14 



whatever. As a rule more harm than good comes to the instrument. It is only in 

 case of emergency that such heroic treatment should be resorted to. When cleaning 

 the slide and inside of main tube great care must be taken not to break the wires. 



To focus the wires sharply turn die eye-piece slightly to the right or left 

 as the case may be. Remove parallax as explained on page 48. 



To clean the threads of leveling or tangent screws when working hard, use a st it) 

 tooth brush to first clean the threads of all dust, then apply a Little oil, and work 

 the screw in and out with alternate brushing to remove dirt and all oil until it 

 moves perfectly free and smooth. 



Screws for the adjustment of cross-hairs should not be strained any more than 

 ~;uy to insure a firm seat; all straining of such screws beyond this simply 

 impairs the accuracy of instrument and reliability of adjustment. 



When in the lield always carry a Gossamer water-proof for the instrument in 

 you* poeket, to put over it in case of a shower or dust cloud. On reaching oiliee, 

 after use of instrument, dust it off generally with another line brush ; examine the 

 centers and all other principal movements to see if they run perfectly free and 

 and oil them if necessary; also examine the adjustments. This will save 

 expense and many hours of vexation in the field. 



Care of Centers and Graduation. 



As the centers, the telescope axis and the graduations require greater care to 

 rve their line qualities, perhaps it is not amiss to say a few words concerning 

 their treatment. 



I pon finding that the centers do not revolve as free as usual after exposure of 

 the instrument in an extremely hot or cold weather, they should be cleaned as soon 

 as time permits, and then proceed as follows : 



Unscrew the milled-head nut at the extreme end of the cylindrical tube containing 

 a spiral spring, which is opposite the upper tangent screw. Do it somewhat cau- 

 tiously, or the spring will fly out. Then unscrew a small cylindrical case, which 

 also has a milled edge, and which is at the bottom of the centers. This case contains 

 a small triangular spring to balance the upper weight of the instrument within a 

 tew 11 is. Be careful to keep the face of this spring up in its case, which is best 

 indicated by a bright point in its center. After unscrewing the nut attached to the 

 inner center, a gentle pressure upwards will lift the vernier plate out from the lower 

 part of the instrument. Take a fine camel hair brush, and with it clean the gradua- 

 tion, the verniers and the inner part of the instrument, but do not rub the graduation, 

 especially not its edge, then take a stick of about the same taper as the inner center, 

 wrap some wash-leather slightly soaked in line oil around it, and clean the. insides 

 of the sockets as carefully as possible; then remove this piece of wash-leather and 

 wrap a fresh piece without oil around the stick and clean dry. Proceed similar with 

 the centers and their flanges. 



Before applying fresh and pure watch oil, however, care should !> taken that 

 not a particle of dust or other foreign matter is loll in the sockets, on the centers, 

 or on the graduation. This caution having been taken, the fresh oil should be well 

 di.-tributeu on all the bearing parts. It will be well to also examine the arm of t lie 

 clamp screw of the circle and telescope axis, and if necessary clean by removing 

 \\a-ber. After the instrument ; .s thoroughly cleaned and oiled, the mils and springs 

 s-re\\ed back to a firm seat, the instrument must turn perfectly iVee and yield at 

 the slightest touch of the hand. 



To remove dirt and oxyd that may havo accumulated on tho .surface of a solid 

 graduation, apply some fine watch-oil, and allow it to remain for a few hours; 

 take a soft piece of old linen and slightly rub until drv, but without touching tbe ed-:o 

 of the graduations. If, after cleaning, the solid silver surface should show alter- 

 nately bright er spots which would interfere somewhat with the accurate reading of 

 the graduation, barely moisten the finger with vaseline and apply the same to tlu> 

 surface; then \\ipr the finger dry and lightly rub it once or twice around tho 

 graduation. Avoid touching the edges as much as possible. Sin -h cleaning, ho\\- 

 must only be resorted to when absolutely necessary, and then only with the mvatest 

 care, as it is too apt i> reduce the minuteness of the graduation, ami spoil its iim 

 appearance. If, after such cleaning, dirt and grease ha- accumulated on the inner 

 edge of the graduation and verniers, gently wipe clean before restoring the vernier- 

 plate to its place. Kemember, also, that the centering of the graduations of tho 

 circle and verniers Is a most delicate adjustment to make. The-e should never bo 

 unscrewed from their flanges by anybody except a maker. 



