560 Dr. J. H. Vincent on the Construction of a Mechanical 



Description of the Model. 



The model used to obtain the results given in fig. 2 is a 

 modification of thai: of Prof. Thomson. 



The cord is replaced by a loaded spiral spring, about two 

 metres long when kept under a small tension equal to the 

 weight of two or three grams. The spring was wound in one 

 piece on a cylinder about *75 centim. thick. The cylinder 

 was chosen by trial until the released spring was just large 

 enough to receive a number of leaden bullets (see fig. 3). 



Fig. 3. 



Each bullet was provided with a pair of hooks and cemented 

 into the hollow of the spring. One hook served to attach a 

 weight hanging by a thread, the other to fasten the bullet to 

 a long thread suspended from a plank fastened to the ceiling 

 (fig. 4). The spring was made of thin brass wire (No. 30, 

 Birm. W. G.). There were about 40 bullets inserted in the 

 spring, each being distant five turns from its neighbours. 



The length of the supporting threads was 271 centim., 

 while those attached to the lower system of weights were 

 56*5 centim. long. The hanging weights were about twice 

 as heavy as the bullets, the values of the constants being 



Mass of bullet = 13*8 grams. 

 a = 1*12 per sec. 

 b = *()6 per sec. 



The motion was in a horizontal plane transverse to the length 

 of the model. Without the hangers the model is suitable for 

 illustrating sound and light ; the motion in this case may be 

 made either longitudinal or transverse, and is so slow as to 

 be easily followed by the eye. 



