188 ESSAYS BIOGRAPHICAL AND CHEMICAL 



weight of any element would occupy in the state of gas), 

 to calculate how long it would take for the radium to be 

 converted into emanation, supposing that to be its only 

 product. This gives for half of the radium to be decom- 

 posed about 1150 years. But there is a good deal of 

 conjecture about the calculation; for many unproved 

 assumptions have to be made. 



A further experiment, conducted in a somewhat similar 

 manner, but with the utmost precaution to exclude every 

 trace of foreign gas, made it possible to measure the 

 position of the lines of the spectrum of the emanation. 

 In general it may be said that the spectrum has a similar 

 character to those of argon and helium ; it consists of a 

 number of bright lines, chiefly green, appearing distinctly 

 on a black background. It confirms the supposition, 

 made after examination of the chemical properties of the 

 emanation, that it is a gas belonging to the argon group, 

 with a very heavy atomic weight. Some of the lines of 

 the spectrum appear to be identical with lines observed in 

 the spectra of the stars ; and it may perhaps be inferred 

 that such heavenly bodies are rich in radium. 



In the diagram on page 184, the bulb containing radium 

 bromide there shown was surrounded by a small glass 

 beaker, as a precautionary measure. As a matter of 

 fact, there were three such bulbs and three such beakers, 

 on the principle of not putting all one's eggs in 

 one basket. These beakers had never been in contact 

 with the radium bromide, nor with the emanation ; but 

 they had been bombarded for months by /3-rays, or 

 electrons, which are so minute, and move so rapidly, that 

 they penetrate thin glass with ease. It was found that 

 these beakers were radioactive ; and it is very remarkable 

 that after washing with water, the beakers lost their radio- 

 activity, which was transferred to the water. Evidently, 

 then, some radioactive matter had been produced by the 



