262 Prof. E. Wiedemann on the 



2100 «7n r 

 3*14 xP =6 ° C m ' 



i. e. in each minute a column of gas 670 centim. long passes 

 in front of the slit. In 30 minutes 1*025 gr. would be 

 scattered, therefore in 1 minute 0*034 gr. A column of 

 1 centim. height and 2 centim. diameter contains therefore 



W =5x 10 gr '' 



and in 1 cub. centim. 



5 ^~ 5 = 1*59 x 10- 5 gr. fluid dust. 

 3*14 fe 



With the concentration chosen 1 cub. centim. of the flame 

 contains 



4*8 x 10 -7 gr. sodium. 



Let us now calculate the quantity of sodium in a parallelo- 

 piped of unit height and breadth, therefore of the unit of 

 radiating surface and of the thickness of the flame as depth, 

 i.e. 2 cub. centim.; it contains in round numbers 

 9'6 x 10~ 7 gr. sodium. 



This quantity of 9*6 x 10~ 7 gr. sodium therefore radiates 

 the quantity of energy per second 



E'= 0*00203 CQ1 ! tan 'fi l =0*00308 cm. g. sec. calories, 

 contair 36^ ° 



The coefficient of total emission of sodium, i. e. the quantity of 

 energy radiated by 1 gr. sodium in the two yellow lines of the 

 Bunsen flame amounts to 



3210 g. calories per second , 



from which we obtain upon the assumption (no doubt not 

 strictly correct) of equal brightness, 1600 gr. calories per 

 second for each line. 



An atom of sodium weighing 1*7 x 10 -21 gr. emits per 

 second 



5*5 x 10~ 18 gr. calories. 



27. We found before that 1 gr. platinum radiates on the 

 whole 2*2 x 10 4 gr. calories per second,, now we find that with 

 sodium for the two isolated spectrum lines the same value 

 amounts to 3*2 X 10 3 , which is not so much less. It is as if the 

 energy emitted, which with platinum is distributed through- 

 out the entire spectrum, were with sodium concentrated in 

 the two lines. 



In the case of sodium we have besides the energy of the 

 infra-red rays present according to the researches of Ed, 



