Update textbook.fr.md

12.temporary_ins/96.electromagnetism-in-media/20.reflexion-refraction-at-interfaces/10.boundary-conditions/10.main/textbook.fr.md

@@ -215,6 +215,8 @@ field, this condition can also be written:
 
 #### 3.2 - Reflection and transmission at normal incidence
 
+<br>
+
 We suppose that the *xy* plane at *z* = 0 is the boundary between
 medium 1 and medium 2. A plane wave of angular frequency *ω*
 travelling in medium 1 in the positive *z* direction and polarised
@@ -347,6 +349,8 @@ and
 
 #### 3.3 - Reflection and transmission at oblique incidence
 
+<br>
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 We now turn to the more general case of an oblique incidence at an
 arbitrary angle *θ~i~*. Before that we will need a few definitions and
 considerations.
@@ -465,6 +469,8 @@ sin *θ~t~* or
 
 #### 3.4 - Fresnel's laws & Brewster's angle
 
+<br>
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 From the previous section we can write the incident, reflected and
 transmitted waves as:
 
@@ -671,6 +677,8 @@ i.e. the reflected wave is totally reflected with a phase shift.
 
 #### 3.5 - Oblique incidence onto a perfect conductor
 
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 We consider now a linearly polarised plane wave travelling in a
 perfect dielec- tric making an oblique incidence onto a perfect
 conductor. The case of vacuum is trivially obtained by setting the