No. 2, An Experiment to Show the Expansion of Wood. 5 1 



instrument by Wm. J. Young, the mathematical instru- 

 ment maker. 



To test the expansion the wooden rod was first plac- 

 ed outside the window with a thermometer by the side 

 ol it, and left there until it was supposed to be of the 

 same temperature as the air; it was then taken in and 

 set in place under the index. Immediately, on look- 

 ing through the microscope, the point of the index was 

 seen moving slowly up the scale, showing not only 

 that wood did expand, but that it did so almost instant- 

 ly on being brought into the warm room. The heat of 

 the room was shown by two thermometers, hung, one 

 at the top, and the other at the bottom of the rod. In 

 a few minutes, when the point of the index became 

 stationary, its position on the scale was carefully noted, 

 as its former position had been before, as well as the 

 readings of the thermometers out-doors and in. The 

 difference between that without and the mean of the 

 two within was assumed as the increase in temperature; 

 and from the difference of the two readings on the 

 scale the corresponding increase in the length of the 

 rod was easily computed. 



The distance of the point of the index from the 

 needle or centre of motion being 14.6 times as great 

 as the point resting on the rod from the same centre, 

 it must move 14.6 times as fast and as far. Then di- 

 viding the space passed over by the index on the scale 

 should give the actual lengthening of the rod. 



In one observation, for example, the outside ther- 

 mometer marked 32 , and the two inside 6i° and 57 , 

 giving a mean 59 , and a difference of 27 . The read- 

 ings on the scale were .540 and .569, showing a rise 

 of .029 of an inch for the 27 increase of temperature. 

 As the change of temperature was different at differ- 

 ent times, the result of each observation was increased 

 or diminished to correspond to a change of 30 . In 

 this case it was done by adding 1-9 to the result for 

 27 , which gave .0322 of an inch, and this fraction divi- 

 ded by 14.6 gave .0022, or a little more than 1-500 of an 

 inch as the entire expansion of a four foot rod for 30 



