Miscellanies. 367 



pared was fully ascertained and acknowledged. On the evening of 

 the 25th of May, when there was no moon light, and the night dark, 

 with occasional showers, the appearance of the light viewed from 

 Blackwall, a distance of ten miles, was described as being very splen- 

 did. Distinct shadows were discernible, even on a dark brick wall, 

 though no trace of such shadows could be perceived when the other 

 lights, consisting of seven reflectors with Argand lamps, and the 

 French lens, were directed on the same spot. Another striking and 

 beautiful effect peculiar to this light was discernible when the reflec- 

 tor was turned, so as to be itself invisible to the spectator. A long 

 stream of rays was seen issuing from the spot where the light was 

 known to be placed, and illuminating the horizon to a great distance. 

 As the reflector revolved, this immense luminous cone swept the hor- 

 izon, and indicated the approach of the light long before it could it- 

 self be seen from the position of the reflector. These effects, how- 

 ever, on a moon-light night, or in hazy weather, cease to appear. — 

 Ibid. 



4. Original decomposition of Potash. — Dr. Paris, in his interest- 

 ing biography of Sir Humphrey Davy, after giving an account of the 

 preliminary experiments which led to the final and most successful 

 result, has taken from the manuscript Journal of the Laboratory of 

 the Royal Institution, a fac-simile of the minute, in Davy's hand writ- 

 ing, of the successful experiment of October the 19th, 1807. It is 

 highly interesting and characteristic, but it should have been accom- 

 panied by the substance of it in print, (say the revievi^ers.) for it is 

 not every one who will be able to decipher it. It runs thus — 



" Oct. 19. When potash was introduced into a tube, having a 

 platina wire attached to it, and fixed into the tube so 

 as to be a conductor, i. e. so as to contain just water 

 enough, though solid, and inserted over mercury, 

 when the platina was made negative, no gas was form- 

 ed, and the mercury became oxidated, and a small quantity of the 

 alkaligen was round the platina wire, as was evident from its quick 

 inflammation by the action of water. When the mercury was made 

 the negative, gas was developed in great quantities from the positive 

 wire, and none from the negative mercury, and this gas proved to be 

 pure Oxygen. — Capital Experiment, proving the decomposition 

 o/ Potash." 



