CHAPTER II. 



THE OPTICAL SYSTEM OF THE LANTERN. 



jHE three great essentials of a good optical lantern 

 are the light, the condenser, and the objective, the 

 two latter forming the optical system of the instru- 

 ment. Theoretically, the light to give the best results should 

 be a mere point of radiance, but unfortunately this is 

 at present almost unattainable. I say almost, because I 

 believe it to be quite within the bounds of possibility to con- 

 struct an electric arc light which shall fulfil all the conditions 

 as to steadiness, uniformity of action, and maintenance of 

 a fixed position, which are required in lantern work. Such 

 a light has not yet been found, but when electricity 

 becomes more general as a source of illumination in our 

 cities and towns, as it .surely will, an arc light or 

 regulator of the required description will, I feel confident, 

 soon be forthcoming. The invention of such a con- 

 trivance, when the means of obtaining the requisite 

 current to feed it is so limited, would at present have the 

 disadvantage of coming before its time. The electric 

 arc light has been used more than once experimentally 

 in the lantern, with the most promising results. 



