622 



REPORT — 1898. 



obtained on any ordinary board, and fig. 6 shows a side view of one of a 

 pair of ratchet wheels which could be employed so as to do away with 

 entirely the necessity for even one continuous axle. The ratchet wheels 

 on either side are successively moved an equal distance by adjusting the 

 position of two stops, one of which is shown in figs. 4 and 5. Hence for 

 each successive position, the two pitch circles on the respective sheets of 

 cardboard travel an equal distance, just as if they were really rolling 

 upon each other. ^ 



Fig. 6. 



Still even with this appliance circles are often required of incon- 

 venient size, while for drawing hypocycloidal and other curves the fixed 

 centre of one moving surface has its position above the moving portion of 

 the other. 



An arrangement, shown in fig. 1, of sliding bars, had been adopted to 

 overcome this difficulty, but it was obvious that the use of actual centres 

 of rotation were often very inconvenient, since it limited the size of the 

 rolling pitch circles, and what is believed to be an entirely new method of 

 obtaining circles of any size was devised, which does not involve the use 

 of an actual centre at all. This method may be briefly described as the 

 ase of two pairs of edge runners, the intersection of the axis of each pair 



