OPTICAL TELEGRAPHY. 
1 7 
sometimes takes place is owing only to bad manipulation. 
Just as an operator working the Morse signals through a long 
cable should be perfectly aware of the effects of currents in 
his line, and should regulate his manipulation accordingly, so 
also ought the sender of visual signals to space them in such a 
manner as to make them distinct to the eye. In this respect 
the handle of the Mangin apparatus seems to us defective ; 
but it might easily be modified so as to present absolutely the 
same form and effects as the ordinary Morse key. 
The heliograph invented by M. Leseurre, inspector of 
telegraphs, was first utilized in Algeria. Marshal Yaillant 
exhibited this apparatus before the Academie des Sciences 
(Comptes rendus , 16 June, 1856). M. Leseurre has himself 
described his apparatus in the Annales telegraphiques for 
October, 1855. This inventor, who unfortunately died at Pau 
in 1864 at the early age of thirty-six, had for his special 
object the establishment of telegraphs in the Southern part of 
Algeria, where at that time it was scarcely possible to construct 
electric lines, or even aerial telegraphs. 
The continual sunshine which in South Algeria produces an 
exceptional condition of the soil unsuitable for ordinary tele¬ 
graphs, offers also an exceptional agent for signalling by a 
system more effective than Chappe’s aerial telegraph. Mirrors 
suitably arranged can reflect the rays of the sun in such a 
manner as to form signals, and even record them. 
The range of this signalling power is limited only by the 
rotundity of the earth and by the absorption of light in its 
passage through the lower strata of the atmosphere. 
For practical use, a simple apparatus is required with 
certain and rapid action, so that it may be worked by men of 
ordinary intelligence. 
M. Leseurre has solved this problem in a very elegant 
manner. The annexed Fig. 5 will give an idea of his 
apparatus which we shall now also describe. To make the 
apparatus available at any hour of the day, M. Leseurre, 
knowing that the sun in its diurnal movement describes a 
circle round the polar axis, placed in the polar direction an 
arm carrying a mirror with its normal forming with the arm 
an angle equal to half the angular distance of the sun from the 
pole. By turning this arm on its bearings, every time that 
