342 M. F. Kohlrausch on the Absolute Value of the 



place with its attendant increase of volume at high temperatures 

 may be shown as follows : — 



Take a strip of thin sheet palladium, 4 or 5 centims. long 

 and about 5 millims. in breadth, clamp it firmly by the end in 

 a suitable support so that the strip is free to vibrate, and insert 

 it edgeways in the middle of a hydrogen-flame burning from a 

 nozzle about a millimetre in diameter. If the palladium is now 

 depressed into the inner dark cone, it immediately begins to vi- 

 brate, producing a low musical note. 



If the flame be extinguished by stopping the current of hy- 

 drogen for an instant, or allowing the gas to flow, the vibration 

 commences again, and may be kept up without any actual flame. 



The motion in this position in the flame is due to the absorp- 

 tion of hydrogen on the cool side next the inner cone, with its 

 attendant increase of length, producing a bending of the sheet 

 into the hot portion of the flame, where the hydrogen is instantly 

 expelled from the palladium, which is forced to return to its 

 original position from its natural elasticity. 



The experiments detailed in this paper have been made with 

 palladium very handsomely placed at my disposal by Messrs. 

 Johnson, Matthey, and Co. of Hatton Garden, London; and I 

 gladly avail myself of this opportunity of thanking them for the 

 means of conducting this research. 



XLII. Determination of the Absolute Value of the Siemens Mer- 

 cury Unit of Electrical Resistance. By F. Kohlrausch. 

 [With a Plate.] 

 [Continued from p. 309.] 



V. Data of Observation. 



EOK determining the three fundamental magnitudes, length, 

 mass, and time, there were used the original platinum 

 metre belonging to the Cabinet for Metals and Machinery in 

 Gottingen (and kindly lent for the purpose by Professor Ulrich), 

 a Fortin's set of platinum weights belonging to the Physical 

 Institute, and the normal clock of the Astronomical Observatory 

 (by which that in the Physical Observatory was regulated). Oert- 

 ling^s comparator, which formed the basis of all the measure- 

 ments, was compared with the platinum metre. It was found 

 that the parts of this bar at —8° were equal to the divisions of 

 the platinum metre at 0°. 



For measuring the larger distances, a wooden rod 5 metres in 

 length, divided into centimetres and provided with a slider di- 

 vided into millimetres, was used. The divisions were afterwards 

 compared with the Oertling. This was also the case with the 

 divisions of the paper scale which was used for observation. 



