24 



The upper halves of the four sides also should have 'CARE' un<1 'KEEP 



DRY' marked in lawe letters on them. These precautions ar> //"//*/><//*,//,/, iw 

 safe conveyance \vhile in the hands of inexperienced persons, as \\iiln.nt tin-in mes- 

 sengers will often cany them wrong side up. 



The tripod needs packing simply in a close-fitting box. If not placed in a box, 

 it often happens that legs or shoes are broken off while en route, or that the tripod 

 bead becomes bent. 



Many hundreds of instruments, packed as explained above, have been shipped 

 l>y us. travelling over thousands of miles, over rough roads, on stagesandon horse- 

 back; and the instances are so rare where one has become injured (and then only 

 through gross carelessness), that this mode of packing must be regarded as the 

 <>nly proper one for conveying instruments of precision by express or other public 

 carriers. 



Arriving at its destination, an instrument should not remain packed up with 

 cushions, etc., any longer than absolutely necessary. Tin- atmosphere in such 

 boxes naturally must be close and often moist, and consequently lias a tendency to 

 produce the ill effects by moisture mentioned in preceding paragraphs. 



Some Remarks Concerning Instrument Adjustments. 



The mechanical and optical condition of instruments used in geodesy, and their 

 adjustments, although satisfactory when they leave the maker's hand, are liable to be- 

 come disturbed by use. It is therefore of vital importance that the person using an in- 

 strument should be perfectly familiar with its manipulations and adjustments. He 

 should be able to test and correct the adjustments himself at any time, in order to save 

 trouble and expense, as well as to possess a thorough knowledge of the condition of the 

 instrument. It is evident that if the character of an instrument is not properly under- 

 stood or if the adjustments are considerably out, the benefit due to superior design and 

 workmanship may be entirely lost. Under these circumstances an instrument may 

 be little better than one of lower grade. 



In the best types of modern instruments the principal parts are so arranged that 

 they can be adjusted by the method of reversion. This method exhibits an existing 

 error to double its actual amount, and renders its correction easy by taking one-half 

 the apparent error. Thus errors of eccentricity and inaccuracy in the graduations are 

 readily eliminated by reading opposite verniers and reversing the vernier plate 180 on 

 the vertical center and taking the mean of the readings , and by repeating the measure- 

 ment of an angle by changing the position of the limb so that the measurement will 

 come on different parts of the graduation. The striding levels and levels mounted on 

 a metal base are readily tested by reversing their position"! end for end. In the 

 transit plate-levels the adjustment is assured by turning the vernier plate 180. Errors 

 of the line of collimation are detected or eliminated by reversing the telescope over 

 the bearings, or through the standards, as the case may be. In short, an instrument, 

 the important parts of which are not capable of reversing in one way or another, cannot 

 be examined quickly and accurately. 



The adjustments of an instrument, and particularly those of its cross-wires, should 

 be taken up successively in a systematic manner. The proper way is to select a place 

 from which they can be conducted in succession without moving the instrument, as 

 none of the adjustments should be completed independently of the others. This method 

 is followed by the maker, and will save time and vexation. Any auxiliary apparatus 

 that may be available, such as collimators, etc., will be of great service and expedite 

 the work. One of the most important considerations in making adjustments (when 

 the same are greatly disturbed, as when new wires are to be inserted), is to place all 

 the respective parts in an approximate adjustment without introducing any strain 

 except what properly belongs to the action of the adjusting screws themselves. The 

 more natural the method, and the less internal strain introduced in bringing these ad- 

 justable parts into position, the more lasting will be the final adjustments, provided the 

 instrument is otherwise in good condition. 



It is important that all adjusting screws and nuts should fit truly on the surfaces 

 against which they operate, with only a mere film of tallow between them, so as 

 to insure a true metallic contact, and that they be brought to a firm bearing, yet with 

 out excessive strain. Opposing screws and nuts should always work somewhat freely, 

 so that one can feel when they come to a true bearing. A moderate pressure 



