No. 2. An Experiment to Show the Expansion of Wood. 49 



AN EXPERIMENT TO SHOW THE EXPANSION OF WOOD. 



BY MR. HUGH D. VAIL. 



A number of years ago I concluded to try the exper- 

 iment of compensating an old fashioned clock 

 by using a wooden rod for the pendulum with a lead 

 pipe for the bob. 



To do this it became necessary to know the rela- 

 tive expansion of the two materials by heat. That of 

 lead was readily found in scientific tables; but none of 

 these gave that of wood, and it even seemed a question 

 whether wood expanded or contracted by heat. I 

 therefore decided to test it myself. I procured some 

 strips of straight grained, well seasoned white pine, 

 and also of Spanish cedar, the kind ordinarily used in 

 Philadelphia for the Surveyors' measuring rods. These 

 were cut exactly of the same dimensions — an inch 

 wide, three-fourth of an inch thick, and four feet long. 

 As the expansion, if any, was likely to be extremely 

 small, it was necessary to obviate all tendency to bend 

 or twist. To do this I slit the rods flatwise with a fine 

 saw, into exactly two equal parts, and then, after plan- 

 ing them smooth, I turned the outside of one part 

 against the inside of the other and screwed them firm- 

 ly together again. In this position the natural tenden- 

 cies of the two halves to warp or twist, being equal and 

 in opposite directions, neutralized each other. 



The apparatus for testing their expansion was a very 

 simple contrivance that I fitted up against the side of 

 a book case standing near a window. A small steel 

 point (B) fastened in this, about a foot from the floor, 

 with the point upwards, formed the support for the rod 

 when standing upright against the side of the book 

 case. To hold the rod in place small pieces of wood 

 were fastened to the case on both sides of it, near the 



