260 



THE POPULAR EDUCATOR. 





GEOMETRICAL PERSPECTIVE. XVI. 



THE PERSPECTIVE OP SHADOWS. 



WE now enter upon another division of our subject, Sciography, 

 a term which signifies the science of shadows. The rules for 

 their projection are founded, generally speaking, upon the same 

 principles as those for the projection of solids and planes ; yet, 



rays emanating from an artificial light, as a candle in a room, 

 are not parallel ; in this case they spread in all directions from 

 one common centre, upwards, downwards, and horizontally, BO 

 that under some conditions we shall have to introduce rules for 

 the construction of shadows subject to an artificial light, which 

 the pupil will find very different from anything that has been 

 previously placed before him. In working the problems relating 



V 



on account of many peculiarities arising from the causes which 

 originate them, in reference to the sources of light, together 

 with the various inclinations of surfaces upon which shadows 

 fall, there must necessarily be additional and distinctive rules 

 for their construction. We might point out a few of these 

 changes in cause and effect, but we think it better to leave them 

 until we come to special cases in which they are found, when we 

 can enter fully into all the particulars belonging to them. The 

 great source of light is the sun, whose rays may be said to be 

 parallel, on account Of its great distance from the earth. The 



to shadows, it will be necessary first to draw the perspective 

 representation cf the objects we shall have to introduce : an 

 explanation of this part of the work will not be repeated in 

 every case, as we trust our pupils are sufficiently competent to 

 do most of the work that is required previous to determining 

 the shadows. Should there be an exception to this regulation, 

 it will be when a question is proposed in which there may be 

 something unusual in the perspective of the object which has 

 not been considered before. 



The position of the sun, the source of light, may be first, 



