17 







Additional Suggestions Pertaining to the Care and Pro* 

 tectioii of Instruments in Field Use. 



In field use, an instrument has to be necessarily exposed to the heat of the sun, 

 and to the action of dust and water: all of these, however, singly or combined, have 

 a tendency to affect its accuracy anu endurance. While our instruments in particular 

 have been designed to guard against injuries resulting from exposure of this kind, 

 yet glaring abuses, such as to allow it to stand for hours in the hot sun, etc., without a 

 covering or shelter of some sort, may often lead to a permanent injury to its most vital 

 parts. To preserve the finer qualities of an instrument, viz., the telescope slide, the 

 lenses, the edge, of the graduation and verniers, the centers, etc., any undue unequal 

 expansion of the different parts should be prevented. A bag thrown over the instru- 

 ment when not in use, or any shelter that can be had, is to be recommended. While 

 in use, an umbrella or screen held over it will insure greater permanency of its ad- 

 justments, and the results obtained will be more accurate and uniform than when 

 carelessly exposed. 



To protect an instrument from the effects of salt water, when used near the sea 

 coast, a fine film of watch-oil rubbed over the exposed parts will often prevent 

 the appearance of oxyd. To remove such oxyd-spots as well as possible, apply 

 some watch-oil and allow it to remain for a few hours, then rub dry with a soft piece 

 of linen. To preserve the outer appearance of an instrument, never use anything for 

 dusting except a fine camel's hair brush. To remove water and dust spots, first use 

 the camel's hair brush, and then rub off with fine watch-oil, and wipe dry ; to let the 

 oil remain would tend to accumulate dust on the instrument. 



Lubricating, etc. An instrument used in a tropical or semi-tropical country, 

 or during the warm season in a northern latitude, requires more frequent cleaning, 

 and oiling than in the more temperate climes and seasons ; but so long as an instru- 

 ment works well and the centers revolve freely, it is best not to disturb it. However, 

 if necessary, proceed as described under " Care of Centers, etc." A few additional 

 remarks we give here : Should the centers or the object-slide commence to fret, they 

 should be examined as soon as possible. Once commencing to fret, it grows worse rapidly 

 and oftentimes is then beyond repairing. Never use emery or emery-paper on them, as 

 this will cause everlasting trouble afterwards. After a thorough cleaning of the slide 

 and tube (taking care not to break the cross-wires), endeavor to smooth carefully 

 the injured parts with the back of a pen-knife, and barely apply enough tallow to 

 grease the surface of the injured part. If this does not remove the trouble, a little 

 scraping of the roughened parts on the slide, and, if accessible, on the inside of the 

 tube, may become necessary, and apply a mere trifle- of finely-powdered pumice 

 stone moistened with oil. Replace the slide and grind a little by moving it in and 

 out; clean thoroughly, and with a piece of charcoal moistened with oil smooth the parts 

 thus ground on the slide. This process of grinding is a most precarious operation, 

 and generally requires the hand of a skillful workman; it should be resorted to only 

 in case of utmost necessity. Whenever permissible, recourse should be had to a 

 maker. These remarks apply equally to the centers. 



The centers of a transit should always be lubricated with fine, watch-oil only, and 

 after a careful cleaning; never apply fresh oil before thoroughly wiping off old 

 grit and oil. Rendered marrow is a most excellent lubricant for instruments made o\ 

 brass arid the many kindred alloys of copper and tin. In the varying climes of out 

 northern latitudes this lubricant becomes rigid in cold weather, and an instrument sa 

 treated will often become unmanageable in the field. Its application, particularly 

 to the centers of a transit, is therefore restricted to the warmer zones. The use of 

 watch-oil for the finer parts of an instrument, involving freedom of motion, is 

 imperative in our latitudes. 



Many parts of an instrument, especially those whose metal compositions are 

 closely related to each other, may sometimes cause trouble if simply oiled. If they 

 begin to fret and grind, but are otherwise free from grit, etc., the judicious application 

 of a little marrow may prove very beneficial, but it should be cleaned off again as 

 much as possible. The rack and pinion motion and the telescope clamp should 

 always be greased with marrow, but the clamp, tangent and leveling screws, should 

 receive as little of it as possible in the Northern States. 



Vaseline, not having as great a tendency to rigidity under similar circumstances, 

 may prove an excellent substitute for marrow, and may often be applied to level- 

 centers, where watch-oil would not give the necessary rigidity in the use of the more 



