Reph/ to Mr. Horn. 139 



the miner will now have to do, is simply to depress the lamp 

 into the lower strata of the atmo:^phere of the mine, and it will 

 relight itself; and wlien exploring an extensive magazine of 

 fire-damp, platinum wire, on Sir H.Davy's late interesting dis- 

 coverv, will be the preferable metal. The miner will not have 

 to complain of " being long in the dark." 



This instrument is now one of the most curions and interesting 

 that can possil>'v be contemplated — an envelope, open, yet im- 

 pervious tojiame — possessing within itself when extinguished^ 

 the property of exhibiting a light nvcnmifxtcd with flume, sufii- 

 «:ient to guide the miner through the dark abvsses of the earth, 

 in an inflammable and explosive atmosphere; and the means of 

 relighting itself an passing from an inflammable medium, which 

 exceeds the explosive, into the free atmosphere. This mode of 

 applying t!ie platinum wire, vou will at once ])erceive, is more 

 important than suspending it in the top of the instrument, and 

 it will not only not intercept light, but exhibit a more brilliant 

 flame. 



I am respectfullv, sir, 



Yours most obediently, 

 London, Siirry Institution, Fel). 6, 1817. - J. MURRAY. 



P. S. — I rejoice in the near prospect I have of proving this 

 in the mine itself. J. M. 



XXXIII. Rephj to Mr. Horn. % Mr. W. Pateh, 



To Mr. Til loch. 



S»R, — In the last number of your Philosophical Magazine, Mr. 

 Andrew Horn has condescended to notice some remarks 1 made 

 upon his Theorv of Vision in a former number ; aufl with that 

 suavity of manners and in that free and easy vyay so peculiarly 

 his own, without a preamble he charges me with ignorance and 

 inconnstency ; and I think myself o!)liged to him that he con- 

 fined himself to merely making the charges without attempting 

 to prove the;n : perhaps it would have been better had he given 

 the proofs and spared the insult. 



In his answer to my remarks there is one trifling oversight;— 

 he has totally forgotten to explain the dilficulties, or to reply to 

 the objections ! 



There is also a little unfairness which I have to complain of, 

 which in Mr. Horn is perhaps not strictly honourable: in my 

 attack I made use of reason, but he has defended himself with 

 insolence. 



Mr, Horn allows that light excites sensation by acting upon 



the 



