Around Christmas 1921, 16-year-old Vera Howley began to take singing lessons from Owen Richard Williams, the choirmaster of a local Presbyterian church. He had an odd way of working:
On the occasion of the second singing lesson on January 17 the appellant said that she was not singing as she should and was not getting her notes properly and told her to lie down on a settee. He then removed a portion of her clothing and placed upon the lower part of her body an instrument — which was in the nature of an aneroid barometer and according to the evidence was not in working order and would not in any event have been affected by the breathing of the girl — and then told her to take a deep breath three times. He looked at the instrument and purported to write something in a book. He then dropped on to her and proceeded to have sexual intercourse with her. She said: ‘What are you going to do?’ He said: ‘It is quite all right; do not worry. I am going to make an air passage. This is my method of training. Your breathing is not quite right and I have to make an air passage to make it right. Your parents know all about it, it has all been arranged; before God, Vera, it is quite right. I will not do you any harm.’ The girl made no resistance, as she believed what he told her and did not know that what he did was wrong — nor did she know that he was having sexual intercourse with her. The appellant had sexual intercourse with the girl a second time on April 28 in similar circumstances.
Vera told her parents, and Williams was tried at the Liverpool Assizes. He argued that she’d given consent; the court ruled that she’d consented to what she thought was a medical or surgical operation, not intercourse. Williams served 7 years for rape and 12 months for indecent assault.
(King v. Williams  1 K.B. 340. From Ralph Slovenko, Tragicomedy in Court Opinions, 1973.)