400 Mr. R. C. Nichols on the Resistances 



Before proceeding to inquire further into the real cause of 

 the actual amount of resistance found to exist in bars sub- 

 jected to transverse strain, it will be desirable to examine 

 somewhat closely some of the experiments detailed by Mr. 

 Barlow, and the conclusions drawn from them by him for the 

 purpose of establishing his theory. 



His first set of experiments were made " in order to estab- 

 lish clearly the position of the neutral axis;" and he states 

 that they lt point it out as the centre of the beam in a manner 

 so decided as to remove all further doubt on the subject, not 

 only in the smaller strains but in the larger ones, which were 

 carried to about three fourths of the breaking weight"*. 



Mr. Barlow's experiments were conducted with extreme 

 care, and Ins measurements made with all the accuracy which 

 circumstances would permit. He observes that " considering 

 the very minute quantities which had to be measured, and the 

 numerous causes of disturbance to which observations of such 

 delicacy were liable, such as changes of temperature, or want 

 of perfect uniformity in the dimensions or texture of the 

 beams, the results exhibit much more regularity than could 

 have been expected." 



These experiments were made upon cast-iron beams or 

 bars " 7 feet long f, 6 inches deep, and 2 inches in thickness, 

 on each of which were cast small vertical ribs at intervals of 

 1 2 inches : these ribs were J inch wide and projected | inch 

 from the beam. In each rib nine small holes were drilled to 

 the depth of the surface of the beam for the purpose of insert- 

 ing the pins attached to a delicate measuring instrument, the 

 intention being to ascertain the position of the neutral axis 

 by measuring the distance of the holes in the vertical ribs 

 when the beam was placed under different strains" J. 



Mr. Barlow does not state the distance between the holes, 

 nor whether the accuracy of their relative distances was 

 tested in any way. The only indication given on this point 

 is the statement that the elongation at the lowest point mea- 

 sured was j^ths of that of the outer fibres. This implies that 

 the distance of the last hole from the lower (or upper) side 

 was £ inch, giving for the distance between the holes 5 J inches 



* Phil. Trans, 1855, p. 228. 



f In the plate the beams are figured as 7 feet 4 inches long, and in 

 another place in his paper Mr. Bailow refers to them as of this lerjgth, 

 but in the absence of definite and consistent statement it may be con- 

 cluded that the distance between the points of support was 7 feet, while 

 7 feet 4 inches was the total length. 



X Phil. Trans. 1855, p. 225. 



