284 SCIENCE PROGRESS. 



whole situated more to the refrangible part of the spectrum, 

 one may, independently of the diffusion experiment, con- 

 clude that the element corresponding to the second set is the 

 heavier of the two ". 



As they themselves pointed out, however, the result was 

 not final, because the pressures were not the same. I have 

 recently made some experiments in which the pressures 

 remain the same. 



An U tube was taken, and at the bend was fixed a 

 plaster of Paris plug about 1*5 cm. thick; in one of the 

 limbs two platinum wires were inserted. The plug was 

 saturated with hydrogen to free it from air ; the tube was 

 then plunged into a mercury trough, and fixed upright with 

 the limbs full of mercury. Into the leg (A) with the plati- 

 num wires a small quantity of hydrogen was passed, and as 

 soon after as possible another small quantity of a mixture 

 of helium and hydrogen from samarskite was put up the 

 other limb (B) of the U tube. 



Immediately after the helium was passed into the limb 

 (B) spectroscopic observations were made of the gas in the 

 limb (A) ; D 3 was already visible, and there was no trace of 

 50157. This result seems to clearly indicate that if a true 

 diffusion of one constituent takes place, the component which 

 gives D 3 is lighter than the one which gives the lines at 

 wave-length 50157. 



Although this result is opposed to the statement made 

 by Runge and Paschen, it is entirely in harmony with the 

 solar and stellar results. 



In support of this I may instance that of the cleveite 

 lines associated with hydrogen in the chromosphere and the 

 stars of Group III. y ; those allied to D 3 are much stronger 

 than those belonging to the series of which 50157 forms 

 part. 



MINERALS EXAMINED. 



So far I have worked upon some seventy minerals, and 

 I have found the orange line in sixteen. 



The following are the minerals, etc., which have been 



