With his next letter, he sends her a gift of books, and begs her to accept it, as a small mark of his esteem and friendship, and the gift is accompanied with more specific advice as to the manner in which she was to prosecute her studies, and obtain the benefit of his knowledge and counsel. When he writes again, his letter discloses the fact that a brisk interchange of ideas had been actually established between them. "'Tis a very sensible Question you ask," he says, "how the Air can affect the Barometer, when its Opening appears covered with Wood?" And her observation on what she had lately read concerning insects is very just and solid too, he remarks. The question he has no difficulty in answering, and the observation on insects leads to some agreeable statements about the silk-worm, the bee, the cochineal and the Spanish fly, and finally to an interesting account of the way in which the great Swedish naturalist, Linnaeus had been successfully called in by his King to suggest some means of checking the ravages of the worm that was doing such injury to the Swedish ships. Nor was all this mellifluous information imparted without a timely caution. There is, however [he concluded], a prudent Moderation to be used in Studies of this kind. The Knowledge of Nature may be ornamental, and it may be useful; but if, to attain an Eminence in that, we neglect the Knowledge and Practice of essential Duties, we deserve Reprehension. For there is no Rank in Natural Knowledge of equal Dignity and Importance with that of being a good Parent, a good Child, a good Husband or Wife, a good Neighbour or Friend, a good Subject or Citizen, that is, in short, a good Christian. Nicholas Gimcrack, therefore, who neglected the Care of his Family, to Pursue Butterflies, was a just Object of Ridicule, and we must give him up as fair Game to the satyrist. A later letter is an amusing illustration of the manner in which he occasionally reminded his pupil that she must not take herself and Philosophy too seriously. Polly was at the time at the famous Wells of Bristol about which so much of the social pageantry of the eighteenth century centred. Your first Question, _What is the Reason the Water at this place, tho' cold at the Spring, becomes warm by Pumping?_ it will be most prudent in me to forbear attempting to answer [he said], till, by a more circumstantial account, you assure me of the Fact. I own I should expect that Operation to warm, not so much the Water pump'd, as the Person pumping. The Rubbing of dry Solids together has been long observ'd to produce Heat; but the like Effect has never yet, that I have heard, been produc'd by the mere Agitation of Fluids, or Friction of Fluids with Solids.