528 Dr. L. T. More on Dielectric Strain. 



At present, the relations between the aether and matter are 

 receiving much attention, and this particular one has excited 

 such conflicting opinions that it is worth while to bring as 

 much discussion as possible to bear upon it. I wish, then, 

 to explain my experiments more fully, especially as Dr. 

 JSacerdote has certainly misunderstood some fundamental 

 statements made in my former paper. 



The main point in his criticism of my paper was that the 

 negative results o£ my experiments prove they were carefully 

 performed^ since the apparatus was not sensitive enough to 

 obtain positive results. This was due to the fact that it was 

 designed to measure displacements of the size found by 

 Prof. Quincke and not the much smaller ones found by 

 Prof. Cantone, whose numerical results can be relied on alone. 



To answer this objection, let us assume Prof. Cantone's 

 results to be correct and apply them to my apparatus. 



If I be the length of the condenser, 



£/ be the elongation for a potential V, and 

 d be the thickness between the electrodes, 



then hi d 2 n 1ft „ 



j x^ = 6xl0- 13 . 



Substituting values found on p. 204 of my paper, we obtain 

 a deflexion of 3'5 divisions of the micrometer of the micro- 

 scope. Dr. Sacerdote states, '' A displacement which evidently 

 could not be observed with certainty, since on pp. 202, 203 

 of his paper Prof. More mentions displacements of the zero 

 of the micrometer which exceed 3 divisions/'' 



The displacements referred to occurred while making ob- 

 servations for Young's modulus to test the accuracy of the 

 tilting mirror in recording changes of length. They were 

 not at all due to inaccuracy of the apparatus or to the fact 

 that I could not read less than three divisions, but are simply 

 the residual effects which always occur when measuring 

 elasticity. For example, when 500 grams were placed on 

 the tube the diminution in length was 16*7 divisions; when 

 taken off the increase was 14 divisions, leaving a displacement 

 of 2 '7 divisions, caused not by the fact that I could not detect 

 2*7 divisions, but because the glass did not return in the 

 given time to its original length. Instead of showing a 

 defect these displacements show clearly that much less than 

 three divisions could be read. In fact, I distinctly state that 

 a deflexion of one division could be read accurately, and that 

 the microscope could be set to a quarter of one division. 

 These limits have been obtained by others using a catheto- 

 meter microscope, so I thought it unnecessary to ' state how 



