I'm sorry to have to disagree with everyone

, but in that social/historical/English context 'being on easy terms in the house' meant that he was free to go where he pleased on his own, without being accompanied by a maid or butler - he went up to the laboratory on his own. Even today, someone who is about to leave (in polite society) has to be 'shown to the door' - but probably by the host rather than a servant. If the host is on more familiar terms with a guest, he'll say something lke 'You can find your own way out, can't you?' - a relic of the old social belief that guests shouldn't wander about unaccompanied
b