OPTICAL TELEGRAPHY, 
*9 
Nothing can be simpler than the working of this apparatus. 
It is necessary only to turn round the axle of the moveable 
mirror as often as the flashes are to be produced. M. Leseurre 
also contrived a screen made of moveable pieces like a Venetian 
blind (Fig. 5a). When the laths of the blind are open the 
beam passes, when they are closed the light is shut out. A 
handle, a , was provided for working the laths. 
The amount of light reflected does not change during the 
day, since the inclination of the revolving mirror to the 
reflected ray remains constant. But as the sun’s declination 
Fig, 5 a , 
varies from day to day, M. Leseurre placed in front of the 
revolving mirror a telescope with its optical axis parallel to that 
of the mirror. By observing the reflected rays through this 
telescope the operator was enabled to perfectly adjust his 
apparatus. 
M. Leseurre’s apparatus did not come into working operation 
in Algeria, but it was tried with the most satisfactory results 
at the Observatory of Paris, in presence of the Minister of War 
and the Director General of Telegraphs. 
The apparatus could be used with the Chappe code by means 
of conventional signals, as well as for the long and short 
emissions of light that constitute the Morse alphabet. 
Mr. Henry C. Mance, the electrician of the Persian Gulf sub¬ 
marine telegraph, by adopting the idea of Leseurre, succeeded in 
