Consider the following statements in respect of arched construction made of voussoirs: 
1) The superimposed load is transferred to the sidewalls only by the strength of cohesion of the mortar between the voussoirs 
2) The arch may fail under crushing when the compressive stress or thrust in it exceeds the safe crushing strength of the voussoir material 
3) Every element in the arch is subjected to compression only 
4) Failure of the arch due to the sliding of any voussoir past the adjacent one due to transverse shear can be avoided by reducing the height of the voussoirs 
Which of the above statements are correct?