214 Notices respecting Neio Boohs. 



the spectrum : those rays which destroyed phosphorescence 

 were distinctly visible, as were also those which excited it. 

 The tablet was placed in contact with a sensitive plate and de- 

 veloped. The wave-lengths were determined by placing a 

 liquid in front of the slit and noting the place where the 

 known absorption-bands in the infra-red region occurred, 

 which is here shown by these localities remaining of the same 

 luminosity on the tablet surrounding the impressed spectrum. 

 The rays which destroy phosphorescence of this description 

 are shown in IV. It will be noted that in the infra-red 

 region is a portion which does not destroy it. When the wave- 

 lengths of this are compared with the wave-lengths of the exci- 

 ting portion about G and H, it is found that they are octaves 

 one to another. (In the figure the infra-red region is much 

 compressed, owing to the spectrum used being a prismatic 

 spectrum.) 



This fact appears remarkable and worthy of note. My own 

 impression is that another band below this may also be traced; 

 but as it was not shown upon the photographic plate, I have not 

 mapped it. Such a band would probably be another octave 

 below the second band. It should be noted that the infra-red 

 band apparently is of the same luminosity as the general lumi- 

 nosity of the plate, and that these rays only feebly excite the 

 plate. 



I have endeavoured to make out any spectral difference in 

 the light excited about H and about Gr, and have failed to 

 obtain evidence as to any alteration in colour. It seems in- 

 different whether phosphorescence be excited by the indigo or 

 by the violet rays. • 



I am at present engaged upon other phosphorescent material. 



XXV. Notices respecting New Books. 



Lecons sur V Llectricite et le Magnetisme. Par E. Mascabt et J. 

 Joubeet. Tome I. Paris : G. Masson. 1882. 

 ^JTHIS is a work whose value is not to be judged on its absolute 



A merits, though these are in many places of a high order. Like 

 the former treatise by M. Mascart, it is to be looked on as intended 

 to fill an almost absolute gap in modern French scientific literature. 

 The nation that once could boast of Fourier, Lagrange, Laplnee, 

 and Poisson, has never since been without Avorfliy representatives 

 in the front ranks of mathematicians. Galois, Cauchy, Leverrier, 

 and Chasles are names never to be forgotten ; and the veteran 

 Liouville, with De Saint- Venant, Hermite, and others, still uphold 

 in that department the prestige of the Academy of Sciences. But 

 the successors of Ampere and .Sadi Carnot — masters of the still 

 higher art of applying mathematical reasoning to new fields of 



