1 1 MM. Lecher and Pernter on the Absorption 



The method of conducting the experiments was as follows: — 

 After the quantity of water in the heating-apparatus and the 

 pressure of the gas had been adjusted and the water made to 

 boil rapidly, one of us observed the galvanometer, whilst the 

 oilier held himself ready to adjust the tube through which 

 the steam was issuing in the tube I. At a signal from the 

 observer at the galvanometer the steam-tube was put into its 

 place. The position of rest of the galvanometer was observed 

 at the moment of giving the signal ; the current produced 

 drove the needle away; and the first deflectioirand three re- 

 versal-points besides were noted. The whole observation 

 occupied about 1^ minute. We believe that in this way we 

 have completely avoided all errors resulting from air-currents 

 produced. In fact, it could be seen from intentionally pro- 

 tracted observations, of which we made many for the purpose, 

 that when the maximum was reached at the time of the third 

 reversal-point it remained constant at the time of the fourth, 

 but that generally a slight increase could bo observed in the 

 time from the third to the fourth. Not until the sixth, and 

 sometimes not until the eighth reversal, did the air-currents 

 become perceptible. The logarithmic decrement for the 

 vibrations of the pair of needles was determined as often as 

 possible ; and the true deflection calculated from the three 

 reversal-points, after the first deflection had taken place, by 

 means of the formula 



deflection ^ +^> + *(f' + ^> -B, 



where h is the ratio of the amplitudes of two consecutive 

 vibrations, R the original position of rest, and p 2 , p 3 , p± the 

 reversal-points. The first deflection is not employed, since 

 the rapidity with which the steam-tube was placed in I and 

 similar accidents might affect it. 



Calculation showed that it was unnecessary to reduce parts 

 of the scale to corresponding arcs. After each experiment 

 was concluded in the manner described, the tube v was 

 brought again into its original position, and by opening the 

 clamp o for a time the original level of the water was re- 

 stored ; the small space above a was also carefully dried. 



A whole series of experiments was so arranged that the first 

 three experiments were made in vacuo at intervals of 30 

 minutes. Then the galvanometer was put out of the circuit 

 by connecting the conducting-wires Avith each other by a 

 copper bridge so that A could be exhausted. If the galva- 



