8 On Phosphorescence. 



four or five electrical discharges. This method equally 

 succeeds with every substance which has lost its phos- 

 phorescence by calcination. There is not even a necessity 

 for a discharge, and we restore phosphorescency to calcined 

 adular, for example, by a simple current of electricity de- 

 termined by a conductor terminated in a point, and which 

 is passed through this substance reduced to a liquid paste, 

 with a quantity of water sufficient for leaving an easy pas- 

 sage to the electric fluid. After three or four minutes of 

 electrization, this paste, afterwards dried spontaneously, 

 yielded a very phosphorescent powder on the hot supporter. 

 What is most remarkable in this way of restoring phos- 

 phorescence to bodies which have lost it by calcination, is, 

 that it never reestablishes it in those which have been de- 

 prived of it by exposure to the light of the sun. 



The third chapter of M. Dessaignes' memoir contains 

 his inquiries as to the phosphorescence produced by light or 

 by electricity. He first refutes the opinion of a great num- 

 ber of persons, as to the cause of the lustre which is pre- 

 served during a longer or shorter period by bodies exposed 

 to the light of the sun. The sulphuret of lime, known by 

 the name of Canlon phosphorus, the dried nitrate of lime, 

 clucine and Bologna phosphorus, after having been hit 

 bv red ravs onlv, shone with precisely the same yellow, 

 white, green, and reddish colours which they afforded when 

 exposed to the ordinary light of the sun. The same thing 

 took place after their exposure to the light of each ray of 

 the solar spectrum, or to that of coloured flames; and what 

 confirms the idea that ihcse phaenomena are not owing, as 

 has been supposed, to the imbibition of light by the phos- 

 ohorcsccnt substance, is, that the Canton phosphorus pre- 

 pared wiihout having experienced in any shape the contact 

 of lisht, shines equaUy upon a heated supporter, or even by 

 the simple heat of the hand. This phosphorus shines, on 

 exposure to the light of the moon or to that of a lamp. 

 The light of the moon is not sufficient for Bologna phos- 

 nhorus, which takes fire, however, on being exposed to the 

 hoht of a lamp with a stream of air. Most of the other 

 phosphorescent substances require the light of the sun. It 

 IS sufficient, even after having been reflected, for several 

 salts : but cat'i eye, hyoline quartz, and phosphate of 

 P'.siremadura lime do not shine until after having b^en ex- 

 posed to the du-ect light. Other substances, such as zircon, 

 nibv, cymophanc, and other vitreous stones, absolutely re- 

 «:i«t the action of the light even when it is concentrated in 

 the focuti of a. burning mirror. 



The 



