J)KVEL()1'MENT OF ILLUMINATION. 4^,)5 



liulit from a ciuulh* or otlicr cominoii illimiiiiaiit. 'riiat the lio-ht is 

 a choinical jn-oduct would simmu to !>(> cstahlislicd hy the fai-t that 

 it decreases by ])roducts whieii cluHdc (•onil)Ustioii {v. o-., iiitroo-en) 

 and increases bv products which aid combustion (oxyo-en), and tliat 

 tlie pi'oduct of the process is apparently carbon dioxich*. 'Ilu' sul)ject 

 of tile orig'in of 'phosphorescent*' lioht is one that may (leveh)p very 

 interesting- features, for, as oraphically stated ))y Prof. Oliver J. 

 Lodye, if the secret of the lireHy were known, a boy turnini;- ji crank 

 niiiiht l)e al)l(> to furnish the enero-y necessary to lioht an entire elec- 

 tric circuit. From this standpoint Professor Lodye re<;ards as enor- 

 mous the Avaste of enerjLiy in the machinery of eh?ctric-lii>;ht making 

 now in use.'' 



Most of the 15<> s])ecies of animals which are lio'ht-])roducing iidiabit 

 the sea, where their light is of small importance to man. The wonder- 

 ful phosphorescence of the tropical seas, which has drawn forth many 

 descriptions of its beauty, is caused by the collective lights of myriads 

 of infusoria} on the surface of the water. 



The day opens up a vast field of activities requiring light for their 

 prosecution. Solar light is normal for the carrying on of these activi- 

 ties, and the night is normal for rest and recuperative processes. The 

 important phenomena of the day are sunrise and sunset; and the da^^'s 

 Ial)or regulates itself to twilight, morning and evening hours, and the 

 hours of l)road day divided })}' the meridian of the sun. Sunrise is 

 attended with certain phenomena, which observant people have noticed. 



The Hopi tribe of Arizona, for instance, emplo}^ the following terms 

 for sunrise: Sunrise, talavaiya; place of sunrise, taam yum tiiahJ ; 

 faintest dawn, liu/nnqytil; first light, taltl\ light of sunrise, tuld'n'c; 

 yellow light of sunrise, xihyanilptu; before emergence of sun, tawa 

 I'iiyini^ '"sun appears;" sunup, tawa yama.'^ Few tribes indeed have 

 not Ijeen impressed with dawn and sunset, and few in the obli(jue lati- 

 tudes have failed to mark the seasonal progress of the sun along the 

 horizon. 



There is a wide difi'erence in the amount of sunlight enjo3'ed by the 

 dwellers on the earth's surface, depending on the height and configu- 

 ration of the land, its absorptive and reflective qualities, the presence 

 of forests and vegetation, the amount of moisture and dust in the air, 

 cloud formation, and other elements which suggest themselves to the 

 reader, producing local and pei'iodical variation. To these must be 

 added the seasons and the position in latitude determining the length 

 of the day and the duration of twilight. 



The superabundanc(> of suidight has brought about many devices 

 for warding ott' and tempering the rays and amelioi'ating their heat. 

 For protecting his eyes from the excessive light man has devised e3'^e- 

 shades, hats, and parasols; and for shade and protection from the heat, 



Authoritv of Dr. .J. Walter Fewkes. 



