Correspondence. 109 
rapidity is measured by a register or counter on which it acts; an endless 
serew fixed upon the axis of the windmill works into a system of cog- 
wheels, so combined, that when the last makes one turn, the windmiil 
makes 500. The apparatus being fixed on the axis of the vane and per- 
being isolated from the apparatus by plates of ivory. If then, at the 
i e 
windmill. The current in connection with a part of the apparatus 
will then be closed at intervals more or less distant. 
The current is transmitted to the windmill “a means of the axis of the 
8 ; soe 
mediate plate of i loorys this ring may be put into communication with 
the spring of the counter ; and the current may be closed or interrupted 
e 
servers apartment the various changes, M. Dumoncel introduces into 
the circuit formed by each of the eight wires corresponding to the dif- 
ferent winds, an electro-magnet whose armature is furnished with a 
crayon which falls whenever the current is established, and leaves i its 
1 
crayons of the vertical electro-magnets come in contact with it est : 
point whose height on the cylinder indicates the direction of the w 
