MEMOIR OF THE LATE PROF. E. HODGKINSON, F.R.S. 161 



ciently examined/' (See Playfair's 'Outlines/ vol.i. p. 153.) 

 Prof. Barlow, in his ' Essay on the Strength and Stress of 

 Timber/ published in 18 17, at p. 32, shows in an ad- 

 mirable manner the inaccurate views of Dr. Uobison re- 

 specting the determination of the neutral line, but fails 

 entirely to remedy the defect. Barlow proposes, what is 

 equally ineffective, to fix the position of the neutral line, 

 by supposing the moments of the extended fibres about 

 the neutral axis to be equal to the moments of the com- 

 pressed fibres about the same line." Sir J. Leslie, in his 

 'Elements of Natural Philosophy/ published in 1823, at 

 p. 234, states that " in the case of a horizontal beam sup- 

 ported at both ends, but depressed by its own weight, the 

 upper surface becomes concave, and the under surface 

 convex. The particles of the upper surface are therefore 

 mutually condensed; in a certain intermediate curve the 

 particles are not affected longitudinally, though bent from 

 their rectilineal position. This curve of neutral action 

 may be assumed in the middle of the beam.'' Dr. O. 

 Gregory, in his ' Mechanics,' published in 1826, at p. 122, 

 vol. i., states, in reference to the subject of the neutral line, 

 " There is, moreover, the consideration that, when a beam 

 deposited horizontally, or nearly so, is ruptured by a ver- 

 tical pressure, a horizontal stratum, from end to end, is 

 compressed, and the other portion extended or stretched, 

 the thin lamina between these two being regarded as a 

 neutral axis ; this again is a curious topic of inquiry." 

 This author gives several theories of the strength of ma- 

 terials from Venturoli, not any one of which contains the 

 correct determination of the neutral line. From these 

 quotations of the best-informed writers, are we not justified 

 in the inference that to the late Prof. Hodgkinson be- 

 longed the merit of first accurately conceiving the true 

 mechanical principle by which the position of the neutral 

 line, in the section of fracture, could be determined ? He 



SER. III. VOL. II. M 



