184 Profs. Richardson and Cooke on the Heat developed 



can be summarized by the following rules, according as the 

 number of readings is odd or even : — 



1. Odd number of readings. To half the first and last 

 add twice all the other odd readings. From this subtract 

 3/2 times the second and last but one, plus twice all the other 

 even readings. 



2. Even number of readings. To half the last plus 3/2 

 times the second add twice all the other even readings. 

 From the sum subtract half the first, plus 3/2 times the last 

 but one, plus twice all the other odd terms. 



In each case the value thus obtained will be n— 2 times 

 the effect of putting on the current, if there are n readings. 



§ 5. Results of the Experiments. 



Experiments were made first with a grid cut out of 

 platinum foil "0031 cm. thick. The mean width of the strip 

 was "041 cm. and its length was about 27 cm. Its resistance 

 was 10'04 ohms at 14 C. and varied from about 13 to 15 

 ohms during the experiments while the measurements were 

 being taken. This increase in the resistance was due to the 

 increase in the temperature of the strip caused by the thermal 

 radiation from the hot osmium filaments. For this reason 

 the effect is measured not at the temperature of the room, 

 but at some higher temperature, which may be calculated 

 from the change in the resistance of the filaments. The 

 resistance of the leads to the grid was '08 ohm, and this has 

 to be subtracted from the above values in calculating the 

 temperature. 



This grid was experimented with under two different sets 

 of conditions. In the first set before each experiment it was 

 placed in a beaker containing nitric acid and made the 

 positive electrode while the acid was electrolysed. In this 

 way nascent electrolytic oxygen was deposited on it for 

 various lengths of time. In the other set of experiments 

 the grid was made the negative electrode in the electrolytic 

 cell, filled with the dilute sulphuric acid, so that nascent 

 electrolytic hydrogen was deposited on it for various lengths 

 of time. It has been shown by H. A. Wilson * that when 

 platinum is made the positive electrode in an electrolytic 

 cell containing nitric acid for a considerable length of time, 

 *nd subsequently heated, it is found to give a relatively small 

 emission of negative electrons, and this corresponds to a large 

 value of iv. Saturating the wire with hydrogen, either 

 electrolytically or otherwise, is found to endow it with the 



* Phil. Trans. A, vol. ccii. p. 243 (1903). 



