, it must equally be admitted in every body Mr. Boswell's 

 which is susceptible of expansion by heat: Mr. Bqs- ^^^^ ° ^* 

 well's contrivance for rendering effective the compensa- 

 tions proposed by Crosthwaite or Pine must consequently 

 be nugatory, were the apparatus afhxed even to the side 

 of a mountain of granite in lieu of his octagonal pillar. 

 The other suggestions of Mr. Boswell, in which deal, objection to 

 mahogany, or metal is employed, I should apprehend to so"^e other of 

 be still less deserving of attention ; and 1 am incapable ^.^g^ 

 of perceiving the good effect which is likely to arise from 

 the filling the glass tube with semen lycopodii or sawdijst^ 

 or from the covering it with oiled silk. 



In hi« observations on a paper published in the Reper- Mr. B.'s ani- 

 tory of Arts, relative to Pine's and Crosthwaite's pen- rnadversionson 

 J 1 ^ L- 1 , x-u u ^ 1, 1 , Mr. Pine's pa- 



dulums, (whicli, by the bye, appear to me equally harsh per, not found- 



and unjust,) Mr. Boswell triumphs in his turn, with no ed on facts, 

 small satisfaction, on a supposed error of the author ; a 

 triumph which the preceding remarks will not so readily 

 authorize ; it may be even doubted whether the effect 

 would not have been greater in the solid plank than in the 

 simple rod. The cock through which the pendulum 

 spring passed in order to effect-the proposed compensa- 

 tion, I imagine to have been affixed to the plank by 

 screws: now, if from the imperfect conducting power Explanation. 

 of wood, with respect to caloric, we suppose the exterior 

 strata to expand from an increase of temperature, and 

 that the expansion of the interior strata gradually de- 

 crease, as in the afore-mentioned bar of iron, it is evi- 

 dent that the screws will turn, as it were, on their inte- 

 rior extremity, and form an angle with the axis of the 

 plank, supposing them to have been perpendicular to the 

 axis before the expansion took place j consequently the 



outer 



