88 Intelligence and Miscellaneous Articles. 



Through the kindness of Mr. Eutherford I have recently come 

 into possession of one of them, having a ruled surface of something 

 more than a square inch, the lines being spaced at intervals of ^ 4 * g 

 of an inch. Combining this with the collimator and telescope of a 

 common chemical spectroscope, we get an instrument furnishing a 

 spectrum of the first order, in which the D lines are about twice as 

 widely separated as by the flint-glass prism of 60° belonging to the 

 original instrument. In the neighbourhood of C the dispersion is 

 nearly the same as would be- given by four prisms. 



The spectra of the higher orders are generally not so well seen, 

 on account of their overlapping each other ; but fortunately with 

 one particular adjustment of the angle between the collimator and 

 telescope, the C line in the spectrum of the third order can be 

 made to fall -in the vacant space between the spectra of the second 

 and fourth orders, and we thus obtain an available dispersion nearly 

 the same as that of the instrument I am accustomed to use. 



On applying the new instrument to the equatorial, I found (under 

 atmospheric conditions by no means favourable, though the best 

 that have presented themselves as yet) that in the first-order spec- 

 trum I could easily see the bright chromosphere-lines C, D 3 , and E ; 

 I could also, though with great difficulty, make out Hy,(2796K). 

 On opening the slit the outline of the chromosphere and the forms 

 of the prominences were well seen in the spectra of both the first 

 and third orders, quite as well, I think, as with my ordinary instru- 

 ment in the same state of the air. The spectra are, of course, 

 fainter ; but as this loss of light affects the background upon which 

 the prominences are projected as well as the objects themselves, it 

 does not materially injure their appearance. 



The grating is much lighter and easier to manage than a train of 

 prisms ; and if similar ruled plates can be furnished by the opticians 

 at reasonable prices and of satisfactory quality, it would seem that 

 for observations upon the chromosphere and prominences they 

 might well supersede prisms. — Silliman's American Journal, June 

 1873. 



DUPLEX TELEGRAPHY. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 It may be 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. 



Yours obediently, 



H. HlGHTON. 



Putnev, June 11, 1873. 



