78 Mr Talbot's Experiments on Coloured Flames. 



cohol, diluted with water, consists chiefly of homogeneous yel- 

 low rays. On this principle, he proposed the construction of 

 a monochromatic lamp, and pointed out its advantages for ob- 

 servations with the microscope. This must be considered a 

 very valuable discovery. The light of such a lamp, however, 

 is weak, unless the alcohol flame is very large. I have, there- 

 fore, made several attempts to obtain a brighter light, and I 

 think the following is the most convenient method. A cot- 

 ton wick is soaked in a solution of salt, and when dried, 

 placed in a spirit lamp. It gives an abundance of yellow 

 light for a long time. A lamp with ten of these wicks gave 

 a light little inferior to a wax candle ; its effect upon all sur- 

 rounding objects was very remarkable, especially upon such as 

 were red, which became of different shades of brown and dull 

 yellow. A scarlet poppy was changed to yellow, and the 

 beautiful red flower of the Lobelia J'ulgens appeared entirely 

 black. The wicks were arranged in a line, in order to unite 

 their effect for a microscope. A common blue glass has the 

 property of absorbing the yellow light of this lamp, however 

 brilliant, while it transmits the feeble violet rays. If these 

 are also stopped by a pale yellow glass, the lamp becomes 

 absolutely invisible, though a candle is seen distinctly through 

 the same glasses. But the most remarkable quality of this 

 light is its homogeneity, which is perfect as far as I have 

 been able to ascertain. I speak of the yellow rays, which 

 form the mass of the light, and quite overpower the feeble 

 effect of the blue and green. The origin of this homogeneous 

 light appears to me difficult to explain. I have found that 

 the same effect takes place whether the wick of the lamp is 

 steeped in the muriate, sulphate, or carbonate of soda, while 

 the nitrate, chlorate, sulphate, and carbonate of potash, agree 

 in giving a blueish white tinge to the flame. Hence, the 

 yellow rays may indicate the presence of soda, but they, never- 

 theless, frequently appear where no soda can be supposed to 

 be present. 



2. Mr Herschel discovered that sulphur, when burning in- 

 tensely, gives a homogeneous yellow light. To examine it, I 

 inflame a mixture of sulphur and nitre behind a screen, hav- 

 ing a narrow vertical slit through which the flame could be 

 seen. This opening, examined with a prism, gave a spectrum 



