The Prosecution at Bow Street of Dr Slade , The Spirit Medium Above , counsel for the prosecution , cross examining the prisoner ' I wonder whether the spirits will appear in Court today ' . Below , Professor E Ray Lankester , giving evidence : ' I watched you writing on the slate . You are a scoundrel and an imposter . ' Mr Maskelyne demonstrated in Court how writing on the slate had been invisibly manipulated by a well trained expert . 1876