136 



THE POPULAR EDUCATOR. 



Pig. 112. 



lc o ; the same with the upper slope. The reason why neither 

 of these slopes are seen in the reflection is because the point 

 p coincides with g (Fig. 115) on the picture plane: therefore the 

 Bame line, F 0, represents both extremities of the slope. If the 

 slope B had had a greater elevation that is, had it been at a 

 greater angle 

 then the 

 upper extre- 

 mity would 

 have admitted 

 a line to s 2 , 

 and conse- 

 quently would 

 have cut the 

 picture plane 

 EE 1 at a higher 

 point than g; 

 and that point 

 of intersection 

 would have 

 been shown 

 below g in the 

 reflection. And 

 also for rea- 

 sons given 

 above, we see 

 parts reflected 

 which are not 

 visible in the 

 objects them- 

 selves. Figs. 

 117 and 118 

 will satisfy the 

 mind upon 

 this point. 



The subject is a cottage on a bank with a large notice-board in 

 front of it. The profile view (Fig. 117) will explain the dis- 

 tance of the board from the cottage, and this will account for 

 the great difference between the details of the projection A and 

 the reflection B in Fig. 118. If the pupil fail not to work 

 out this problem 

 also (of which, 

 being constructed 

 by the same rules 

 as the former, we 

 give no detailed P P 

 explanation, but 

 prefer leaving it 

 as it is, for an 

 exercise), he will 

 more readily un- 

 derstand it, and 

 the method of 

 construction also; 

 remembering that 

 the visual rays 

 drawn from every 

 important point of 

 the whole passing 

 through P P (the 

 picture plane) de- 

 termine the points 

 to be transferred 

 to the correspond- 

 ing plane on the 

 left in Fig. 118. 

 We remark that 

 the notice board 

 covers part of the 

 roof in the pro- 

 jection A, whilst 

 it is clear of the 



roof in the reflection B. Also compare the chimneys in both 

 cases with respect to their apparent position with the board. 

 In the reflection B the sills of the windows are on a line with 

 the base of the post, and the thresholds of the doors cannot 

 be seen because they are hidden by the bank. There are 

 other differences, which the pupil will be able to discover 



for himself. The same may be satisfactorily proved witt 

 regard to clouds. It is common, also, in their cases to see 

 brilliant reflections of light clouds on the water, when to the 

 eye there is nothing to account for them. These reflections 

 are invariably caused by light clouds which are hidden from 



view behind 

 other clouds, 

 the reflections 

 affording us 

 the only evi- 

 dence of their 

 existence. 

 Why is this ? 

 And where is 

 the root of the 

 mistake that 

 is so frequent- 

 ly made, that, 

 without excep- . 

 tion, whatever 

 we paint above 

 the water must 

 be necessarily 

 repeated by 

 its reflection? 

 It is simply 

 this, that 

 many treat 

 the whole 

 view, sky and 

 all included, 

 as one single 

 plane, never 

 thinking there 

 are parts more 



| remote than others, and consequently many are reflected which 

 are shut out from the eye by intervening objects. 



Water not only receives reflections, but, conditionally, is 

 capable of receiving shadows. If the water is perfectly clear, 

 no shadows occur, and the reflections are more or lesp vivid in 



proportion as the 

 water is more or 

 less impregnated 

 with colouring 

 matter, say clay, 

 or as rivers gene- 

 rally appear after 

 heavy rains. Then 

 the strength of 

 the reflections and 

 shadows alternate 

 in proportion to 

 the clearness or 

 opacity of the 

 water. When it 

 is very thick and 

 muddy, the sha- 

 dows of objects 

 are cast as forcibly 

 upon the surface 

 as they are on a 

 road ; and as it 

 becomes clearer, 

 the reflections be- 

 come more bril- 

 liant and the\ 

 shadows weaker : 

 the earthy par- 

 tides mingled with 

 the water receive 

 the shadow, not 

 the water itself. 



In perfectly clear water the light passes through the water 

 itself, as through a piece of glass, lighting up the bed of the 

 river, so that we are able to distinguish readily the stones, 

 weeds, sh, and whatever else may be at the bottom ; then the 

 shadow which falls upon the water sinks as it were, and is seea 

 at the bottom only. 



