The personification of Justice carries a scale in which the evidence is balanced against the truth, which symbolizes the impartiality of the law >> http://tinyurl.com/2hgnlq.
To be cast into the other pan of the scale = taken from one pan in the scale and put into the other.
More context is really needed to decide exactly what is being meant.
To be cast on the other pan of the scale. 
Linear Mode
