Notices respecting New Books. 145 



discriminating and faithful in reproducing lines, bands, sha- 

 dows, &c. 



(6) Janssen's copperplate prismatic spectrum from C to D 

 (about 1874). Very accurate, almost microscopic. 



(7) The Royal Society's prismatic second Himalaya spectrum, by 

 Hennessey, in Phil. Trans. 1875. On stone, mechanical but cer- 

 tain, with the merit of showing high- and low-sun spectrum from 

 the ultra-red to Great P. 



(8) Captain Abney's drawing from his remarkable photographs 

 of the ultra-red region beyond the range of optical vision (grating), 

 1878. 



(9) Prof. Langley's lithographic views of Great A and Great B 

 (1878). 



(10) M. Pievez's engraving on stone of a grating-spectrum of the 

 little "6" group (1880). 



(11) Prof. Vogel's Potsdam prismatic- spectrum map from near 



E to K, on three times the scale of Angstrom's map, part based on 

 eye-observation and part on photographs (1880). 



(12) Lastly, Prof. Young's pencil-sketch of the Great E group 9 



on nine times the scale of Angstrom's normal map. A most refined 

 and exact drawing from a fine grating (1881). 



Later on (1882) the author received a copy of M. Pievez's grand 

 " Spectre Solaire " (obtained with a Rutherford grating and two 

 Christie half -prisms), and substituted its results for some of his 

 Madeiran duplicates. 



Part II. opens by describing the frontispiece plate (0) as containing 

 three spectrum-scales, the British inch being used in these and the 

 other spectrum-plates as the unit. Porm 1 is a wsive-number shape, 

 with about equal portions of the red and violet ends. Porm 2 a 

 wswe-length shape diffraction (grating) spectrum, with much red 

 and a contracted violet. Porm 3 an average refraction (prism) 

 spectrum, showing a contracted red and opened-out violet. 



We now proceed to the 21 subjects and their 147 examples, 

 which we can but notice briefly, though each of them contains some 

 interesting, and often novel, feature. 



Plate I., subject 1, Great A. We first get an explanation that a 

 perfect reproduction of the exquisite lines and shadows seen in the 

 solar spectrum is difficult to impossibility, and a pointing-out that 

 the shading by vertical lines generally adopted by lithographers 

 and engravers is mischievous and deceiving. 



Prof. Smyth then lays down as rules : — 



1st. Any vertical line shall represent a true spectrum-line and 

 nothing else. 



2nd. Greater or less thickness of lines shall be represented truly ; 

 but degrees of intensity by shortening the height of column, or (less 

 easily) by dotting, stippling, or crossline. 



3rd. Thin hazy lines by vertically dotted or vertical linearly wavy 

 lines ; or such shorter figurings in ink as would, if smeared verti- 

 cally, produce a correspondingly pale line. 



