354 SCIENCE PROGRESS 



Questions in the geometry of the triangle and of the circle 

 are treated respectively by N. Altshiller (Atner. Math. Monthly, 

 25, 241-6) and H. N. Wright (ibid. 250-2). 



G. H. Light {Bull. Amer. Math. Soc. 191 8, 24, 480-1) gives 

 the intrinsic equation for Euler's resistance-integral in his 

 Scientia Navalis. 



A. Emch (ibid. 327-30) gives some theorems on the invariant 

 net of cubics in the Steinerian transformation. 



E. F. Simonds (Trans. Amer. Math. Soc. 191 8, 19, 223-50) 

 deals with the question of absolute invariants of differential 

 configurations in the plane. 



L. P. Eisenhart (ibid. 167-85) applies the results of his paper 

 mentioned in Science Progress (191 7, 12, 13) to a particular 

 class of conjugate systems, namely those which are applicable 

 to one or more other systems. Eisenhart (Amer. Journ. Math. 

 191 8, 40, 1 27-44) continues his investigations on transformations 

 of planar nets, contained in the paper of 191 7 just referred to. 



T. Dantzig (ibid. 187-212) makes some contributions to the 

 geometry of plane transformations. 



Pauline Sperry (ibid. 213-24), starting from Wilczynski's 

 five memoirs (1907-9) on projective differential geometry of 

 curved surfaces, discusses the properties of a certain projectively 

 defined two-parameter family of curves on a general surface. 



A. L. Miller (ibid. 174-86) applies some of the results of 

 investigations of the projective differential properties of geo- 

 metric configurations in n dimensions by synthetic methods, of 

 which the foundation was laid by Segre (1910), to the study 

 of families of pencils of lines in ordinary space. 



P. R. Rider (Bull. Amer. Math. Soc. 191 8, 24, 430-1) gener- 

 alises a well-known theorem of differential geometry concerning 

 the variation of a function. 



F. H. Safford (ibid. 384-90) continues work of Wangerin 

 (1878) and Haentzschel (1893) on surfaces of revolution in the 

 theory of Lamp's products. 



G. M. Green (ibid. 221-5) gives a completion and generalisa- 

 tion of his new characterisation of conjugate nets on a curved 

 surface with equal Laplace-Darboux invariants (Amer. Journ. 

 Math. 1 91 6, 38, 287-324). 



On algebraic curves and surfaces, see also F. Gomes Teixeira 

 (Nouv. ann. 191 7, [4], 17, 281-9), A. Crespi (Giorn. di Mat. 1917, 

 55, 48-82), and G. Grimaldi (ibid. 191 6, 54, 341-64). On 



