t 487 ] 



XLV. Petrovitclis Apparatus for integrating Differential 

 Equations of the First Order. By W. A. Price *. 



M MICHEL PETROYITCH, Professor of Mathematics 

 • at Belgrade, has described in a recent number of 

 the American Journal of Mathematics (vol. xxii. No. 1) an 

 interesting instrument for integrating differential equations 

 of the form X dx + Ydy = 0. 



Two curved templates, B, C (see fig. 1), made from thick 

 plank are plunged into a rectangular tank of water. To B is 

 attached a pointer Q, and to C a pointer R. A pencil P is 



Fig. 1. 



attached by a vertical rod to an index A, which is placed at 

 the surface of the water. AP, BQ, OR can be moved verti- 

 cally but not horizontally. The lengths AP, BQ, OR are 

 drawn for convenience of the same length, /, though this is not 

 essential. A board is moved horizontally behind PQR, and 

 the templates B, are moved in and out of the water by 

 keeping Q, R upon curves previously drawn on the board. 



* Communicated by the Author. 



