388 8S. Newcomb—Remarks on the late Transit of Venus. 
The induction currents resulting even from the employ- 
ment of straight soft iron armatures which had been care- 
fully deprived of residual magnetism are thus seen to be more 
than four times as strong as those obtained by merely slipping 
the induction coil on and off the limits of the electro-magnet ; 
which is, practically, the method adopted in many later forms 
of the magneto-electric engine, particularly in that of the 
Gramm machine, in which different portions of a ring-shaped 
electro-magnet revolve toward and away from the poles of a 
horseshoe magnet. When electro-magnetic armatures are used 
the effects far surpass those obtained by non-magnetic soft iron 
straight armatures, as the preceding results show. 
Professor Trowbridge suggests a magneto-electric engine of 
the following construction. The horseshoe armature is made 
to revolve about the line XX as anaxis. By the preceding ex- 
2. periments it has been 
found that when a 
north and a south pole 
3 2 I Ehs x » \ are opposed the indue- 
. X through B and A’ are 
B B’ in the same direction 
~Ls and those through B 
oe nd A are also in 
one direction. By a suitable commutator the currents circu- 
lating through the coils on the stationary magnet can be sent 
through those on the armature, and vice versa. The residual 
magnetism in soft iron is sufficient to start the induced currents. 
Instead of one stationary electro-magnet it would oye ae 
better to employ a number arranged about the axis XX. With 
projecting pieces of soft iron arranged upon the poles of the 
stationary magnets, the size of the horseshoe armature could 
be regulated to suit the varying conditions of speed. 
Experiments are now being made on this form of engine. 
Art. XLIL—Remarks on the Observations of the late Transit of 
Venus ; by Simon NEWCOMB. 
Reports more or less detailed having been received from all 
can, however, at present, only be preva on the 
h 
