233 

 Some Experiments with a Simple Jolly Balance. 



Lynn B. MoMullen. 



lu presenting a paper of this kind before the Academy of Science I 

 think it is well to point out that the research work of the high school 

 teacher must be "re"search Avork indeed— must be research work back- 

 ward instead of forward. If I might be allowed to read you a parable 

 I shotild remind yoti that some fifty, or perhaps sixty, years ago our grand- 

 fathers came to Indiana to do research work of a bread-winning charac- 

 ter. But those grandparents had brothers, who, through necessity or 

 lack of years, were compelled to stay at 'iome and take care of the real 

 little folks. I take it that the same thing is true of the members of this 

 Academy. Some, usually those of the colleges, are able to do research 

 work. Others, iiarticularly those of the high schools, must expend their 

 energies in the perfecting of details. 



Those of us that rememlier our college course in Physics hold tlie old 

 Jolly balance, with which we wrestled, in much awe. Certainly no piece 

 of apparatus could be more perverse. The spring being stationary at the 

 top and entirely free at the bottom would take its time in coming to rest 

 and its distance from the meter stick gave parallax an excellent oppor- 

 tunity to do its worst. Further, as the spring stretched the table must 

 be moved, and the table was usually stuck. It is easy to see iioir that 

 the conversion of the Jolly balance from a rogue to a useful citizen de- 

 pended upon some device for stretching the .spring "up" from a stationary 

 bottom instead of '"down" from a stationary top. It is the purpose of this 

 paper to explain one such device and to present data showing the accuracy 

 that may be obtained by using it. 



The base of the balance is a Sapolio box 6x9xl2-in. mounted on level- 

 ing screws and weighted with a brick. To the front of the box is screwed 

 an upright standard fotir feet long. This standard is made by nailing to 

 the face of a piece of poplar i2x2-in. two strips %x^i>-iu. leaving a groove 

 between them 1-in. wide and V^-in. deep in which a meter stick may slide 

 freely. To the upper end of the meter stick is fastened a string which 

 runs over a pulley at the top of the standard. The other end of this 

 string is tied to the end of a large horizontal screw which runs through 

 the side of the box with sufficient frictioii to hold the meter stick in any 

 desired position. From the top of the meter stick at right angles to it 



