Intense Light visible at great Distances. 321 



sides. By these means every requisite adjustment is obtained 

 for the jets through which the gas issues. The apparatus is 

 attached by its base to the stand which carries the reflector, 

 (Fig. 1. Plate VIII. ;) and the small ball may then, by 

 means of the horizontal and vertical screws r, be brought with 

 great accuracy into the focus of the reflector. The cistern c 

 containing the alcohol is placed behind the reflector, (Fig. ] ;) 

 and being connected with the stem a by a flexible caoutchouc 

 tube, may be elevated or depressed on the upright rod r, 

 Fig. 2, and the flame of the spirit, accordingly, regulated so 

 as to produce the greatest effect. A flexible tube leads from 

 d to the vessel containg the oxygen, which may be either a 

 common gas-holder, or, perhaps, a silk bag, with a layer of 

 caoutchouc, such as they are now made, might be convenient- 

 ly employed for this purpose. The apparatus first made was 

 provided with Jive jets, and could light up a ball | inch in 

 diameter ; that now represented has only three, and with it a 

 ball j of an inch in diameter may be used sufficiently large to 

 admit of the requisite allowance being made for aberration 

 in the reflector, from its true figure, as well as uncertainty of 

 direction, arising from terrestrial refraction. 



" To ascertain the relative intensities of the different in- 

 candescent substances that might be employed, they were re- 

 ferred by the method of shadows to an argand lamp, as a 

 common standard, the light from the brightest part of the 

 flame being transmitted through apertures equal in diameter 

 to the small spheres of the different substances submitted to 

 experiment. 



" The results of several trials made at the commencement, 



gave for 



Lime, 37 times 



Zirconia, - - - 31 times 



Magnesia, - - - 16 times 



the intensity of an argand burner. The oxide of zinc was 

 also tried ; but, besides wasting away rapidly, it proved infe- 

 rior even to magnesia. 



" The mean of ten experiments, made lately with every pre- 

 caution, gives, for the light emitted by lime, eighty-three times 

 the intensity of the brightest part of the Same <>f an argand 



