A Treatise of Mathematical Instruments, including most of the instruments employed in Drawing; for assisting the vision; in Surveying and Levelling, in practical Astronomy and for measuring the Angles of Crystals

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John Weale, 1849 - 183 sider
 

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Side 72 - ... that the sine of the angle of refraction bears a constant ratio to the sine of the angle of incidence...
Side 104 - In looking through a telescope a considerable field of view is embraced ; but the measurements indicated by any instrument, of which the telescope may form a part, will only have reference to one particular point in this field of view, which particular point is considered as the centre of this field of view. We must therefore place some fixed point...
Side 78 - When you have proved that the three angles of every triangle are equal to two right angles...
Side 107 - ... is out of adjustment, and requires correcting. The end to which the bubble retires must then be noticed, and the bubble made to return one-half the distance by turning the parallel plate screws, and the other half by turning the capstan-headed screw at the end of the bubble tube. The telescope must now again be reversed, and the operation...
Side 110 - The best constructed levelling staff* consists of three parts, which pack together for carriage in a neat manner, and, when opened out for use, form a staff seventeen feet long, jointed together something after the manner of a fishing-rod. The whole length is divided into hundredths of a foot, alternately coloured black and white, and occupying half the breadth of the staff; but for distinctness the lines denoting tenths of feet are continued the whole breadth, every half foot or five-tenths being...
Side 178 - Place the crystal which is to be measured on the table, resting on one of the two planes whose inclination is required, and with the edge at which those planes meet, nearest and parallel to the window.
Side 131 - Adjustments of the telescope : viz., the adjustment for parallax. for collimation. 2. Adjustment of the horizontal limb : viz., to set the levels on the horizontal limb to indicate the verticality of the azimuthal axis.
Side 179 - Now turn the graduated circle, by means of the handle, b, until the image of the bar, reflected from the second plane, is also observed to coincide with the same line below. In this state of the instrument the vernier at c will indicate the degrees and minutes at which the two planes are inclined to each other. " The accuracy of the measurements taken with this instrument will depend upon the precision with which the image cf the bar, reflected successively from both planes, is made to appear to...
Side 157 - Repeat the operation till the bubble retains the same position in both positions of the level, and the axis will be horizontal. To adjust the Line of Collimation in Azimuth. — Direct the telescope to some distant, small, and well-defined object, and bisect it by one extremity of the middle vertical wire, giving the telescope the azimuthal motion necessary for this purpose by turning the screw S. By elevating or depressing the telescope, examine whether the object is bisected by every part of the...
Side 99 - ... all his arrows. Ten chains, or 1000 links, have now been measured, and, this measurement having been noted in the field book, the follower returns the ten arrows to the leader, and the same operations are repeated. When the leader arrives at the end of the line, the number of arrows in the...

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