=2. Nature of Fire Necessary for Observation.=-_-A considerable volume of rapid and concentrated fire is necessary to enable the strike of bullets to be observed_, and for this purpose one or more Maxim guns, or not less than two platoons, should be employed to fire. The distance and nature of the ground will determine the volume of fire required, but the greater the difficulty of observation the greater must be the volume of fire. When trying for observation, third-class shots should not be permitted to fire. =3. Method of applying Fire for Observation=--(i) =Elevation.=--An elevation well _under_ the estimated distance should first be selected, and if the fire can be observed, the elevation should be increased by not less than 100 yards at a time until the nucleus of the bullets is seen to fall on the desired spot. (ii) =Objective.=--The point at which the fire is directed may be the actual objective, or ground in its vicinity which is more suited to observation of the strike of the bullets. (iii) =Position for Observation.=--The best position from which to observe fire is behind, and, if possible, above the firers; but in this position the bullets which fall short will be most easily seen, and may be mistaken for the nucleus of the fire. Further, all shots will appear to strike nearer to the observer than is really the case. (iv) =Hints for Observers.=--To an observer on or behind a flank of the firers, shots which pass over the mark will appear to fall towards the flank on which he is posted, and those which drop short to fall towards the opposite flank. Thus, if the majority of shots seem to an observer on the _right_ flank to fall to the _right_ of the mark, the range has been _over-estimated_, and if they seem to fall to the _left_, it has been _under-estimated_. =4. Verifying Ranges by Fire.=--When there is time and opportunity for doing so, ranges which have been taken beforehand, especially those taken in preparing a defensive position, should be verified by the results of firing a number of rounds. Section =39=.--Ranging by Auxiliary Methods and by Instruments. =1.= Training in ranging should include instruction in practical auxiliary methods such as by maps and range-finding instruments. _Exercises in ranging by means of maps, range-finders, and the eye, used in combination, should form an essential part of the fire-direction practices of the annual course of musketry._ =2. Ranging by Map-Reading.=--Ranges may be ascertained by the use of small scale maps, though large scale maps, if available, will be better for this purpose. Instruction in field-sketching and reconnaissance affords excellent opportunities for training in judging distance. For map-reading, see _Signalling_ of this series; and for field-sketching and reconnaissance, see _Drill and Field Training_ of this series.