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altitude angle of incidence angle of refraction apparent diameter apparent magnitude appear axis centre centripetal force circle colours concave conductor conjunction consequently converge convex lens degrees described disk diverge drop earth eclipse ecliptick electrick electrified equal equator eye-glass fall fluid focal distance focus force given glass greater Hence horizon horizontal parallax inches incident ray inferior conjunction inferior planets inversely Jupiter latitude less libration longitude magnet magnetick mean anomaly mercury meridian mirror moon moon's motion move nearer nodes object-glass oblique observation opposite optick orbit parallax parallel rays particles passing perpendicular planet pole PROP radiant radius ratio reflected ray refraction revolution revolve right angles right ascension right line satellite Schol semidiameter shadow shewn side sine spectator square star sun's supposed surface syzygies tangent telescope triangle tube velocity Venus vessel weight whence
Page 346 - It is very probable that the great stratum called the milky way, is that in which the sun is placed, though perhaps not in the very centre of its thickness.
Page 226 - Every Ray of Light in its passage through any refracting Surface is put into a certain transient Constitution or State, which in the progress of the Ray returns at equal Intervals, and disposes the Ray at every return to be easily transmitted through the next refracting Surface, and between the returns to be easily reflected by it.
Page 348 - As, by the former supposition, the luminous central point must far exceed the standard of what we call a star, so, in the latter, the shining matter about the centre will be much too small to come under the same denomination; we therefore either have a central body which is not a star, or have a star which is involved in a shining fluid, of a nature totally unknown to us.
Page 346 - ... great combination with numberless others; and in order to investigate what will be the appearances from this contracted situation, let us begin with the naked eye. The stars of the first magnitude being in all probability the nearest, will furnish us with a step to begin our scale; setting off. therefore, with the distance of Sirius or Arcturus, for instance, as unity, we will at present suppose, that those of the second magnitude are at double, and those of the third at treble the distance,...
Page 180 - This amounts to the same with saying, that, in the case before us, the sine of the angle of incidence is to the sine of the angle of refraction in a given ratio.
Page 346 - ... to be the whole contents of the heavens. Allowing him now the use of a common telescope, he begins to suspect that all the milkiness of the bright path which surrounds the sphere may be owing to stars. He perceives a few clusters of them in various parts of the heavens, and finds also that there...
Page 292 - The appearance of what I have called the actual fire or eruption of a volcano, exactly resembled a small piece of burning charcoal, when it is covered by a Very thin coat of white ashes, which frequently adhere to it when it has been some time ignited ; and it had a degree of brightness, about as strong as that with which such a coal would be seen to glow in faint day-light.
Page 165 - Let a portion of a beam of light be intercepted by any body : the shadow of that body will be bounded by right lines passing from the luminous body, and meeting the lines which terminate the opaque body. 2. A ray of light, passing through a small orifice into a dark room, proceeds in a straight line. 3. Rays will not pass through a bended tube.
Page 346 - We will now retreat to our own retired station in one of the planets attending a star in the great combination with numberless others; and in order to investigate what will be the appearances from this contracted situation, let us begin with the naked eye. The stars of the first magnitude, being, in all probability, the nearest, will furnish us with a step to begin our scale ; setting off, therefore, with the distance of Sirius...