396 



NATURE 



[Sept. 17, 1874 



years an ample supply of those who prefer to remain 

 ignorant and uncultured to satisfy all demands. In 

 the noble address delivered by Prof. Huxley at Belfast, 

 he insisted, with all the force of his calm eloquence, on 

 the folly of making a bugbear of logical consequences ; 

 and in no science is there more need for this exhortation 

 than in that of education. Mrs. Grey well put it that no 

 education is worthy of the name that does not at least 

 aim at a right training of the three departments of the 

 mind — the reasoning faculties to determine the right from 

 the wrong, the emotional to follow the right when found, 

 and the imaginative to conceive the perfect ideal of all 

 goodness. In determining a course of education, whether 

 for boys or girls, when we have once satisfied ourselves 

 that our principles are sound, let us unhesitatingly follow 

 them cut, letting the possible consequences take care of 

 themselves ; and we may feel sure that the conclusions to 

 which we shall be led will stand the test of experience. 



The point which we think should be most prominently 

 brought forward by the advocates of a reform in female 

 education is not so much the desirableness of turning its 

 future current in any one direction, as the necessity for 

 removing all trammels and barriers raised by man's igno- 

 rance or prejudice. On this ground we sympathise most 

 heartily in all the efforts now being made to widen the 

 basis of the education of women, whether in the way of 

 special colleges, university examinations, or courses of 

 lectures involving severe study. Let us first of all — divest- 

 ing ourselves of all preconceived theories on the subject, 

 whether social, metaphysical, or physiological — give free 

 scope to the faculties of woman before we begin to dog- 

 matise on the extent to which these faculties will bear 

 cultivation. Natural Selection will point out the occu- 

 pations in which the female mind will excel ; and the 

 Survival of the Fittest will determine the professions in 

 which woman can successfully compete with man. And 

 every one who believes that faculties were originally 

 endowed or gradually evolved for the purpose of being 

 used, and powers for the sake of being exercised, must 

 rejoice at every fresh extension of the field in which they 

 may be employed. 



DE 



BOISBAUDRAN ON 

 LUMINEUX 



SPECTRES 



Spectres Prismatiqucs et en Longticurs d'Ondes destines 

 aiix Rccherchcs de Chimie Mincrah. Par M. Lecoq 

 de Boisbaudran, avec Atlas des .Spectres. (Paris: 

 Gauthier-Villars, 1874). 



THE spectrum maps of Kirchhoff, Huggins, Angstrom, 

 and Thalcn are so complete that little has been 

 left for later observers except the filling up of some de- 

 tails. Angstrom's discovery that the bright lines which 

 form the spectrum of the electric spark are partly due to 

 the air or other gaseous medium traversed by the spark, 

 prrtly to the vapour of the metallic poles, formed an 

 epoch in the history of spectrum analysis ; and the publi- 

 cation of the fine map of the solar spectrum by Kirchhoff 

 (founded on the great original work of Fraunhofcr), in 

 which the positions of a large number of the metallic lines 

 arc carefully laid down, gave a great impulse to the pur- 

 suit of this branch of physical science. For the discovery 

 of the new metals, caesium, rubidium, thallium, and 



indium, we are indebted to spectroscopic analysis. In a 

 paper communicated to the Royal Society in 1863, Mr. 

 Huggins gave a valuable map of the bright lines of the 

 metals, as seen through a system of prisms adjusted for 

 a minimum deviation of the line D of Fraunhofer. 

 This was followed by the works of Thalen and Mascart, 

 in which the po;itions of the metal lines are given in 

 wave-lengths. The results obtained by Thalen are incor- 

 porated in the great work of Angstro.-n on the solar 

 spectrum. 



To observe the metal line?, the method usually em- 

 ployed is to pass the spark from a Ruhmkorffs machine, 

 having a condenser connected with the fine wire, between 

 poles of different metals. The air lines which come into 

 view at the same time are easily distinguished by well- 

 known characters from the metal lines, and were used by 

 Mr. Huggins to fix the positions of the latter. In some 

 cases the metal lines were obtained by drawing sparks 

 from solutions of the chlorides. 



In the work of M. Lecoq de Boisbaudran, two methods 

 are chiefly followed for obtaining the spectra of the 

 elements and of certain compound bodies. The first is 

 the ordinary method of heating the body in the flame of 

 a Bunsen burner ; the second is to pass short electrical 

 sparks from a Ruhmkorff's coil, without condenser, be- 

 tween a solution of the chloride of the metal and a fine 

 platinum wire suspended above the solution. In the latter 

 case the following is the method of experimenting usually 

 employed by him : — The metallic solution is contained in 

 a short glass tube, into the lower end of which a platinum 

 wire is hermetically sealed. Another wire of platinum, 

 or, still better, of iridium, attached to an insulating sup- 

 port, is adjusted at a distance of two or three milli- 

 metres from the surface of the liquid. An essential con- 

 dition to the success of the experiment is to make the 

 free wire positive, and the liquid negative. If this 

 condition is reversed, the spectrum of the solution seldom 

 appears, but is replaced by the ordinary air spectrum. In 

 some cases, as with the alkaline salts, a fine spectrum is 

 obtained by passing sparks between a fused bead of the 

 salt and a platinum wire heated to redness in a Bunsen 

 or spirit flame. According to M. Lecoq de Boisbaudran, 

 the spectrum produced in this way is not only more 

 brilliant, but is richer in metallic lines than that of the 

 solution. The method of taking sparks in air between 

 metallic poles has been employed in the work before 

 us only in the cases of aluminium and lead. The spectro- 

 scope employed was formed of a single prism of heavy 

 gla5s, with a collimator, and telescope moveable on a 

 graduated arc. An illuminated scale, projected from the 

 anterior surface of the prism, was seen above the spec- 

 trum, and its indications were reduced to wave-lengths by 

 comparison with the wave-lengths of certain solar and 

 metallic lines, as determined by Fraunhofer, Mascart, 

 Angstrom, and Thalen. 



In a scries of twenty-eight finely-cxeculcd engravings, 

 M. Lecoq de Boisbaudran has given delineations of the 

 spectra of a large number of bodies referred to the aibi- 

 trary scale of his spectroscope, and also in wave-lengths. 

 Except in a few cases, he has not attempted to represent 

 the feebly illuminated ground or continuous spectrum 

 which in many instances extends over nearly the whole 

 field of view. But the characters of the bright lines and 



