Transmission of Light by Transparent Bodies.- Refrac- Description of the Eye. Of the Image formed on the Refraction of the Humours of the Eye.- Of the Use of Spectacles. Of the single Microscope. Of the Double Microscope. Of the Solar Micro- scope.- Magic Lanthorn. — Refracting Telescope. Achromatic Telescope. Reflecting Telescope. - TRACTION OF COHESION.-DENSITY.-RARITY.HEAT. ATTRACTION OF GRAVITATION. EMILY. I MUST request your assistance, my dear Mrs. B., in a charge which I have lately undertaken: it is, that of instructing my youngest sister; a task, which I find proves more difficult than I had at first imagined. I can teach her the common routine of children's lessons tolerably well; but she is such an inquisitive little creature, that she is not satisfied without an explanation of every difficulty that occurs to her, and frequently asks me questions which I am at a loss to answer. This morning, for instance, when I had explained to her that the world B was round like a ball, instead of being flat, as she had supposed, and that it was surrounded by the air, she asked me what supported it. I told her that it required no support; she then enquired why it did not fall as every thing else did. This, I confess, perplexed me: for I had myself been satisfied with learning that the world floated in the air, without considering how unnatural it was that so heavy a body, bearing the weight of so many things on its surface, should support itself. MRS. B. I make no doubt, my dear, but that I shall be able to explain this difficulty to you; but I believe that it would be almost impossible to render it intelligible to the comprehension of so young a child as your sister Sophia. You, who are now in your thirteenth year, may, I think, with great propriety, learn not only the cause of this particular fact, but acquire a general knowledge of the laws by which the natural world is governed. EMILY. Of all things, it is what I should most like to learn; but I was afraid it was too difficult a study, even at my age. MRS. B. Not when familiarly explained: if you have patience to attend, I will most willingly give you all the information in my power. You may, per |