188 SCIENCE PROGRESS 



lates the nodes in vibrating rods formed by the rotation of 

 curves y = A x n , o<n<i, about the axis of x, in connection with a 

 theory on the siliceous deposits on certain sponge spicules. 



Ganesh Prasad {Phil. Mag. (6) 34, 138-42, 191 7) considers 

 certain laws of density in a symmetrical sphere, that do not 

 conform to Poisson's equation and to Petrini's generalisation. 



Guillet {Comptes Rendus, 165, 1050-52, 191 7) makes a plea 

 for the measurement of g by the Newtonian method of noting 

 the fall of a body in a short time, as against Galileo's pendulum 

 method. The author urges that the modern refined methods 

 of measuring distances and very short intervals of time make 

 Newton's method more accurate than Galileo's in view of the 

 considerable number of sources of error in a pendulum. 



S. Brodetsky {Quart. Jour, of Math. 48, 58-76, 191 7) calcu- 

 lates the attraction of equiangular spirals of various laws of 

 density, and considers a dynamical consequence. 



Dynamics.— Andrew Gray {Phil. Mag. (6) 35, 181-9, 191 8) 

 gives the history of the hodogaph and discusses several points 

 of interest in the problem of two bodies. 



C. V. Raman and Ashutosh Dey {Phil. Mag. (6) 34, 129-37, 

 191 7) give an experimental and theoretical investigation of 

 the vibrations of a steel wire under a periodic magnetic 

 force. It is shown that the wire can have vibrations with the 

 periodic force applied at a node, the ordinary forced vibrations 

 being unstable. 



E. H. Barton and H. Mary Browning {Phil. Mag. (6) 34, 

 246-70, 191 7) describe experiments conducted on mechanical 

 models illustrative of the types of harmonic oscillations in 

 coupled electric circuits. The method is an extension of the 

 Blackburn pendulum. In one type of experiments two equal 

 pendulums are joined by a stiff connector ; in a second type, 

 one pendulum is suspended from a point on the lath of the other. 

 Unequal pendulums are considered in a second contribution 

 ((6) 35, 62-79, 1918). H. C. Plummer ((6) 34, 510-17, 1917) 

 objects that the analogy is not sufficiently close to be of use 

 to non-mathematical students of electricity, and the authors 

 reply ((6), 35, 203-5, 191 8). Sir G. Greenhill adds a note on 

 Perigal's experiments ((6), 35, i4°> i9 J 8). 



Thybaut {Comptes Rendus, 165, 55-6, 191 7) extends into three 

 dimensions Puiseux' work on tautochronous curves under a 

 central force. 



