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telegraph lines, for increasing the rate of signaling, and in many ways 
increasing the expedition with which messages can be sent. Of course 
the success of many of these contrivances and even their invention de- 
pended on increased knowledge of the laws of electricity and magnetism. 
For example, effective duplexing, quadruplexing, etc., depends on a proper 
understanding of the effect of the electrostatic capacity of the line, and 
this was not understood properly until the mathematical investigations of 
Thomson and others cleared the matter up. For the impetus toward dis- 
covery in this direction, again, we are largely indebted to telegraphy, for 
much of that class of work was suggested by the difficulties encountered 
in signaling through long submarine cables. 
The invention of the telephone is fast becoming ancient history, yet it 
will always mark one of the greatest of the useful applications of elec- 
tricity. It does not call for more than a passing remark here, because 
electro-magnetically it is all in Faraday and Henry’s papers. The radio- 
phone should be mentioned because it marks the application of the dis- 
covery by May and Smith of the effect of light on the resistance of 
selenium. This effect has since been found in the case of a large number 
of other substanees, but it is still an interesting field for research. A 
number of experiments on this subject have been associated with attempts 
to make things visible at a distance. No doubt it will ultimately be pos- 
sible not only to talk to a distant party, but also to see the party talked 
to, and thus, as it were, look the party in the eye with whom you are 
conversing. 
The subject of telegraphy is closely associated with the present excel- 
lent system of electrical measurements and with the invention of many of 
our most delicate measuring instruments. As the applications of electricity 
increased there gradually grew up a new branch of engineering, a branch, 
however, in which the foot rule, pound weight, chronometer and ther- 
mometer were not sufficient. Other standards of measurement were re- 
quired in order that quantities could be gauged and consistent work done. 
The way to connect the measurement of the new quantities with the units 
already in use in dynamics had been pointed out by Gauss and others, 
and at the suggestion of Thomson the British Association appointed a 
committee in 1861 to determine the best standard of electrical resistance. 
This led to an unexpected amount of work, not only on a standard of re- 
sistance, but also on the general subject of electrical measurements. The 
committee regretted at the end of the first year that it could not give a 
