Boyle, than I do in all the abstractions, and reduplications, of the most subtle metaphysicians. SECT. X. XXXVII. It is certainly and indispensably necessary, to make experimental observations with the most exquisite attention, in order to avoid our being deceived by them, as our forefathers have been, and as many people are at this day; who, confiding in a superficial and careless experiment, have precipitated their conclusions, and without giving themselves time to reflect, have deduced consequences, from the first information of their senses. From the ascent of the water in the pump, by considering the thing inattentively, was inferred the repugnance of nature to a vacuum. To what labours did Torrizeli, Pascal, and other sublime geniuses submit, what a variety of experiments did they make, and with what ingenuity did they combine and compare them, in order to undeceive the world, and convince mankind, that the true cause of this phenomenon was the weight of the air! XXXVIII. From the flame flying upwards, was inferred the chimerical region of fire, immediately adjoining to the heaven of the moon. In our essay on Physical Paradoxes, we related the ingenious experiment with which my Lord Bacon proved, that the flame did not ascend from any natural propensity it had to fly upwards, but because it was compelled to it, by the lateral pressure of the air. XXXIX. I was once in conversation with some school philosophers, and our discourse happening to turn upon physical matters, I took occasion to propose a question to them, which was, whether cold water (and the same may be said of every other liquid) was more subtil and penetrating than hot, which it seemed evidently to be, by the following experiment, that when we poured iced water to drink in summer time into a glass, we perceived the glass wet and moist on the outside, which had the appearance of the water having transuded through the pores of the glass; and as this did not happen when the water was luke warm, or in a temperate state, it was inferred that such water, was not so subtil and thin as cold. As the bystanders seemed converts to the force of the before-named experiment, it gave me a good deal of trouble, to undeceive and convince them of their mistake, although at length I accomplished doing it, by making it evident to them by various most clear experiments, that the moisture which adhered to the outside of the glass, did not transude through its pores, but that it consisted of the coagulated vapours, of the circumambient air, which being in a warm state, condensed and were converted into water, upon their coming in contact with any very cold body, and that they became more condensed the less porous this body was. For this reason, the vapours that are raised by fire, condense as soon as they come to the head of the alembick; and for the same, if we breathe upon a bright iron bar, or any other metallic body, that has