400 Original Articles. [July, 



Mr. Kutherfurd has also taken photographs of the solar spectrum 

 on the same scale as the map of Kirchhoff, but no detailed account 

 has as yet been published. His other labours in celestial photography, 

 and more particularly his lunar pictures, are so well known that no 

 description of them is necessary. 



Professor Hood's Experiments. — In ' Silliman's Journal,' No. C, 

 for 1862, there are some facts concerning the spectrum afforded by 

 nitrate of didymium. Gladstone had originally found that light, 

 transmitted through dilute solutions of this salt, showed two dark 

 lines in its spectrum. Professor Rood, on causing the light to go 

 through a thickness of 12 inches of a strong solution, found that the 

 spectrum was crossed by twelve distinct bands. The sodium line is 

 cut off by one of these bands, and hence a sodium flame is invisible 

 through this solution, though white objects are but slightly tinted. 



In No. CI., for 1862, Professor Eood describes his spectroscope 

 with four prisms, three of bisulphide of carbon and one of flint glass. 

 He points out a method of avoiding the curvature of the plane glass 

 sides of such prisms, by covering each with a second plane and 

 parallel sided plate, a few drops of olive oil being placed between. 

 With this spectroscope, he found two new lines in the interior of the 

 line D, making three fine lines enclosed in that double line. 



In No. CV., for 1863, he points out the advantages of the bisul- 

 phide of carbon prism, as compared with the flint prism, an instru- 

 ment by Merz, the sum of whose refracting angles was 270°, being 

 unable to resolve the line D as completely as one consisting of three 

 bisulphide of carbon prisms of 60° and one flint of 45°, though the 

 sum of the refracting angles was 45° greater. He also insists on the 

 advantage of large aperture. 



Professor Cooke's Experiments. — In ' Silliman's Journal,' No. CI., 

 for 1862, the prism made for Professor Cooke, by Clark, is described. 

 It is built up of several thicknesses of plate glass, cemented together 

 with Canada balsam. He describes its defining power, and the ap- 

 pearances presented by the orange band of strontium. It consists of 

 an orange space covered by a large number of black lines, similar to 

 those of Fraunhofer. 



In No. CVII., for 1863, Professor Cooke describes a spectroscope, 

 the largest made up to that time. It has nine prisms of bisulphide 

 of carbon, giving 2j inches aperture, with telescopes of corresponding 

 size. The prisms are made on Rood's plan. The instrument has 

 established the following points : — 1st. That the lines of the solar 

 spectrum are innumerable ; it shows at least ten times as many as are 

 given by Kirchhoff, with very many nebulous bands on the point of 

 being resolved ; the line D consists of nine lines, and a nebulous band. 

 2nd. That the coincidences of the bright lines of metallic spectra, and 

 the dark lines of the solar spectrum, remain perfect even with this 

 increased power. 3rd. That many of the bands of metallic spectra 

 are broad-coloured spaces, crossed by bright lines. This is the case 

 with the orange band of strontium, and with the whole of the calcium 

 and barium spectra. 



Messrs. Johnston and Aliens Experiments.' — In No. C1II. of ' Silli- 

 man's Journal,' for 1863, they describe the spectrum of cassium, 



