108 



lar to the above, and differs only in so far as the now lmri/<mt;il wire of the auxili- 

 ary telescope must bo mude to bisect a point previously bisected by tin- horizontal 

 wire of the main telescope. This is done by slightly turning the vernier plate on 

 it - \ !( ical axis and by making use of the same milled-headed tangent scn-ws. 



Thus it will be seen that the ready InterohfUlgeability of 1 he au.\iliai-\ telescope 

 enables one to read horizontal as well as vertieal angles when the main telescope 

 a n not be used, obviating the making of corrections for the excentricity of the tele- 

 scope in both positions. 



Style I, with non-adjustable central port (see paff<> 17 . 



The general design of this arrangement of attaching the Interchangeable tele- 

 scope and the method of manipulating it are, quite similar to that described under 

 style 11. It differs from the latter only in so far as it is not provided with an ad- 

 justable trivet. In this device Style I, the auxiliary telescope screws direct upon 

 an open central vertical post cast in one piece with the transverse axis to secure 

 great rigidity, the degree of accuracy of the result depending in a large measure 

 upon the degree of accuracy with which the center of the pillar, and the line of 

 collimation of the principal (then vertical) wire of the fiuxiliary telescope an- 

 made to lie in the same vertical plane as the optical axis of the main telescope or 

 parallel to it. With the care given to it and special machinery used for it, this 

 condition, difficult as it is, is secured to an extent which leaves little to be desired 

 for all practical purposes. As the auxiliary telescope is interchangeable from top 

 to side there is really need of but one wire, which we will designate as the princi- 

 pal wire. This, when the auxiliary is mounted on top, is the vertical wire, and 

 when on the side becomes the horizontal wire. Therefore it will be seen that. 

 whtMi the auxiliary is mounted on top the line of collimation of its horizontal wire 

 is immaterial, as no vertical angles will then be measured. When the latter are to 

 be measured the engineer will then mount the auxiliary on the side, when in turn 

 the vertical wire becomes immaterial. The auxiliary telescope is provided with 

 two milled-headed opposing screws (same as in style II), for ranging in line with 

 the main telescope. 



Style I being more rigid, simpler and cheaper than style II, is now recom- 

 mended. In neither of the two styles does the auxiliary telescope ordinarily 

 revolve in a socket for the purpose of making the adjustment of collimation, and 

 coincidence of the cross- wires and optical axis must be verified by the use of impro- 

 vised wooden wyes (see above) should it become necessary. 



The success which the interchangeable auxiliary telescope has achieved, both 

 here and abroad, since first invented by this firm in 1895 is somewhat phenomenal. 

 It shows that this combination is the most applicable one in solving the difficult 

 problems arising in mine engineering. For this reason every preparation has 

 been made to meet the demand and new improvements are added as experience 

 may suggest. All our top telescopes are therefore now made interchangeable. 



Credit is due, in working out the feasibility of using the top and side telescope 

 interchangeably, to Mr. Dunbar D. Scott, mining engineer, for several valuable 

 suggestions gathered from his experience and needs in mine work. 



The Use of the Interchangeable Auxiliary Telescope 

 for Astronomical Observations. 



Besides its ordinary use for steep sighting in mines, the interchangeable auxiliary 

 telescope, as described in the foregoing article, will at times be found very useful as 

 an astronomical instrument. It is particularly advisable in making latitude observa- 

 tions by meridian altitude and in observing transits across the meridian for time. As 

 a rule when the prism is attached to the eye-piece of the main telescope it is not pos- 

 sible with the engineer's mining transit to point the telescope at a greater angle of 

 elevation than about 70, consequently it would be impossible to make solar observa- 

 tions at a latitude lower than 40" when the sun is at its greatest declination or obser- 

 vation On Stars near the Zenith. However, by attaching the prism to the auxiliary telescope 



uttdM*topor0ideteleaeope,the8C obseirattonamajbemadewitheaseandthladifficulty overcome, 



In making latitude observations the interchangeable auxiliary telescope should be 

 attached at, the side; and its horizontal wire is then, by means of the two oppos- 

 ing tangent si-rews. made to correspond to the line of collinmtion of that of the main 

 telescope by bisecting with both telescopes some distaufand well-defined object : then. 

 if a meridian mark is used which is not, absolutely necessary), the transit should be 

 setup in the meridian by the main telescope and the pointing on the sun or star may in- 

 made with the auxiliary telescope with or without the prism, as conditions may re. pure. 

 ! the auxiliary ti-le.-c.,jM- should be mounted on top and rau-ed 

 into line with the vertical wire of the main telescope by using the two opp 

 screws as explained. 



In iiKikiuir -.lar :m<l stHhir observations with the main telescope and pri-ni atta< -him-nt, thr trle- 

 scope should always be reversed through the standards with the objective down in-tcad o| up 



