180 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. . 
sufficiently high frequency oscillations by the are method unless at 
least 1 or 14 horsepower is being expended in the are. Hence, for 
short distance work on the point of economical working as well as 
simplicity of apparatus and ease of working the spark method has 
advantages denied to the arc. We were told not long ago by an 
eminent electrician that the are method of creating undamped waves 
sounded the death knell of spark telegraphy. «It is always advisable 
to exercise some caution in issuing obituary notices of well tried in- 
ventions prior to their actual decease, and in this case although the 
power to create continuous trains of electric waves will doubtless 
greatly assist space telegraphy, it does not follow that their gener- 
ation by the arc method is the best or final method. 
In the production of continuous oscillations we are not limited to 
the are method. Mr. Marconi has for some time past been engaged 
in developing an ingenious method of creating undamped electric 
waves for telegraphic purposes which involves neither an are nor 
alternator, but is a new mechanical method of great simplicity. 
This method is capable of pro- 
ducing astonishingly large alter- 
nating currents of very high fre- 
quency, in other words, so called 
undamped or persistent oscilla- 
tions. I have recently witnessed 
some of his experiments, and was 
surprised at the results obtained. 
Long distances have been tele- 
graphically covered with every 
prospect of great efficiency. Un- 
fortunately, the incomplete state 
of certain foreign patents prevents 
me from entering into details of 
this method now, but I hope he 
himself will be able to do so soon. 
Turning then from transmitters to receivers, we may notice one or two 
recent types. By far the larger portion of electric wave telegraphy 
was until a few years ago conducted by means of some form of coherer, 
either requiring tapping or else self-restoring. The coherer in certain 
forms has the advantage that a current of about 0.1 to 1.0 milliampere 
can be passed through it, and hence through a relay, so that messages 
can be printed down by it when using a Morse inker in dot and dash 
signals. After that came Mr. Marconi’s magnetic detector, making use 
of a telephone to create an audible signal. This is now the instrument 
employed by him on all long distance work. In Germany and the 
United States a type of telegraphic wave detector has come into use, 
commonly called the electrolytic receiver. In one form it was invented 
, 
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Hie. 12: 
Hlectrolytie detector. 
