472 Dr. Frankland on the Blue Band of I he Lithium Spectrum. 



surement. Nevertheless it would be a mere game of intellectual 

 gymnastics to continue such speculations as these ; for reflection 

 on observations made before and since the publication of my 

 letter to Sir John Herschel, leads me to conclude that in the 

 atmosphere of London it is perfectly hopeless to obtain trust- 

 worthy results on this very delicate question. 



For example, my place of observation was Albemarle Street, 

 and my pile when turned on the moon looked nearly due south. 

 The reflector of the instrument thus cleared in a great measure 

 the buildings of Lambeth. I turned the instrument eastward, 

 through a large arc, but in so doing came more over the mass of 

 London. This may account for the diminished loss of heat. 

 But even this, though apparently a natural one enough, I should 

 hesitate to assign as the real cause of the result observed. Fresh 

 experiments, under different conditions, will be required to de- 

 cide the question. 



I may add that I have furnished the pile with a conical reflector 

 of polished tin of vast dimensions, hoping thereby to collect, not 

 only the moon's luminous rays, but also her obscure rays, which 

 even if they reached the earth, were effectually cut off by the 

 polyzonal lens which Melloni used in his experiments on the 

 moon. To protect the exposed face of the pile from currents 

 of air, I have had the reflector furnished with screens of rock-salt. 

 But these precautions led to no satisfactory result, the irregu- 

 larities of the London atmosphere producing disturbances of the 

 galvanometer far more than sufficient to mask the effect of the 

 moon's rays. 



LX. On the Blue Band of the Lithium Spectrum. 

 By Professor Frankland, F.R.S. 



Chemical Theatre, St. Bartholomew's Hospital, E.C., 

 November 7, 1861. 

 My dear Tyndall, 

 N throwing the spectrum of lithium upon the screen yesterday, 

 I was surprised to see a magnificent blue band. At first I thought 

 the chloride of lithium must be adulterated with strontium ; but on 

 testing it with Steinheil's apparatus, it yielded normal results with- 

 out any trace of a blue band. I am just now reading the report of 

 your Discourse in the 'Chemical News,' and I find that you have 

 noticed the same thing. Whence does this blue line arise ? Does it 

 really belong to the lithium, or are the coke-points or ignited air 

 guilty of its production? I find three blue bands with chloride of 

 sodium, but they have not the definiteness and brilliancy of the lithium 

 band. When lithium wire burns in air, it emits a splendid crimson 

 light; plunge it into oxygen, and the light changes to bluish white. 



O 



