136 Mr. Charles Tomlinson, on the Curved Figures 



the radii of a star on the smaller disk when viewed through 

 a slit in the larger disk, and both revolving, were curved. 

 The nature and symmetry of these curves are dependent on 

 several conditions, which may he thus stated : 



1. The relative sizes of the disks. 



2. The relative velocities of the disks. 



3. The respective rotations being in the same, or in oppo- 

 site directions. 



4. The situation of the slit. 



5. The part of the slit to which the eye is applied. 



The great variations produced by changes in these con- 

 ditions render it impossible to convey a correct idea of the 

 curves, unless we adhere to one ratio of proportion in each 

 of the above particulars, and to effect this in the completest 

 manner, the following mode of observation was adopted : 



Instead of employing two rotating disks, the slit is made 

 in the disk, which is the object of experiment, and the eye, 

 placed behind the disk, views through the slit the image of 

 the rotating figure reflected in a stationary plane mirror, 

 placed in front of the disk, within about two feet. 



Thus, by considering the revolving image as a second re- 

 volving disk, the following conditions are fulfilled : 



1. The two disks are of equal size. 



2. They rotate with equal velocities. 



3. They rotate in the same direction. 



These three data being thus constant, the effect of varia- 

 tion in the fourth and fifth will now be described. 



The disk. 



Fie:. 1. 



is covered with a star, consisting of eight black and 

 eight red radial bands. The slit A. B. occupies nearly a 



