“…it is not the duty of the judge to invite the jury to speculate as to provocative incidents, of which there is no evidence and which cannot be reasonably inferred from the evidence. The duty of the jury to give the accused the benefit of the doubt is a duty which they should discharge having regard to the material before them, for it is on the evidence, and the evidence alone, that the prisoner is being tried, and it would only lead to confusion and possible injustice if either judge or jury went outside it.”