124 
WIRELESS TELEGRAPHY* 
have been to discover more precisely tlie conditions necessary to assure 
success rather than to work through any record distances. This is the 
apparatus actually used at Dover (apparatus shewn). I am indebted 
to Mr. Gavey, of the G.P.O. telegraphs, who lent it me for the pur¬ 
pose of this lecture. It was Mr. Gavey who conducted the Post Office 
experiments at Dover and elsewhere. 
(Experiment shewn:—The great sensitiveness of the Dover set was 
shewn by the fact that it could be set in action from the minute oscil¬ 
lations produced by an ordinary trembling bell.) 
It is not very well known to most people, perhaps, that when they 
ring an ordinary electric bell in a house they are setting Hertzian 
waves in motion. That is, however, a fact; and advantage is taken of 
it to test the sensitiveness of a Marconi receiving set. I have here 
(shewn) a small electric bell and a single cell. You will see that the 
very feeble electro-magnetic waves sent out when the bell is rung will 
work this sensitive apparatus at a distance of two or three yards 
(applause). 
It has been stated that “ weather seems to have no influence, and 
that rain, fog, snow and wind avail nothing,” but in the light of more 
recent experiments it would appear that some slight influence is 
exerted by rain and mist affecting the distance over which transmis¬ 
sion is possible ; and further that signals may be sent a greater dis¬ 
tance across water than across land. Perhaps it would be desirable to 
add that these last statements are personal impressions formed from 
experimental results up to date. 
I have entered into some detail regarding the apparatus for sig¬ 
nalling in both Preece's and Marconi's system, because the nature of the 
apparatus determines to a great extent the uses to which it can be put. 
As to which of these systems is most capable of general application 
I have little hesitation in expressing my own opinion, that Marconi's 
shows greater possibilities than the other. The conditions are more 
elastic. It is not always feasible to run two parallel circuits of con¬ 
siderable length, and as for experimenting with Preece's system it is 
practical^ impossible for private individuals who have not a large es¬ 
tate at their proposal or the facilities of the post office authorities. I 
may tell you that I have not made any experiments over long distances 
with Preece's for the reasons I have just given. I have, however, 
made experiments over a considerable distance with the other system. 
The vertical wire has been condemned as the greatest disadvantage 
of Marconi's system, but to raise a vertical wire is a more feasable and 
rapid operation than running a long line of elevated insulated wire. 
In a wind a kite will raise the wire, and in a calm a small balloon 
might be used. Tall trees, steeples, flag staffs, towers, or cliffs can be 
taken advantage of as occasion offers. It appears to me that one of 
the drawbacks of Marconi's apparatus is the necessity of providing a 
powerful and efficient battery for working the induction coil. That 
would perhaps limit its use in the field where one knows what a trouble 
it is to make up really good and powerful batteries. Secondary bat¬ 
teries are the best. No doubt the fact I have just mentioned would 
