0% fttiwnfct ' 209 



j?ou will Consider only an tfie rudiment* t>£ ideas, which ob- 

 servation and reflection may perha;^ herrufteijeoniiriori. 



I have laid it down as a principle, that the li<>/tt which Their light is 

 h i i • i )• i /•"" # from some che* 



emanates irom phosphoric bodieB can arise only jroui a tie* mxCiX \ decom- 



iomposition, which liberates this light from its combination portion, 

 with other ingredients, and which must be induced and in- 

 fluenced by preceding chemical actions on these bodies. 

 This general principle is deduced from, the experience of all 

 the luminous phenomena, that are exhibited in our chemi- 

 cal processes, and all that we observe to take place sponta- 

 neously on our globe: ami this is all we can refer to the 

 other large bodies in the decreasing scale of these effects, 

 from the Sun and fixed stars, the light of which is so in- 

 tense and permanent, to the phosphoric phenomena of our 

 atmosphere. Thus we can determine nothing with respect of the natureof 



to the constitution of these bodies, the nature of the che- wh ic. hw eknov» 



nothing. 

 mical processes that extricate light from them, the periods 



in which these effects must be reproduced, or lastly their 



different appearances when they are produced. Here then 



we tind many causes of uncertainty in the application of 



this principle to the phenomena of comets; and accordingly 



every thing I have to say on the subject must be vague and 



hypothetical. ♦ 



I conceive, that a great number of bodies revolve round Small bodies 

 the Sun at cjjfferent distances, and with different motions ; revolve round 

 which from the smallness of their size, and more especially ^nfiw vSe 

 from the nature of their surface, cannot be rendered, visi- 

 ble to us by reflection of the solar rays ; but which at cer- 

 tain times, or under certain circumstances* are capable of 

 producing luciferous vapours. 



Let us suppose, that a certain degree of proximity to the their luml- 

 Sun is a circumstance determining either the production or nousnes? Ms 

 the decomposition of these vapours; in other words, that ueames/to the 

 the intensity of its ra#€ is the chemical cause, that induces Sun - 

 the luminous effects. I have been led to this idea by a Phenomena of 

 phenomenon observed in our experiments, which displays th e Bolognian 

 some analogy with the supposition here made : certaiu bo- P hos ^ horul » 

 dies recently calcined, or calcined anew, such as oyster 

 shells and the Bononian stone, after having been some time 

 exposed to the rays of the Sun, are luminous in the dark* 



Vol. XXII— March, I809. P JEuler 



