a smooth or polished surface, and is very cold, the vapour we breathe from our mouths, when it comes in contact with that body, will condense, and adhere to it; and it is also for the same reason, that in frosty nights, we see the inside of the glass of windows moist, when they are dry without, which appearance, I have known surprise many people, who thought that that humidity was a portion of the external air, which had penetrated through the glass; and it is likewise for the same reason, that our breath, and the breath of other animals, is visible in cold weather, it being then sufficiently condensed by the circumambient air, to make it become apparent. But the most convincing argument I made use of in the dispute, and which I advanced as a conclusive one, was, that if you covered the exterior superficies of the glass with paper, there would not the least moisture adhere to it, in the whole course of a frosty night, and it is clear that the paper is not impenetrable to moisture, but can only prevent the external air, from coming immediately in contact with the glass. XL. As it relates to the subject of the impenetrability of glass by liquids, I cannot forbear in this place taking notice of another very common error, which has originated from drawing conclusions hastily from experiments, without making proper reflexions on them. It is generally believed, that the zest of the rind of a lemon penetrates through glass, which opinion is founded on the persuasion, that if you press out the zest on the outside of a glass, the liquor that is within will taste of it. I concluding this penetration to be impossible, after meditating upon the matter, easily discovered the cause of this error; which is as follows, upon pressing out the zest, some of the particles are apt to fly and rest on the edges of the glass or very near it, and adhere to that part, which in drinking the lip is applied to; and thus the palate perceives the taste of the zest, which is communicated to it, from the edge of the glass. To determine whether this was not the case, I squeezed some of the zest in the ordinary way against the outside of the glass, and then turning it half round, applied my lips to the opposite side, and did not perceive the least taste or flavour of the zest of the lemon. And it will happen the same to any one, who will give himself the trouble to make the same experiment. SECT. XI.