Part 3

OF SPRINGS, FOUNTAINS, &c. 128

Of the Ascent of Vapour and the Formation of Clouds. Of the Formation and Fall of Rain, &c. Of the Formation of Springs. Of Rivers and Lakes. Of Fountains.

CONVERSATION XII.

PNEUMATICS.

ON THE MECHANICAL PROPERTIES OF AIR. 136

Of the Spring or Elasticity of the Air. Of the Weight of the Air. Experiments with the Air Pump. Of the Barometer. Mode of Weighing Air. Specific Gravity of Air. Of Pumps. Description of the Sucking Pump. Description of the Forcing Pump.

CONVERSATION XIII.

ON WIND AND SOUND. 146

Of Wind in General. Of the Trade Wind. Of the Periodical Trade Winds. Of the Aerial Tides. Of Sound in General. Of Sonorous Bodies. Of Musical Sounds. Of Concord or Harmony, and Melody.

CONVERSATION XIV.

ON OPTICS. 157

Of Luminous, Transparent, and Opaque Bodies. Of the Radiation of Light. Of Shadows. Of the Reflection of Light. Opaque Bodies seen only by Reflected Light. Vision Explained. Camera Obscura. Image of Objects on the Retina.

CONVERSATION XV.

OPTICS--continued.

OF THE ANGLE OF VISION, AND REFLECTION OF MIRRORS. 168

Angle of Vision. Reflection of Plain Mirrors. Reflection of Convex Mirrors. Reflection of Concave Mirrors.

CONVERSATION XVI.

ON REFRACTION AND COLOURS. 179

Transmission of Light by Transparent Bodies. Refraction. Refraction by the Atmosphere. Refraction by a Lens. Refraction by the Prism. Of Colour from the Rays of Light. Of the Colours of Bodies.

CONVERSATION XVII.

ON THE STRUCTURE OF THE EYE, AND OPTICAL INSTRUMENTS. 195

Description of the Eye. Of the Image on the Retina. Refraction by the Humours of the Eye. Of the use of Spectacles. Of the Single Microscope. Of the Double Microscope. Of the Solar Microscope. Magic Lanthorn. Refracting Telescope. Reflecting Telescope.

GLOSSARY, 205

CONVERSATION I.

ON GENERAL PROPERTIES OF BODIES.

INTRODUCTION. GENERAL PROPERTIES OF BODIES. IMPENETRABILITY. EXTENSION. FIGURE. DIVISIBILITY. INERTIA. ATTRACTION. ATTRACTION 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 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 inquired 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 all other things, should be able to support itself.