107 



telescope to be verified as explained in "To make the vertical wire perpendicu- 

 lar to the plane of the horizontal axis," etc., p. 48. 



To place the line of collimation of the auxiliary telescope in the same vertical plane 

 with that of the main telescope. Bisect a distant 'object with the vertical wire of the 

 main telescope ; see if the vertical wire of the auxiliary telescope also bisects the same 

 point. If not, move the auxiliary telescope by means of the pair of opposing milled- 

 headed screws attached to its pillar nearer the eye-end until the distant object is 

 bisected at the same time by both vertical wires. Now focus the main telescope on a 

 near object and see if the vertical wire of the auxiliary telescope bisects the same 

 point as the vertical wire of the main telescope. If not, make the adjustment by 

 means of the pair of capstan-headed opposing screws on one side of the adjusting 

 trivets of the pillar. Then re-examine both wires for coincidence with the distant 

 object, using the milled-headed screws, and also repeat the adjustment for near object 

 if necessary. The two lines of collimation are now in the same vertical plane. 



To adjust the top telescope so that both horizontal wires bisect the same distant 

 object. Bisect a distant object with the horizontal wire of the main telescope, and see 

 whether the horizontal wire of the auxiliary telescope bisects the same point. If not, 

 make the coincidence by means of the pair of opposing capstan screws in the trivets 

 near the milled-headed screws. This being done, both these adjustments should be 

 verified and repeated if necessary. These adjustments once carefully made assure 

 the exact parallelism of both telescopes and will not require repetition except at long 

 intervals, or after an injury. 



The distance between the lines of sight of the two telescopes should be carefully 

 measured by sighting at a vertical line on a wall the telescopes being horizontal 

 when the distance between the intersections of the two horizontal wires on the line will 

 be the eccentricity of the top telescope, for which every vertical angle measured with 

 it should be corrected. 



The adjustment of the extra level (if any is provided in place of a striding level, 

 see footnote, page 158) near the eye-end of the telescope, as shown in the cut p. 165, 

 is dependent on that of the telescope in the vertical plane. This latter must be verified, 

 as explained on page 51, before this level can be adjusted by reversing, as in case of 

 the plate levels. 



Patent Adjustable and Interchangeable Auxiliary 



Telescope. 



Style II with adjustable trivet, page 165. 



In this device the auxiliary telescope is the same as described under " Patent 

 Adjustable. Top Telescope" (see cut, page 167), but it is so arranged that it can be 

 attached (interchangeably) on top or at the side of the cross-axis of the transit and 

 readily ranged into line with the main telescope. The excentricity will be the 

 same in both cases. One counterpoise will be sufficient for both positions. 



This improvement used as a side telescope cannot, however, be carried out 

 with all instruments, since the cross-axis requires an extension ending in a 

 threaded stud beyond the standards, and this to be enduring can be made only on 

 the original instrument and cannot be attached to an old axis. From this it will 

 be seen that this is only applicable to new instruments when so ordered. 



The auxiliary telescope detaches from a stem permanently fixed to the cross- 

 axis so that the excentricity is the same when it is placed on the side. It does not 

 revolve on an independent hub, as before, with which style there was always 

 danger of accidentally changing its position, but this device is simply ranged into 

 line with the main telescope by use of the milled-head screws. However, to meet 

 every want arising in a mine, it is provided with a clamp ring and capstan-headed 

 screw, by which the auxiliary telescope may be changed on its hub and per- 

 manently secured in any position. When used as a side telescope the fine adjust- 

 ment by the trivets is not so essential as is the case when used as a top telescope, 

 where the accuracy cannot be too great and where the trivets are therefore essen- 

 tial, since the top telescope is then really the main telescope for measuring hori- 

 zontal angles. To use it in measuring horizontal angles it is only necessary to bi- 

 sect with the vertical wire of the main telescope as distant a point as can be found 

 in a mine, then by means of the milled-headed opposing tangent screws, and by 

 slightly revolving the transverse axis of the main telescope, the vertical wire of 

 the auxiliary one must also be made to bisect the same point. 



To use it as a side teleseope for vertical angles the procedure is exactly simi- 



