SciEXTiFic Lectures. 131 



that produce that beautiful result of fluorescence, all required to be 

 liarmonized to produce that light which ^\e see by day, and which we 

 also see reflected from the moon bv night. Let us not forget what 

 we were taught in early childhood, found in the first simple rliymelets 

 that we ever harmonize and study to memorize, from Mother Goose's 

 simple story: 



" A twister in twisting would twist him a twist, 

 And twisting his twist, seven twists he doth twist ; 

 If one twist in twisting untwists from the twist, 

 The twist, untwisting, imtwists from the twist." , 



The same has been thus happily paraphased : 



" A raveled rainbow overhead, , 



Lets down to life its varying thread ; 

 Love's blue, Joy's gold, and fair between, 

 Hope's shifting light of emerald green, 

 With either side, in deep relief, 

 A crimson Pain, a violet Grief 

 "Would'st thou, amid their gleaming hues. 

 Clutch after those, and these refuse ? 

 Believe, as thy beseeching eyes 

 Follow their lines, and sound the skies, 

 There, where the fadeless glories shine, 

 An unseen angel twists the twine ; 

 And be thou sure what tint soe'er 

 The broken rays beneath may wear. 

 It needs them all, that broad and white, 

 God's love may weave the perfect light" 



At a glance you perceive what an extended theme is offered for 

 the limits of a lecture, and what suggestions naturally fill the mind 

 of a thinking being. If the Almighty has created such realms of 

 space, such systems of worlds, whole oceans of suns, and beyond 

 these, nebulge, which, in their hazy condition, as the spectroscope has 

 demonstrated, are yet unformed worlds, how the mind is lost. And 

 when we with wings of light, which are leaden in comparison with 

 the wings of imagination, pass from universe to universe, until we 

 sink exhausted — it is but the beorinning of the end. - 



But I propose, instead of presenting this in its vast field and in its 

 poetic relations — because there is poetry as well as solid facta in 

 science — to come down to three simple points : 1st, How do we 

 produce light i 2d, Of what is light constituted \ and 3d, How do 

 we measure it ? 



We produce light first, by the production of heat. Before you is a 



