USE OF THE HELIOGRAPH 169 



Section 103 Heliographs on Patrol Routes 



The use of heliographs by patrolmen or other moving units of a forest-protection 

 force brings up the question of light weight and ready portability, as previously men- 

 tioned. Such use is only practicable on a forest equipped with a permanent lookout 

 system for fire detection, and then only under topographic conditions which make it 

 readily possible for patrolmen to find points easily and quickly from which they can 

 open communication with lookout stations. This is not often practicable in a heavily 

 timbered region of little relief, but is easily accomplished in any rolling, hilly or 

 mountainous country. 



For patrol purposes, the Godwin or Forest Service heliograph is the only practical 

 type. Its weight and size make it an entirely practicable equipment for any kind of 

 patrol and its range is sufficient for most forests where it might be employed. A use 

 for this instrument will exist wherever the standards of protection employed make it 

 impossible to secure rapid enough communication by message carried to the nearest 

 telephone station. Of course, the degree of development of the telephone system will 

 exercise a very considerable influence on this time interval, but as long as it remains 

 necessary to establish a physical connection with a telephone wire in order to use the 

 line and as long as maintenance charges remain as they are, very large areas in all 

 forest regions must necessarily remain without immediate telephone service. Con- 

 ditions may vary all the way from a protection staff which depends entirely on the 

 heliograph for intercommunication between all units to a staff which uses the helio- 

 graph merely as an emergency auxiliary, placing its dependence primarily on a tele- 

 phone system. The difference will result from the protection standards employed, 

 that is the maximum of average annual damage to which the protection system is 

 designed to restrict the forest fire loss. 



CHAPTER XIX 



USE OF THE GODWIN HELIOGEAPH 

 Section 104 Parts of the Instrument 



LIST OF PARTS 



The complete instrument consists of a sole-leather case with shoulder-strap con- 

 taining: (a) One sun mirror, (b) one station mirror, (c) one screen, (d) one sighting 

 rod, (e) two mirror bars; the above in two padded wooden packing blocks; and (f) 

 one tripod with leather cup for points. 



The heliograph and case is 10 by 5J by 2 in. outside dimensions and weighs 4 

 pounds 9 ounces. The tripod folded is 2 in. in diameter by 23 in. long and weighs 7 

 pounds 3 ounces. 



(a and b) Mirrors. Two plane mirrors each 2| in. square are employed. These 

 are very carefully constructed so as to have both surfaces parallel, are backed with pure 

 silver, and varnished. Each is mounted in a black metal frame and swings in a yoke 

 on pivots at the sides. A slow-motion adjusting screw is provided by means of which 

 the mirrors when set up may be rotated on the line between these pivots as an axis. 

 This axis passes through the centre of the mirror. In the centre of each mirror there 

 is an unsilvered spot -fa in. in diameter. On the lower side of the yoke there is a 

 tapered stud which fits into a hole at the end of the mirror bar when the instrument 

 is set up. Both mirrors are exactly alike and may be used interchangeably, except 

 that when both are employed at one time it is necessary to paste a small white paper 

 disk in the centre of one of the mirrors on which to hold the " shadow spot." The 



