42 C. PIAZZI SMYTH ON THE 



field, together with the Sun spectrum ; but behold, although it was much 

 clearer than the little I s Nickel line, it was yet a very poor thing ; so poor, that 

 I wandered off into the Citron regions, amongst the groves of hazy air lines, to 

 see if something better could not be found there ; and sure enough I stumbled 

 almost immediately on a magnificent line, a line which for brightness, beauty 

 and definition was far beyond everything else in the field of view, though that 

 was a pretty full one too. It proved to be the line at 46 380 W.N. Place, which 

 Dr Watts has entered in his tables on the authority of both Thalen and 

 Kirchoff as of intensity only equal to 6, when the trifling line between D 1 and 

 D 2 was called by them 10. 



On turning to Angstrom's Normal Solar map with its chemical references, 

 I was encouraged by finding the D Nickel line and its Solar representative also, 

 far fainter than the 46 380 W.N. line of Nickel and its Solar reversal. But on 

 still further referring to that most able observer M. Lecoq de Boisbaudran, he 

 represents the 46 380 line, as the very maximum, or the a, of the whole Nickel 

 spectrum ; gives no place to the D Nickel line at all ; and only the faintest 

 imaginable marking to the Nickel line in the place of b 3 . His deflagrating 

 method was however different ; for he used simple, uncondensed electric sparks, 

 and employed them not on metal points, but on a solution of a salt of the 

 metal. Perhaps too, bearing in mind the extreme modesty of his " spectro- 

 scopic installation," it is wrong to refer to him, — master hand though he 

 undoubtedly is, so far as it accords with his plan to go into any subject, — for 

 more than the testimony he gives to the magnificent lustre of the a line at 

 46 380 W.N. Place. So that the only remaining anomaly, but a most important 

 one, to be cleared up by those who have plenty of electrical energy at their 

 command and a good spectroscope, is, the immense intensity attributed to the 

 D Nickel line by MM. Thalen, Kirchoff and Watts ! Is there a numerical 

 error there, or is that line capable of peculiar intensification with increased 

 electric temperature % 



But meanwhile though I may have failed in that inquiry, what an extension 

 of the powers of pure and simple spectroscopic observation (when we have 

 light enough) does not the new College Spectroscope already exhibit ! 



A few years ago some of our best men thought the ne-plus-ultra of accurate 

 observing had already been reached with the Dispersion of a single prism of 60° 

 and magnifying power on a telescope of about 20 : for after that, they found 

 that whatever was gained in Dispersion by adding a second or third prism, was 

 lost by bad definition. But here, thanks to the super-excellence of our British 

 optical house, Messrs T. Cooke & Sons of York, no less than 20 prisms are 

 virtually employed, and the limits of fine definition, even when tested by high 

 magnifying power, are not yet reached. 



All that Dispersive power too, and all that Definition are perfectly necessary 



