216 Scientific Intelligence. 
cubie centimeters H and ‘50 cub. centim. of air simultaneously 
pass soe one gee a of the _— —Roy y- Acad, mies 
1872 one machine was made for producing the light, two for plat- 
ing, nn bitin weed eying he latter poli redden 10 cms. 
of pla wire ‘3 mms. in diameter. Those now made redden 
60 ems. OF the same wire, though there is no increase in the cost 
or weight. This large increase is principally due to the employ- 
w magnets in sheets of Jamin. In 1872 and 1873 
it deposits 600 grs. per hour, but requires only 50 kgmtrs. to 
run it. It therefore occupies “put one-half the space of the old 
now constructed otis a band of thin erste ‘of part ee pa pact 
half the length of the bars of the magnet, so that four large 1 
bons are used for each machine. 
The plan of putting the electro-magnet into the main — 
gives rise sometimes to a curious change in polarity. When 
But if suddenly stopped, the current induced by the electro-mag- 
net reverses the polarity of the latter, so that if the machine 18 
again started the current passes in theo opposite direction and re- 
moves the silver it ie _— ee sey fo av oid this trouble, he 
e first machine for gendiating ae light weighed 1,000 kgs-, 
the nr of the magnets weighing 250 kgs., that of f the ring 75 
he space occupied was 80 coms. on a se and 125 cms. 
high. This was used a a long time in the tower of Westminster, 
and for two years has not given Sah troatle. es h it heated @ 
little and gave saath around the commutator. The new new form 
weighs 183 kgs. and contains only 47 kgs. of copper. Its Tength 
