Notices respecting New Books. 365 



time, forms a brittle straw-coloured mass, non-fusible at 

 100° C. The mass was dried at 100° C. till it became con- 

 stant in weight. It was then analyzed: 0*813 grm. contained 

 0*1044 grm. of calcium, or Ca per cent. = 12*84. The formula 

 C 4 H 4 CaN0 2 , 2H 2 requires Ca per cent. = 12*99. 



On raising the temperature this salt shows great stability; 

 and a short heating to 200° C. drives off hardly 4 per cent., 

 which is less than half an atom, of water. 



The salt is very soluble in water, and on mixing the aqueous 

 solution with an equal volume of 84-per-cent. alcohol, gives an 

 abundant powdery precipitate. No doubt this property might 

 be taken advantage of to afford a means of purification. 



LYIII. Notices respecting Neiv Books. 



tSur les Courbes dues a la Combinaison cle deux Mouvements vibratoires 



perpendiculaires. Par M. A. Terqtjem. Lille : imprimerie L. 



Danel; 1879. (8vo, pp. 36.) 

 HPHIS paper is divided into four parts. In the first the Author 

 -**- states, by way of preliminary, the method of obtaining the 

 equations to the Acoustic Curves by the use of Lisajous's Cylinder ; 

 in the second he investigates the properties of the curves as de- 

 scribed on the developed surface of the cylinder ; in the third he 

 discusses the properties of the curves resulting from the projection 

 of these cylindrical curves on a plane containing the axis — 

 these projections being, of course, the acoustic curves themselves ; 

 and in the fourth he obtains a method of making models of the 

 curves as drawn on the cylinder. His method is merely this : — 

 He traces the developed curve on cardboard, and cuts it out, leaving 

 it of a sufficient thickness ; he then bends it into the required form 

 round a wooden cylinder, and gums the edges together ; when the 

 gum is quite dry he removes the cylinder ; and on duly mounting 

 the cardboard, which retains the cylindrical shape, he has the model 

 of the curves. 



The substance of the paper is comprised in sixteen theorems, six 

 relating to the cylindrical curves and ten to their projections. One 

 of the chief of these theorems, relatiug to the projections, is the 

 following : — "There exist in general 2mn— (m + ») intersections, 

 situated on lines parallel to the axes of oc and z ; some of these pa- 

 rallels vary when A varies ; others remain fixed " (p. 20). In this 

 enunciation m is the number of rotations of the cylinder, n the 

 number of oscillations of the molecule, and A-i-m the phase at the 

 beginning of the time. In illustration of this theorem, the author 

 draws the curves corresponding to ten values of A for m=4 and 

 n—3, and for m = 5 and n = 3, i. e. for a fourth and a major sixth. 

 These curves, though more complicated, correspond, of course, to 

 those given for the octave, twelfth, and fifth' in Lord Bayleigh's 

 ' Treatise on Sound ' (vol. i. p. 29), which also would serve to illus- 



Phil, Mag. S. 5. Vol. 7. No. 44. May 1879,. 2 F 



