Page:Various Forces of Matter.djvu/180

168 earnestly and carefully in favour of the electric light.

I am going to show you the effect that will take place with that large lens when we throw the oil lamp out of action, and put the electric light into use. It is astonishing to find how little the eye can compare the relative intensities of two lights; look at that screen and try to recollect the amount of light thrown upon it from the 3¾ inch lamp of Fresnel, and now, when we shift the lens sideways, look at the glorious light arising from that small carbon point (fig. 58); see how beautifully it shines in

the focus of that lens and throws the rays forward. At present the electric light is put at just the same distance as the oil light, and therefore, being in the focus of the lens, we