in the Solar Spectrum. 505 



M. Zaiitedeschi's publication has induced Prof. Ilagona- 

 Scina of Palermo to extend this new field of inquiries. The 

 following are some of the principal results which he has made 

 known*. The horizontal and vertical lines may be perceived 

 by placing a small Galilean telescope against a prism lighted 

 by an aperture of 0""""33. The principal of them may even be 

 seen bj' the naked eye. They likewise exist in the orilinary 

 and extraordinary spectra which a doubly refracting body 

 produces. The horizontal lines may be obtained without the 

 help of a prism, by examining obliquely across a biconcave 

 lens the interval which had remained bright between the two 

 shutters of a window closed to within a decimetref. Lastly, 

 the system of horizontal lines is submitted to an hourly perio- 

 dical return, whilst that of Fraunhofer's lines is perfectly 

 fixed. This assertion is contrary to that of M. Zantedeschi. 



M. Ragona endeavours to explain the lines of Fraunhofer 

 by attributing them to the encroachment of the four simple 

 colours, red, yellow, blue and green. M. Zantedeschi speedily 

 acknowledged himself of this opinion, and also explained, by 

 the reciprocal iiifluence of the luminous rays, his longitudinal 

 lines j. This is proved, according to him, by their appearing 

 so much the more distinct the narrower and longer the spec- 

 trum is; whilst the contrary conditions favour the visibility of 



dc V Acadimie lioyale dcs Sciences de Nancy. We know that Cooper had 

 announced the existence of a visible brightness beyond the red rays (Pro- 

 ceedings of the Royal Society of London, vol. iv. p. 146). The Venetian 

 Professor has not only verified the fact, but he also thinks that he has found 

 an analogous appendage at the opposite extremity. Moreover, the discovery 

 of an extension in the solar spectrum, beyond the violet, is due to Sir John 

 Herschel. He made it as early as 1819, whilst repeating some experiments 

 on the polarized rings with Biot's apparatus ; but he did not describe it till 

 1840, in his beautiful memoir On the Chemical Action of the Rays of the 

 Solar Spectrum on pre[)arations of Silver and other Substances, in the Fhi- 

 loiophical Transactions. In the § 56, entitled " Extension of the Visible 

 Prismatic Spectrum, a new Prismatic Colour," he says expressly that there 

 exists, beyond the violet, some luminous rays of a different coloiufrom that of 

 the different bands of the S[)ectrum, and which is of a lavender-gray. M. 

 Zantedeschi owes to the sky of Venice, which is much more propitious than 

 that of Collingwood, the possibility of studjing this extension of coloration 

 in detail, which will no tloiibt be of some importance in the question of the 

 real number of sim[)le colours, and to which 1 called attention in my me- 

 moir on Daltonism (Taylor's Scientific Memoirs, vol. iv. p. 156). Lastly, 

 tlie author mentions the existence of tints of brigiit blue, visible above 

 and below some prismatic zones of a horizontally jirojected spectrum, and 

 he proposes calling these tints secondury spectra, liut this denomina- 

 tion cannot be adopted, since it has for a lonjj time been applied to the 

 spectra produced by a prism achromatized for the extreme rays. 



* Sutle righe Irasvcrstdi c longitudinnli dcllo spcliro liinnnoso c su lahmi 

 fenomcnli ajjiid. — UiwcoUa Fisico-Chmicn Ilaliana, t. ii. p. 483. 



t It is as well to remark, that the lens performs tiie part of a prism with 

 concave surfaces, with a more or less decided curve. 



I liaccolta, t. ii. p. 507. 



