Conversations on Natural Philosophy: In which the Elements of that Science are Familiarly Explained and Adapted to the Comprehension of Young Pupils : Illustrated with Plates

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J.Y. Humphreys, 1821 - 311 páginas
 

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Página 102 - Now came still evening on, and twilight gray Had in her sober livery all things clad ; Silence accompanied ; for beast and bird, They to their grassy couch, these to their nests Were slunk, all but the wakeful nightingale ; She all night long her amorous descant sung...
Página 102 - The starry host, rode brightest, till the moon, Rising in clouded majesty, at length, Apparent queen, unveil'd her peerless light, And o'er the dark her silver mantle threw.
Página 77 - ... time that the axle describes a small one, therefore the power is increased in the same proportion as the circumference of the wheel is greater than that of the axle. If the...
Página 230 - The construction of the eye is so admirable, that it is capable of adapting itself, more or less, to the circumstances in which it is placed. In a faint light the pupil dilates so as to receive an additional quantity of rays, and in a strong light it contracts, in order to prevent the intensity of the light from injuring the optic nerve.
Página 49 - B it receives in return a blow equal to that which it gave, but in a contrary direction, and its motion is thereby stopped, or rather, given to B. Therefore, when a body strikes against another, the quantity of motion communicated to the second body...
Página 218 - ... the white rays of the sun are composed of coloured rays, which when blended together, appear colourless or white. Sir Isaac Newton, to whom we are indebted for the most important discoveries respecting light and colours, was the first who divided a white ray of light, and found it to consist of an assemblage of coloured rays, which formed an image upon the wall, such as is exhibited, in which are displayed the following series of colours — red, orange, yellow, green, blue, indigo, and violet.
Página 64 - The curve-line which the ball has described, is called in geometry, a parabola; but when the ball is thrown perpendicularly upwards, it will descend perpendicularly ; because the force of projection, and that of gravity, are in the same line of direction. We have noticed the centres of magnitude, and of motion ; but I have not yet explained to you what is meant by the centre of gravity ; it is that point in a body, about which all the parts exactly balance each other ; if, therefore, that point is...
Página 140 - I hope, thoroughly impressed upon your memory, by the conversation we have subsequently had on astronomy. It will now be necessary for me to give you some account of the mechanical properties of fluids, a science which is called hydrostaticS. A fluid is a substance which yields to the slightest pressure. If you dip your hand into a basin of water, you are scarcely sensible of meeting with any resistance.
Página 117 - We shall now explain the variation of the seasons, and the difference of the length of the days and nights in those seasons — both effects resulting from the same cause.
Página 147 - All the metals expand by heat, and condense by cold. A piece of lead, let us say a cubic inch, for instance, would have less specific gravity in summer than in winter; for it would be more dense in the latter season. CAROLINE. • But, Mrs. B., if you compare the weight of equal quantities of different bodies, they will all be alike. You know the old saying, that a pound of feathers is as heavy as a pound of lead ! MRS.

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