T' ,,,.|- the D lines are about twice as 



""'L prism of 60° belonging to the 



I ,,) rhoo d of C the dispersion is 



lln by fo" 1 P risms - 



iders we generally not so well seen, 



" each other; but fortunately with 



angle between the collimator and 



neb-urn of the third order can be 



■^between the spectra of the second 



available dispersion nearly 



accustomed to use. 



equatorial, I found (under 



favourable, though the best. 



that iu the first-order spec- 



phere-lines C, D 3 , and F- 



, make out Hy, (2796 K). 



mosphere and the forms 



spectra of both the first 



pith my ordinary instru- 



ipecrra are, of course, 



tli.- liackground upon which 



. projected as well as the objects themselves, it 



injure their appearance. 



SS££WJU*nr cuaht, it would 1 seem that 

 for observations upon the chromosphere and prominences they 

 mYght well supers* prisms.-Silliman's Amencan Journal, dime 

 1873. 



DUPLEX TELEGRAPHY. 



To the Editors of the Philosophical Magazine and Journal. 

 GsjraiEMM, 

 It, may he as well to say that the plan of duplex telegraphy by 

 means of two batteries, working together on the receiving instru- 

 ment, but counteracting one another on the instrument at the send- 

 ing end, was patented by me some months since. It is one of the 

 many instances in which a plan occurs to two different people 

 nearly at the same time. 



Tours obediently, 



H". Htghto.w 

 Putney, June 11. 1873. 



