ON SOME MARVELS IN TELEGRAPHY. 233 



marvel of mere telegraphic communication, somewhat the 

 same relation which the marvels of spectroscopic analysis as 

 applied to the celestial orbs bear to that older marvel, the 

 telescopic scrutiny of those bodies. In each case, also, 

 there lies at the back of all these marvels a greater marvel 

 yet electricity in the one case, light in the other. 



I propose in this essay to sketch the principles on which 

 some of the more recent wonders of telegraphic communica- 

 tion depend. I do not intend to describe at any length the 

 actual details or construction of the various instruments 

 employed. Precisely as the principles of spectroscopic 

 analysis can be made clear to the general reader without the 

 examination of the peculiarities of spectroscopic instruments, 

 so can the methods and principles of telegraphic communi- 

 cation be understood without examining instrumental de- 

 tails. In fact, it may be questioned whether general 

 explanations are not in such cases more useful than more 

 detailed ones, seeing that these must of necessity be in- 

 sufficient for a student who requires to know the subject 

 practically in all its details, while they deter the general 

 reader by technicalities in which he cannot be expected to 

 take any interest If it be asked, whether I myself, who 

 undertake to explain the principles of certain methods of 

 telegraphic communication, have examined practically the 

 actual instrumental working of these methods, I answei 

 frankly that I have not done so. As some sort of proof, 

 however, that without such practical familiarity with working 

 details the principles of the construction of instruments may 

 be thoroughly understood, I may remind the reader (see p. 96) 

 that the first spectroscopic battery I ever looked through 

 one in which the dispersive power before obtained in such 

 instruments had been practically doubled was of my own 

 invention, constructed (with a slight mechanical modification) 

 by Mr. Browning, and applied at once successfully to the 

 study of the sun-by Mr. Huggins, in whose observatory I saw 

 through this instrument the solar spectrum extended to a 

 length which, could it all have been seen at once, would have 



