[cox A- cali.wndak] experiments ON THE X-RAYS 181 



thiit llie X-rays were tible to penetrate a thickness of a quarter of 

 an inch of condenser with little absorption. We hoped in this manner to 

 be able to obtain readings witli greater rapidity and accuracy, and also to 

 be able to use a balance method for comparing the intensities of the 

 radiation in ditterent directions simultaneously. 



The condensers thus made were inclosed in a screen of aluminium 

 foil connected to earth, in order to protect the galvanometer from the 

 direct etfectof the electrification due to the discharge. Four condensers 

 were made of different sizes and capacities. Some trouble was expe- 

 rienced at fii'st in making the leakage sufficiently small. When this 

 difficulty was overcome, and a small condenser had been made of suitable 

 capacity and sufficiently free from leakage, it was found that the etfect to 

 be observed, although measurable, was very transient. The X-rays 

 apparently did not render the dielectric a conductor so long as they were 

 passing through it, but produced only a temporary effect equivalent to 

 an absorption current. We 'did not, however, determine whether the 

 absorption were actually increased by the incidence of the rays, our main 

 object being to test a method of measurement of the intensity of the rays, 

 which the experiment proved to be impracticable, or at least to have no 

 advantages over the electrometer method. 



Absoiytioti of XSays by Liquids. — We incidentally made a few 

 experiments on the absorption of the X-rays by different liquids and 

 solutions of different thicknesses. The liquids to be compared were 

 inclosed in four vertical lead pipes Avith thin ebonite bottoms, which 

 were filled Avith the liquids to the desired depths, and placed on a photo- 

 graphic jDlate beneath the focus tube. It was not of course possible with 

 a photographic plate to obtain accurate photometric measurements of the 

 coefficients of absorption. The comparative results, however, would be 

 correct, and might be expected to give valiuable information with regard 

 to the degree of penetration and the time of exposure reqitired for taking 

 anatomical cases. The object photographed in each case was a small 

 hole in a lead plate placed over the top of each tube. The shadow of 

 this hole showed as a small and sharp circular spot on the plate. 



We found the opacity of water to be much greater than we had 

 expected. Our exjiectation, however, was pi'obably biassed by the great 

 transparency of water to ordinary light. As a rough estimate, the 

 coefficient of aljsorption of water for X-rays, appeared to be at least a 

 hundred times greater than for light. It appeared to be much more 

 opaque to the X-rays than paper, wood, leather, or other dry fibrous 

 material of an organic nature. 



The absorption was considerably increased b}' the presence of acids 

 or salts, in proportion to the strength of the solution. The opacity did 

 not appear to depend upon the electrical conductivity, but rather on the 

 atomic weight of the metallic constituent of the salt. For instance, a 



