320 History of Luminescence 



The Reason hereof very probably is, that the Fire has made this Stone 

 extremely porous, so that among the Parts which are almost wholly dis- 

 joined from each other, there may be some so easy to be put in Motion, 

 that the Light of the Air alone is capable of agitating them; and they 

 may be so disposed to retain this Motion, that they may keep it after 

 they are removed from amongst the luminous Bodies, which put them 

 in Motion; and this is confirmed from hence, that when this Experi- 

 ment is often repeated, these Parts exhale, and the Stone quite loses its 

 shining Quality; which Quality cannot be preserved above four or five 

 Years, though the Stone be carefully shut up in a Box, where no Light 

 can come at it. 



For a farther Confirmation of what has been said, we may observe, 

 that if this Stone be kept too long in the Fire, or though it be kept in 

 it but six Hours, yet if the Fire be very hot, all the Parts of it which 

 cannot resist the Fire, may be carried off, and then the remaining Parts 

 may be so heavy, as not to be shaked by the Light; in which case the 

 Stone ought not to shine, and so we find by Experience. 



Antoine Le Grand presented a typical Cartesian point of view 

 in detail. In his Body of Philosophy (London, 1694) , translated 

 from the Latin of 1680, in speaking of stones which shine in the 

 night (Part II, p. 44) Le Grand wrote: 



We must not imagine, with some, as if the Light of the Sim were pre- 

 served in the foresaid Stone [Bononian phosphor]; forasmuch as that 

 Light, upon the withdrawing of the Sun, doth altogether vanish, as not 

 being able to subsist a moment without its presence; but rather con- 

 clude, that within the Pores, made by the Fire in the said Stone, there 

 be some Fibres, so very moveable, as that upon the presence of the Light 

 they are put into a great agitation, and upon the withdrawing thereof 

 do still continue the motion imprest upon them; and consequently move 

 the surrounding Globuli of the Second Element. And therefore, when 

 either in process of Time, or by the strength of Fire, such Fibres are 

 taken away, that Luminous Virtue immediately vanisheth. The Light 

 of this Stone, as was said, can only be perceived in a Dark Room, because 

 it is very weak, and therefore easily overcome of a stronger Light. As is 

 evident in Rotten-wood, Crickets, and other things that shine in the 

 Night, which by Day give no Light at all. 



The Reason why a Diajnond shines in the Dark, seems to be this, 

 because in the Pores thereof the particles of the 3d Element are so com- 

 prest, that those of the 2d Element being push'd out, some of them are 

 surrounded only with the 1st Element, by which they are carried away, 

 and the Globuli are driven or push'd forwards. 



