The Dlacatoplron. 129 



\vilh the window ; on the right hand lay some blank pa- 

 per, upon which a person may draw ; and between the two 

 place the Diacatopfron or transparent reflecting plate of 

 glass in its frame ; place the blind k at right angles with 

 the glass on the right hand, so that the drawing paper may 

 Jie in the broken shade, and a person looking through the 

 L'lass from the left side will observe the object exactly de- 

 signed ujion the paper. If the figure is not sufiiciently 

 distinct, you mav darken the bhnd by hanging a paper 

 upon it ; if it should darken too much, you place it a little 

 further from the glass. 



It is of much consequence that the proper degree of 

 shade should be thrown upon the paper ; lor, if it is too 

 dark, you will neither see distinctly the lines of the draw- 

 ing which you copy, nor the point of your pencil : if, on 

 the contrary, it is not sufficiently dark, you will work at 

 randon),_and the representation will be faint. In copying 

 after tins manner yon do not make use of any eye hole, 

 because the eye is easily kept in the proper direction, as the 

 drawing remains in its appro[)riate situation ; but in the 

 following e>:periments, where the objects are diminished 

 or magnified, whether a picture or prospects in perspec- 

 tive, the eye hole must be always used, since it is necessary 

 to look exactly and constantly at the same point of view. 



The dinnnishing of an object is effected by raising the 

 height of the table. Since the object placed on the left side 

 ot the glass is alwavs represented on the right side, although 

 the surface of (he tal)le should not be of an uniform height, 

 it will be found that, if you take a fixed point of view, the 

 object will be diminished the nearer the reflected image 

 ■approaches to 'ibis point, and will be magnified as the re- 

 flected and transmitted image is made to recede from the 

 eye. Or rather, the image will appear larger than the ob- 

 ject when it is removed further from the fixed eye than the 

 object itself, and vicevirsa. 



Tills may be setn clearer by fig. 5. The parallel lines 

 1, 2, 3, 4, 5, 6, 7, 8, represent the different heights of the 

 table. If now the line k were to be diminished, it would 

 be reduced -i- upon the table at 1, J- at 2, f at 3, and at 4 

 f, as is shown by the lines of sight where the parallel lines 

 intersect. 



Fig, 3. represents the Diacaloptron when the letter B 

 is diminished ^ ; the table with the paper is placed in the 

 fourth hole. 



Fig. 4. represents the magnifying of an object when the 

 table is on the left side. 



In both cases you must look at the object through the 

 Vol.39. No. 1G6. i'W'. 1812. I eye 



