## A Treatise on 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 : in which Their Construction, and the Methods of Testing, Adjusting, and Using Them, are Concisely Explained with Corrections |

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accuracy adjustment altitude axis azimuth beam compasses bisected breadth bubble called chain chromatic dispersion clamp coincide colatitude compasses construction correction cross wires described diaphragm distinct vision Ditto ditto divided drawing edge equal error extent will reach eye-piece feet figure focal length given number gnomonic projection goniometer horizontal inches index glass instru instrument intersection latitude lens lenses limb line of collimation line of numbers line of sines logarithmic marked means measured ment meridian microscope number of degrees object object-glass observed paper parallax parallel plate pass perpendicular placed plane position primary divisions prism protractor quarter girt radius rays reading reflected image reflector refracting refracting telescopes represent right ascension round secants sector sextant side slider sliding speculum spherical aberration spirit level square station strument subdivisions tangents telescope theodolite transit transverse distance triangle tube turning vernier scale vertical circle zero

### Popular passages

Page 98 - 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 center of this field of view.

Page 35 - But if the measure be taken from any point in one line, to its corresponding point on the line of the same denomination, on the other leg, it is called a transverse or parallel distance. The divisions of each sectoral line are...

Page 101 - ... 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...

Page 75 - When you have proved that the three angles of every triangle are equal to two right angles...

Page 131 - Then press downwards the branches ee, which will cause the points to make punctures in the paper at opposite sides of the circle ; which being afterwards connected, the line will pass through the given angular point, if the instrument was first correctly set. In this manner, at one setting of the instrument, a great number of angles may be laid off from the same point. It is not essential that the centre be over the given point, when applied to...

Page x - DRAWING COMPASSES. • THIS instrument consists of two legs movable about a joint, so that the points at the extremities of the legs may be set at any required distance from one another; it is used to transfer and measure distances, and to describe arcs and circles. The...

Page 94 - A second arrow being now put down by the leader, the first is taken up by the follower, and the same operation is repeated till the leader has expended 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 follower's hand shows the number of chains measured since the...

Page 54 - B, in the third square below gh, on the top line ; and a line drawn from A, in the copy, through these several points to B, will be a correct reduced copy of the original line. Proceed in like manner with every other line on the plan, and its various details, and you will have the plot or drawing, laid down to a small scale, yet bearing all the proportions in itself exactly as the original. It may appear almost superfluous to remark, that the process of enlarging drawings by means...

Page 50 - Each ruler has scales of equal parts, decimally divided, placed upon its edges, which are made sloping, so that the extremities of the strokes marking the divisions lie close to the paper. The primary divisions represent chains, and the subdivisions, consequently, ten links each, as there are 100 links on the surveying chain. Plotting scales may be procured -in sets, each with a different number of chains to the inch. The advantages of this arrangement are, that the distances required can be transferred...

Page 148 - ... 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 middle vertical wire ; and if not, loosen the screws which hold the eye-end of the telescope in its place, and turn the end round very carefully till the error is moved.