90 Mr. S. U. Pickering on Mr. Lupton's Method of 



pivoted in the middle, and kept vertical by a weight attached 

 to the other end. By means of two screw-stops the excur- 

 sion to either side of the vertical position is limited to any 

 desired amount. The method of procedure in identifying a 

 node is, then, to find a position for the resonator such that on 

 moving it an equal amount to either side, sparking just takes 

 place. This can of course be done with facility in a darkened 

 room. 



When possible, it is still more convenient to move the re- 

 flector backwards and forwards a known amount, instead of 

 moving the resonator, and the node is found similarly to 

 before as the position where sparking just occurs in the ex- 

 treme position of the reflector ; this admits of being done 

 when the reflector is small. The reflector was suspended by 

 vertical cords about 3 m. long, and could be thus moved 

 backwards and forwards practically parallel to itself with 

 the greatest ease even in the dark, the amount of the move- 

 ment being limited by stops. The advantage of this arrange- 

 ment is that the adjustment of the resonator is unaffected, for 

 when it is the resonator that is moved the disturbance is very 

 liable to alter the spark-gap. 



I have much pleasure here in thanking Prof. Fitzgerald 

 for his advice and material encouragement on many occasions 

 throughout the investigation. 



Note. — Since sending off to the printers' I have learnt that 

 MM. Sarasin and De la Kive (Phil. Mag. June 1891) have, 

 unlike Hertz, observed do inward displacement of the node 

 towards the reflector. Their experiments are quite in agree- 

 ment with the explanation given above, for their reflector 

 was about a wave-length in the direction of the magnetic 

 component. 



XV. Mr. Sydney Lupton's Method of Reducing the Results 

 of Experiments. By Spencer Umfreville Pickering, 

 M.A., F.R.S.* 



THE conclusions which I drew from an examination of 

 various properties of sulphuric-acid solutions (Chem. 

 Soc. Trans. 1890, pp. 64 and 331 ; Phil. Mag. xxix. p. 427) 

 have recently been made the subject of an adverse criticism 

 by Mr. Sydney Lupton in the pages of this Magazine 

 (vol. xxxi. p. 418). 



* Communicated by the Author,, 



