A Treatise on Mathematical Instruments ...

Contents

 PART 1 Triangular Compasses 7 Protracting Scales 15 Gunters Lines 27 Coggeshalls Sliding Rule 56 Management of Drawing Paper 66 Land Chain 97 Y Level 103
 Levelling Staff 109 Water Level 119 Artificial Horizon 128 Circular Protractor 136 Station Pointer 143 Troughtons Reflecting Circle 149 Method of Observing with the Transit 160 The Reading Microscope 170

Popular passages

Page 72 - ... that the sine of the angle of refraction bears a constant ratio to the sine of the angle of incidence...
Page 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 center of this field of view.
Page 78 - When you have proved that the three angles of every triangle are equal to two right angles...
Page 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...
Page 152 - The advantages of this instrument, when compared with the sextant, are chiefly these : the observations for finding the index error are rendered useless, all knowledge of that being put out of the question, by observing both forwards and backwards. By the same means the errors of the dark glasses are also corrected ; for if they increase the angle one way, they must diminish it the other way by the same quantity. This also perfectly corrects the errors of the horizon glass, and those of the index...
Page 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.
Page 138 - 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 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...
Page 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...
Page 153 - ... right, when, by a sweep of the index, the reflected image of any object will pass exactly over, or cover the image of that object seen directly. The third adjustment is, for making the line of collimation parallel to the plane of the circle. This is performed by two small screws, which also fasten the collar into which the telescope screws to the upright stem on which it is mounted: this is known to be right, when the sun and moon, having a distance of one...