Dr. C. K. Akin on Calcescence, 31 



true whenever the incident rays are Ritteric ones, the presump- 

 tion has arisen that only such transmutations may actually occur 

 in nature as involve a decrease of refrangibility in the emitted 

 ray as compared with the incident. If such were the case, it is 

 evident that the species of transmutations instanced above from 

 under (1) to (6) would alone be possible, whilst the remainder 

 would be impossible by the nature of things. Among the 

 transmutations the possibility of which is thus more or less 

 directly negatived, the species (8) and (10), forming in some 

 sense the counterpart of those properly comprised under fluores- 

 cence and phosphorescence (namely of (2) and of (4)), it would 

 undoubtedly be of the greatest importance to effect. A simple 

 consideration of well-known facts will show that the transmu- 

 tations (8) and (10) may probably be effected. 

 . 5. Calcescence. — The metals, by Professor Stokes, are classed 

 among non-fluorescent substances*, and by M. E. Becquerel, to 

 whom, as is well known, the most delicate observations on phos- 

 phorescence are due, among non-phosphorescent substancesf — 

 Professor Stokes having been unable to elicit Newtonic rays from 

 metals by the means found efficient with fluorescent substances, 

 and M. Becquerel having been unable to detect any persistency 

 of luminosity in metals exposed to the treatment of the phospho- 

 roscope. On the other hand, it is well known that metals may 

 be rendered self-luminous or incandescent by contact with flames 

 of high temperature, by electrical and other means ; and, though 

 no experiment appears to be on record affording clear evidence 

 of the fact, it is impossible to doubt that the same effect might 

 also be produced by solar radiation of sufficient intensity. If 

 this latter assertion be founded on truth, it must be evident that 

 all metals, in the wide sense of the word, are fluorescent, and 

 most probably also phosphorescent ; for of these phenomena no 

 other definition can for the present be given than that of an 

 emission by renovation of luminous rays on the part of sub- 

 stances irradiated from without, which would clearly be appli- 

 cable to the case of any metal rendered incandescent by means 

 of insolation. Or, if the definitions of fluorescence and phos- 

 phorescence be restricted so as to apply only to facts of the same 

 order as hitherto discovered, namely, to emissions by renovation 

 of luminous or Newtonic rays, on or after incidence of either 

 Newtonic or Ritteric rays 3 even in that case it may be shown 

 that the metals have a claim to be classed among fluorescent, 

 and then most probably also among phosphorescent substances. 

 Every kind of radiation possesses, with respect to any given 



* Phil. Trans, for 1852, p. 516— "Metals proved totally insensible." 

 f Ann. de Chini. et de Phys. vol. lvii. p. 45 (1859) — "Les metaux n'ont 

 donne jusqu'ici aucun effet appreciable." 



