324 Dr. A. M. Mayer on a Method of detecting the Phases 



as one series of serrations in the rotating mirror. Now, on gra- 

 dually moving the resonator away from the pipe, I saw another 

 series of serrations (produced by the resonator-flame) slowly 

 evolve themselves from the first series and gradually slide over 

 the latter, until, having removed the resonator from its first posi- 

 tion by about 66 centimetres, or half a wave-length (German), 

 I had the pleasure of seeing the series of moving serrations stand 

 exactly between the first (or immoveable) series. On moving the 

 resonator yet further from the sounding-pipe, I saw the ser- 

 rations of the resonator-flame continue their onward progress 

 until the two series again coincided ; and on measuring the dis- 

 tance of the resonator from its first position near the pipe, I 

 found it to be equal to the whole wave-length of UTg. When 

 I had removed the resonator one and a half wave-length, I again 

 saw the serrations of the resonator- flame bisecting the spaces 

 between the serrations given by the organ-pipe flame; and when 

 the resonator had progressed from the pipe to a distance equal 

 to two whole wave-lengths, I saw that the serrations of its flame 

 had progressed to another coincidence with those of the organ 

 pipe, and so on, until I had determined on the line of the re- 

 sonator^s motion all the phases of vibration corresponding to 

 three whole wave-lengths. I now moved the resonator until 

 I had again caused the serrations of its flame neatly to bisect 

 the spaces between the serrations of the organ-pipe flame ; and 

 moving round the organ-pipe, with the resonator held at such 

 distances from it that the bisections were steadily kept_, I de- 

 scribed in space the wave-surface of the sounding-pipe. This 

 wave-surface I found to be approximately an ellipsoid, with its 

 foci at the top and bottom of the pipe. Nothing could be more 

 satisfactory ; and it was charming to behold how neatly the wave- 

 surface could be determined ; for a small change in the distance 

 of the resonator from the pipe produced a sensible shifting of 

 the serrations. 



I now substituted for the resonator an organ-pipe, in every 

 respect similar to the one on the bellows ; and with it I repeated 

 the wave-length measures previously made with the resonator; 

 indeed the column of air in the pipe in my hand responded so 

 perfectly to the sounding-pipe that I thought it gave more 

 marked results than those produced with the resonator. 



The Manometric Flame-micrometer, 

 In the experiments described above we examined the appear- 

 ances in the mirror with the unaided eye, and with it estimated 

 when bisections and coincidences occurred ; but to obtain results 

 of precision, a method was devised which determines neatly these 

 critical points. For that purpose I have invented the following 



