512 



NEGRETTI AND ZAMBRA, HOLBORN VIADUCT, E.G., 



NEGRETTI & ZAMBRA'S IMPROVED PORTABLE HELIOGRAPH, (fig. 3135). 



Instructions for use. 

 In setting up this instrument 

 the legs must be first set up, then 

 the long arm (which carries sighting 

 vane) put on and lightly clamped. 

 The instrument can then be firmly 

 screwed on the tripod. The centre 

 is fitted tightly in socket of staff - 

 head, which is of simple construction, 

 especially designed for this Helio- 

 graph, with the milled head for 

 horizontal motion on the left hand 

 when mirror is facing distant station 

 the length of flash can be regulated 

 by means of capstan screw on saddle 

 piece over the lever arm. As all 

 the important screws are capstan 

 heads they can be tightened by the 

 capstan pin. 



TO USE THE HELIOGRAPH. 



Sighting with Sun in front of 

 Signaller. 



The usual method of directing 

 the flash to the required point has 

 been to look through the mirror 



FIG. 3135. from the back and move the sighting 



vane until the sighting point is exactly in line, but a simpler and very accurate 

 way is to stand in front of but a little on one side of mirror, and looking into it 

 bring the mirror, by means of horizontal and vertical screws, into such a position 

 that the spot in centre of mirror cuts off the reflection of distant station; then 

 move the sighting rod until the reflected image of sighting vane come into an 

 exact line with the sighting vane and distant station. The flash is then thrown on 

 to the vane (which must be firmly clamped and not shifted), and is rightly aligned 

 when the dark shadow spot from centre of mirror is thrown on vane. The mirror 

 must be moved up and down to the right or left until the spot falls on the vane 

 it is then ready for use. 



Sighting with Sun behind the Signaller. 



When it is necessary to use both mirrors, place the signalling mirror facing 

 the sun and the auxiliary mirror inclining to the distant station, stand in front of 

 the Heliograph and looking into the mirror, so that the whole of the auxiliary 

 mirror can be seen reflected. Move the latter horizontally or vertically until the 

 distant station, the spot on the auxiliary mirror, and the unsilvered spot on the 

 signalling mirror are in the same line ; the auxiliary mirror can then be firmly 

 fixed in its socket, and the mirror clamped with the nut at the side. 



In signalling the left hand is kept on the milled head and the right on the 

 signalling key, the necessary adjustments to suit the motion of the earth, and 

 keep the shadow spot on the sighting vane, can thus be made while in the act of 

 .signalling without interruption or delay. For prices, see page 348. (No. 1735.) 



