148 Notices respecting New Boohs. 



" spectre solaire " shows it as a wide hazy filled-up double. We 

 note here the widening and filling-up of M. Pievez's doubles ; and 

 on page 17 are curious instances of the fact that spectroscopic 

 power does not necessarily imply fine definition. Where Prof. 

 Young with a single Rutherford grating saw 27 thin lines, M. 

 Pievez, with a similar grating and two Christie half-prisms added, 

 saw only 13. Prof. Young has also one more strong line split into 

 two than M. Pievez ; and in matter of doubles shown to be triples, 

 the former has one which the latter has not. 



Subjects 16 and 17, Plates XIII. and XIV., relate respectively 

 to the bandelet of lines following E, and to a " basic " line prece- 

 ding " little b." In the latter subject we again find a single line of 



o 



Angstrom's, of Kirchhoff and Hof mann's, and even of Vogel's map, 

 beautifully split by our author and by M. Pievez, the line itself 

 being left to imagination in the Royal Society's map. 



The " little b " (magnesium) group comes next, in subject 18, 

 Plate XV., with a repetition in b l , b 2 , and b 4 of the pale and hazy 

 effects shown in Great C and D (indicative of the volatility of mag- 

 nesium to solar heat) in Vogel's, the author's, and M. Pievez's 



o 



maps, b 4 , a single line by Angstrom attributed to Mg and Pe, 

 remains single in the earlier maps, including Vogel's, but is well 

 divided by the author and M. Pievez ; while the latter seems also 



o 



to have divided b 3 , marked M and Pe by Angstrom, and retained 

 as single even in the Madeiran spectrum. In Plate XVI., sub- 

 ject 19, a group following " little b," we get three basic lines of 



Angstrom's, all marked Pe and Ni, neatly divided by the author 

 and M. Pievez, they making a triple of one of Vogel's doubles. 



Plate XVI., subject 20, is Great P, with the paleness and haze 

 characteristic of a solar storm-line (duly recorded, by the way, by 



o 



Angstrom). The comparative effect of eye and photographic 

 brightness as between the glaucous and violet hydrogen-lines is here 

 discussed. 



"Near G" line or violet hydrogen, Plate XVIL, subject 21, ends 

 the typical series with further illustrations of the hydrogen haze 

 and paleness. 



Example 4 on Plate XVIL gives us the interesting part of the 

 spectrum adjoining " near G " as shown in Rutherford's photo- 

 graph ; and it is noteworthy how closely this absolute reproductioo 

 corresponds with the Madeiran hand-drawn spectra. 



If we were aesthetically startled by the black and white of Plates 

 I. to XVIL, Plate XVIII. effectually consoles us ; for, without 

 exception, we have seen no specimen of chromo-lithography to 

 compare with it for brilliancy and blending of tints. It does the 

 greatest credit alike to the author's artistic conception and to the 

 lithographer's skill. It represents three diagrams of colours on 

 spectrum principles : — (1) Pure or single spectrum colours in 

 their natural order ; (2) mixed or double spectrum colours ; and 

 (3) very mixed or treble spectrum colours. The diagrams most 



