Intelligence and Miscellaneous Articles. 465 



An Elementary Treatise on the Differential Calculus, containing the 



theory of Plane Curves, with numerous examples. By Benjamin 



Williamson, M.A., F.B.S. London : Longmans. 1884, (Pp. 



xvi+454.) 



Mr. Williamson's works certainly meet the wants of a large 



class of students. His treatise on the Integral Calculus has reached 



a f ourth edition, and the present work, an elder child, is now in its 



fifth edition. As time rolls on, so come the announcements of a 



new edition of one or the other work ; and, as with the human 



offspring so with these, increase of age brings increase in size and 



knowledge. Mr. Williamson does not rest satisfied with so much 



good work achieved, but his motto is " onward,'' and so of the 



present treatise we can say " vires acquirit eundo." 



Our author is ever careful to inform his readers that his book is 

 principally intended for the use of beginners, but we fancy that in 

 time he will leave little untouched that may concern the most 

 advanced students. It would be now out of place to discuss such 

 a work as this, upon which the world of mathematical students has 

 stamped so clearly its " Imprimatur." It is for us only to wish 

 "more power" to the able author, and trust that he will meet 

 with like success in those new pastures in which, we learn, he is 

 now expatiating — we allude to his forthcoming treatise on Dynamics. 

 We may note that the chapter on Roulettes and on the Enve- 

 lope of any Curve carried by a rolling Curve is put more shipshape 

 than in some of the earlier editions ; that there is a full account of 

 the Cartesian oval, a direction in which our author has done much 

 good work; and, to crown all, the "latest novelty" is a short 

 account of the Determinant functions yclept Jacobians — of which 

 we expect to hear more in the ' Dynamics.' We wish Mr. William- 

 son's treatise a " bon voyage." 



LIII. Intelligence and Miscellaneous Articles. 



DETERMINATION OF THE WAVE-LENGTHS OF THE PRINCIPAL 

 LINES AND BANDS IN THE INFRA-RED PORTION OF THE SOLAR 

 SPECTRUM. NOTE BY M. HENRI BECQUEREL. 



TN a recent communication to the Academie des Sciences* on the 

 -*- lines in the infra-red part of the spectrum formed by incan- 

 descent metallic vapours, I had occasion to point out some correc- 

 tions which I had been led to make in the numbers adopted in a 

 previous researchf for the wave-lengths of several lines and bands 

 in the solar spectrum. I now give a resume of my new determina- 

 tions of the wave-lengths of the principal lines and bands in the 

 infra-red portion of the solar spectrum. 



The infra-red portion of the solar spectrum, from the group A 



* Comptes Renclus, August 25, 1884; Phil. Mag. October, p. 386. 

 + Annates de Chimie et de Physique, o e serie, t. xxx. p. 5. 



