82 LEVELING 



it. In a general way, magnifying power and definition are 

 opposed; that is, for the same size, a low-power telescope will 

 have better definition than a high-power telescope, provided 

 the excellence of the optical construction is the same in each 

 case. 



It is well to note here, that for telescopes of the same length, 

 the inverting telescope gives considerably higher magnifying 

 power, better definition, better light, and a much more brilliant 

 "image than the erecting telescope. A well-constructed erecting 

 telescope 18 in. long may have a magnifying power of 30 diam- 

 eters, and an inverting telescope of the same length has a 

 power of about 40 diameters. 



Care of Level. The level should not be exposed to the 

 burning rays of the sun, to rapid changes of temperature, to 

 unequal temperatures on its different parts, or to dust, and 

 should not be used in rainy weather when possible to avoid it. 

 Changes of temperature disturb the adjustments, dust is 

 injurious to the bearings and the lenses, and moisture obscures 

 the lenses and is otherwise injurious to the instrument. Where 

 it is impossible to avoid working in the rain, wipe the lenses 

 frequently and carefully with a soft linen cloth, and after 

 returning to the office or camp, wipe very carefully and thor- 

 oughly, finishing with a piece of dry chamois skin, and place 

 in a moderately warm, dry place, so that every particle of 

 moisture will be removed. When carrying a level on its tripod 

 in open country, the spindle should always be clamped slightly 

 to prevent the wearing of the centers by swinging, and the 

 instrument should be carried with the object end of the tele- 

 scope down. When working in a wooded country where under- 

 brush is dense, the level should be carried with the spindle 

 undamped, so that the telescope will turn freely on the spindle 

 and yield readily to any pressure. A blow that would inflict no 

 injury upon an undamped instrument might seriously damage 

 one while clamped rigidly. 



Leveling Rods. There are two classes of leveling rods, 

 namely, (1) rods on which the graduations are sufficiently dis- 

 tinct to be read directly by the leveler, and called self-reading 

 rods, and (2) rods on which the graduations are small and 

 which have a sliding target brought into the line of sight by 



