2io Mr. Morgan’s Obfervattons and Experiments on 
may be made as luminous as ever by expofure to the fun. But 
3°. It is observable, that fome bodies, which are mod; beau- 
tifully phofphoric, or which, according to Mr. Wilson’s 
theory, are in the bed; ftrte of flow combuflion ; It is obfervable, 
I fay, that the fame bodies are the mod: obftinate in refilling the 
fire. The diamond, which to be decompafed requires the 
force of a. mold powerful furnace, is, according to this 
theory, waffing away, owing to a reparation of parts which 
Is promoted by the weakefl influence of the fun’s rays. — With- 
out determining whether the preceding objections be valid, let us 
now fee the confequence of admitting the common hypotheds, 
that the detention of thofe rays which fall upon phofphori is 
owing to fome force which prevents their immediate reflection, 
but is not adequate to their entire abforption. This force, 
whatever it be, cannot well be fuppofed to operate with equal 
power on all the rays. And if this be not the cafe, I think 
we cannot avoid concluding, that phofphoric fhells will aflfume 
different colours, owing to the earlier and later efcape of the 
different rays of light. This concludon is juftided by an expe- 
riment which I have already appealed to. When the force is 
fuch as to admit of the efcape of the purple, the blue, and the 
green, we have only to leffen that force by warming the body;, 
and the yellow, the orange, and red efcape. It is proved by 
Becc aria’s extenfive experience on this fubjcCt, that there is 
fcarcely any body which is not phofphoric, or which may not 
be made fo by heat. But as the phofphoric force is mod; 
powerful when the purple rays only efcape, fo we are to con- 
clude, that it is weakeft when it is able to retain the red rays only. 
This concludon is agreeable to feYeral faCls. Chalk, oyffer- 
%lis, together with thole phofphoric bodies whofe goodnefs 
